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  • 1. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J. .
    Bertsche, W.
    Butler, E.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Ishida, A.
    Ohnson, M. A. J.
    Ones, S. A. J.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Madsen, N.
    Mathers, M.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Michan, J. M.
    Momose, T.
    Munich, J. J. .
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    Stracka, S.
    Stutter, G.
    So, C.
    Tharp, T. D.
    Thompson, J. E.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Observation of the 1S-2S transition in trapped antihydrogen2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 541, no 7638, p. 506-510Article in journal (Refereed)
    Abstract [en]

    The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S-2S transition by Hansch1 to a precision of a few parts in 10(15). Recent technological advances have allowed us to focus on antihydrogen-the antimatter equivalent of hydrogen(2-4). The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today's Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S-2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 x 10(-10).

  • 2. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Ishida, A.
    Johnson, M. A.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Madsen, N.
    Mathers, M.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Michan, J. M.
    Momose, T.
    Munich, J. J.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    Stracka, S.
    Stutter, G.
    So, C.
    Tharp, T. D.
    Thompson, J. E.
    Thompson, R. I.
    Van der Werf, D. P.
    Wurtele, J. S.
    Observation of the hyperfine spectrum of antihydrogen2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 548, no 7665, p. 66-+Article in journal (Refereed)
    Abstract [en]

    The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers(1-3) and the measurement(4) of the zero-field ground-state splitting at the level of seven parts in 10(13) are important achievements of mid-twentieth-century physics. The work that led to these achievements also provided the first evidence for the anomalous magnetic moment of the electron(5-8), inspired Schwinger's relativistic theory of quantum electrodynamics(9,10) and gave rise to the hydrogen maser(11), which is a critical component of modern navigation, geo-positioning and very-long-baseline interferometry systems. Research at the Antiproton Decelerator at CERN by the ALPHA collaboration extends these enquiries into the antimatter sector. Recently, tools have been developed that enable studies of the hyperfine structure of antihydrogen(12)-the antimatter counterpart of hydrogen. The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms(13,14) provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter(12,15). Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies. The data reveal clear and distinct signatures of two allowed transitions, from which we obtain a direct, magnetic-field-independent measurement of the hyperfine splitting. From a set of trials involving 194 detected atoms, we determine a splitting of 1,420.4 +/- 0.5 megahertz, consistent with expectations for atomic hydrogen at the level of four parts in 10(4). This observation of the detailed behaviour of a quantum transition in an atom of antihydrogen exemplifies tests of fundamental symmetries such as charge-parity-time in antimatter, and the techniques developed here will enable more-precise such tests.

  • 3. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Ishida, A.
    Johnson, M. A.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Madsen, N.
    Mathers, M.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Michan, J. M.
    Momose, T.
    Munich, J. J.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. Ø.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    Stracka, S.
    Stutter, G.
    So, C.
    Tharp, T. D.
    Thompson, J. E.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Antihydrogen accumulation for fundamental symmetry tests2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 681Article in journal (Refereed)
    Abstract [en]

    Antihydrogen, a positron bound to an antiproton, is the simplest anti-atom. Its structure and properties are expected to mirror those of the hydrogen atom. Prospects for precision comparisons of the two, as tests of fundamental symmetries, are driving a vibrant programme of research. In this regard, a limiting factor in most experiments is the availability of large numbers of cold ground state antihydrogen atoms. Here, we describe how an improved synthesis process results in a maximum rate of 10.5 +/- 0.6 atoms trapped and detected per cycle, corresponding to more than an order of magnitude improvement over previous work. Additionally, we demonstrate how detailed control of electron, positron and antiproton plasmas enables repeated formation and trapping of antihydrogen atoms, with the simultaneous retention of atoms produced in previous cycles. We report a record of 54 detected annihilation events from a single release of the trapped anti-atoms accumulated from five consecutive cycles.

  • 4. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J.
    Bertsche, W.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Hunter, E. D.
    Isaac, C. A.
    Johnson, M. A.
    Jones, J. M.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Khramov, A.
    Knapp, P.
    Kurchaninov, L.
    Madsen, N.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Michan, J. M.
    Momose, T.
    Munich, J. J.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    Starko, D. M.
    Stutter, G.
    So, C.
    Tharp, T. D.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Observation of the 1S-2P Lyman-alpha transition in antihydrogen2018In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 561, no 7722, p. 211-217Article in journal (Refereed)
    Abstract [en]

    In 1906, Theodore Lyman discovered his eponymous series of transitions in the extreme-ultraviolet region of the atomic hydrogen spectrum(1,2). The patterns in the hydrogen spectrum helped to establish the emerging theory of quantum mechanics, which we now know governs the world at the atomic scale. Since then, studies involving the Lyman-alpha line-the 1S-2P transition at a wavelength of 121.6 nanometres-have played an important part in physics and astronomy, as one of the most fundamental atomic transitions in the Universe. For example, this transition has long been used by astronomers studying the intergalactic medium and testing cosmological models via the so-called 'Lyman-alpha forest('3) of absorption lines at different redshifts. Here we report the observation of the Lyman-alpha transition in the antihydrogen atom, the antimatter counterpart of hydrogen. Using narrow-line-width, nanosecond-pulsed laser radiation, the 1S-2P transition was excited in magnetically trapped antihydrogen. The transition frequency at a field of 1.033 tesla was determined to be 2,466,051.7 +/- 0.12 gigahertz (1 sigma uncertainty) and agrees with the prediction for hydrogen to a precision of 5 x 10(-8). Comparisons of the properties of antihydrogen with those of its well-studied matter equivalent allow precision tests of fundamental symmetries between matter ;and antimatter. Alongside the ground-state hyperfine(4,5) and 1S-2S transitions(6,7) recently observed in antihydrogen, the Lyman-alpha transition will permit laser cooling of antihydrogen(8,9), thus providing a cold and dense sample of anti-atoms for precision spectroscopy and gravity measurements(10). In addition to the observation of this fundamental transition, this work represents both a decisive technological step towards laser cooling of antihydrogen, and the extension of antimatter spectroscopy to quantum states possessing orbital angular momentum.

  • 5. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J.
    Bertsche, W.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Johnson, M. A.
    Jones, J. M.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Khramov, A.
    Knapp, P.
    Kurchaninov, L.
    Madsen, N.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Momose, T.
    Munich, J. J.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    Stutter, G.
    So, C.
    Tharp, T. D.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Characterization of the 1S-2S transition in antihydrogen2018In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 557, no 7703, p. 71-+Article in journal (Refereed)
    Abstract [en]

    In 1928, Dirac published an equation(1) that combined quantum mechanics and special relativity. Negative-energy solutions to this equation, rather than being unphysical as initially thought, represented a class of hitherto unobserved and unimagined particles-antimatter. The existence of particles of antimatter was confirmed with the discovery of the positron(2) (or anti-electron) by Anderson in 1932, but it is still unknown why matter, rather than antimatter, survived after the Big Bang. As a result, experimental studies of antimatter(3-7), including tests of fundamental symmetries such as charge-parity and charge-parity-time, and searches for evidence of primordial antimatter, such as antihelium nuclei, have high priority in contemporary physics research. The fundamental role of the hydrogen atom in the evolution of the Universe and in the historical development of our understanding of quantum physics makes its antimatter counterpart-the antihydrogen atom-of particular interest. Current standard-model physics requires that hydrogen and antihydrogen have the same energy levels and spectral lines. The laser-driven 1S-2S transition was recently observed(8) in antihydrogen. Here we characterize one of the hyperfine components of this transition using magnetically trapped atoms of antihydrogen and compare it to model calculations for hydrogen in our apparatus. We find that the shape of the spectral line agrees very well with that expected for hydrogen and that the resonance frequency agrees with that in hydrogen to about 5 kilohertz out of 2.5 x 10(15) hertz. This is consistent with charge-parity-time invariance at a relative precision of 2 x 10(-12)-two orders of magnitude more precise than the previous determination(8)-corresponding to an absolute energy sensitivity of 2 x 10(-20) GeV.

  • 6. Ahmadi, M.
    et al.
    Alves, B. X. R.
    Baker, C. J.
    Bertsche, W.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Cohen, S.
    Collister, R.
    Eriksson, S.
    Evans, A.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Johnson, M. A.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Madsen, N.
    Mathers, M.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Momose, T.
    Munich, J. J.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Stutter, G.
    Tharp, T. D.
    Thompson, J. E.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Enhanced Control and Reproducibility of Non-Neutral Plasmas2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 2, article id 025001Article in journal (Refereed)
    Abstract [en]

    The simultaneous control of the density and particle number of non-neutral plasmas confined in Penning-Malmberg traps is demonstrated. Control is achieved by setting the plasma's density by applying a rotating electric field while simultaneously fixing its axial potential via evaporative cooling. This novel method is particularly useful for stabilizing positron plasmas, as the procedures used to collect positrons from radioactive sources typically yield plasmas with variable densities and particle numbers; it also simplifies optimization studies that require plasma parameter scans. The reproducibility achieved by applying this technique to the positron and electron plasmas used by the ALPHA antihydrogen experiment at CERN, combined with other developments, contributed to a 10-fold increase in the antiatom trapping rate.

  • 7. Ahmadi, M.
    et al.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Carruth, C.
    Cesar, C. L.
    Charlton, M.
    Charman, A. E.
    Eriksson, S.
    Evans, L. T.
    Evetts, N.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Ishida, A.
    Jones, S. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Madsen, N.
    Maxwell, D.
    McKenna, J. T. K.
    Menary, S.
    Michan, J. M.
    Momose, T.
    Munich, J. J.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Sameed, M.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Tharp, T. D.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Zhmoginov, A. I.
    An improved limit on the charge of antihydrogen from stochastic acceleration2016In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 529, no 7586, p. 373-+Article in journal (Refereed)
    Abstract [en]

    Antimatter continues to intrigue physicists because of its apparent absence in the observable Universe. Current theory requires that matter and antimatter appeared in equal quantities after the Big Bang, but the Standard Model of particle physics offers no quantitative explanation for the apparent disappearance of half the Universe. It has recently become possible to study trapped atoms(1-4) of antihydrogen to search for possible, as yet unobserved, differences in the physical behaviour of matter and antimatter. Here we consider the charge neutrality of the antihydrogen atom. By applying stochastic acceleration to trapped antihydrogen atoms, we determine an experimental bound on the antihydrogen charge, Qe, of vertical bar Q vertical bar < 0.71 parts per billion (one standard deviation), in which e is the elementary charge. This bound is a factor of 20 less than that determined from the best previous measurement(5) of the antihydrogen charge. The electrical charge of atoms and molecules of normal matter is known(6) to be no greater than about 10(-21)e for a diverse range of species including H-2, He and SF6. Charge-parity-time symmetry and quantum anomaly cancellation(7) demand that the charge of antihydrogen be similarly small. Thus, our measurement constitutes an improved limit and a test of fundamental aspects of the Standard Model. If we assume charge superposition and use the best measured value of the antiproton charge(8), then we can place a new limit on the positron charge anomaly (the relative difference between the positron and elementary charge) of about one part per billion (one standard deviation), a 25-fold reduction compared to the current best measurement(8),(9).

  • 8. Amole, C.
    et al.
    Andresen, G. B.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Capra, A.
    Carpenter, P. T.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Escallier, J.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A. J.
    Hurt, J. L.
    Hydomako, R.
    Isaac, C. A.
    Jenkins, M. J.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jörgensen, L. V.
    Kerrigan, S. J.
    Kurchaninov, L.
    Madsen, N.
    Morone, A.
    McKenna, J. T. K.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Parker, B.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Seddon, D.
    El Nasr, S. Seif
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    Thornhill, J.
    Wells, D.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    The ALPHA antihydrogen trapping apparatus2014In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 735, p. 319-340Article in journal (Refereed)
    Abstract [en]

    The ALPHA collaboration, based at CERN, has recently succeeded in confining cold antihydrogen atoms in a magnetic minimum neutral atom trap and has performed the first study of a resonant transition of the anti-atoms. The ALPHA apparatus will be described herein, with emphasis on the structural aspects, diagnostic methods and techniques that have enabled antihydrogen trapping and experimentation to be achieved.

  • 9. Amole, C.
    et al.
    Andresen, G. B.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Burrows, C.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sacramento, R. L.
    Stracka, S.
    Sampson, J. A.
    Sarid, E.
    Seddon, D.
    Silveira, D. M.
    So, C.
    Thompson, R. I.
    Tharp, T.
    Thornhill, J.
    Tooley, M. P.
    van der Werf, D. P.
    Wells, D.
    Silicon vertex detector upgrade in the ALPHA experiment2013In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 732, p. 134-136Article in journal (Refereed)
    Abstract [en]

    The Silicon Vertex Detector (SVD) is the main diagnostic tool in the ALPHA-experiment. It provides precise spatial and timing information of antiproton (antihydrogen) annihilation events (vertices), and most importantly, the SVD is capable of directly identifying and analysing single annihilation events, thereby forming the basis of ALPHA's analysis. This paper describes the ALPHA SVD and its upgrade, installed in the ALPHA's new neutral atom trap.

  • 10. Amole, C.
    et al.
    Andresen, G. B.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Kurchaninov, L.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap2012In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, p. 015010-Article in journal (Refereed)
    Abstract [en]

    Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilate. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.

  • 11. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Charlton, M.
    Deller, A.
    Donnan, P. H.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Shields, C. R.
    Silveira, D. M.
    Stracka, S.
    So, C.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Resonant quantum transitions in trapped antihydrogen atoms2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 483, no 7390, p. 439-U86Article in journal (Refereed)
    Abstract [en]

    The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured(1) and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and-by comparison with measurements on its antimatter counterpart, antihydrogen-the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state(2,3) of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped(4-6) in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

  • 12. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    Stracka, S.
    So, C.
    Thompson, R. I.
    Turner, M.
    van der Werf, D. P.
    Wurtele, J. S.
    Zhmoginov, A.
    Autoresonant-spectrometric determination of the residual gas composition in the ALPHA experiment apparatus2013In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 6, p. 065110-Article in journal (Refereed)
    Abstract [en]

    Knowledge of the residual gas composition in the ALPHA experiment apparatus is important in our studies of antihydrogen and nonneutral plasmas. A technique based on autoresonant ion extraction from an electrostatic potential well has been developed that enables the study of the vacuum in our trap. Computer simulations allow an interpretation of our measurements and provide the residual gas composition under operating conditions typical of those used in experiments to produce, trap, and study antihydrogen. The methods developed may also be applicable in a range of atomic and molecular trap experiments where Penning-Malmberg traps are used and where access is limited.

  • 13. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Shields, C. R.
    Silveira, D. M.
    So, C.
    Stracka, S.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Zhmoginov, A.
    Friedland, L.
    Experimental and computational study of the injection of antiprotons into a positron plasma for antihydrogen production2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 4, p. 043510-Article in journal (Refereed)
    Abstract [en]

    One of the goals of synthesizing and trapping antihydrogen is to study the validity of charge-parity-time symmetry through precision spectroscopy on the anti-atoms, but the trapping yield achieved in recent experiments must be significantly improved before this can be realized. Antihydrogen atoms are commonly produced by mixing antiprotons and positrons stored in a nested Penning-Malmberg trap, which was achieved in ALPHA by an autoresonant excitation of the antiprotons, injecting them into the positron plasma. In this work, a hybrid numerical model is developed to simulate antiproton and positron dynamics during the mixing process. The simulation is benchmarked against other numerical and analytic models, as well as experimental measurements. The autoresonant injection scheme and an alternative scheme are compared numerically over a range of plasma parameters which can be reached in current and upcoming antihydrogen experiments, and the latter scheme is seen to offer significant improvement in trapping yield as the number of available antiprotons increases.

  • 14. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Charlton, M.
    Deller, A.
    Evetts, N.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, Silvia C.
    Stockholm University, Faculty of Science, Department of Physics.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Stracka, S.
    Tharp, T.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    In situ electromagnetic field diagnostics with an electron plasma in a Penning-Malmberg trap2014In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, p. 013037-Article in journal (Refereed)
    Abstract [en]

    We demonstrate a novel detection method for the cyclotron resonance frequency of an electron plasma in a Penning-Malmberg trap. With this technique, the electron plasma is used as an in situ diagnostic tool for the measurement of the static magnetic field and the microwave electric field in the trap. The cyclotron motion of the electron plasma is excited by microwave radiation and the temperature change of the plasma is measured non-destructively by monitoring the plasma's quadrupole mode frequency. The spatially resolved microwave electric field strength can be inferred from the plasma temperature change and the magnetic field is found through the cyclotron resonance frequency. These measurements were used extensively in the recently reported demonstration of resonant quantum interactions with antihydrogen.

  • 15. Amole, C.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Butler, E.
    Capra, A.
    Cesar, C. L.
    Charlton, M.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Isaac, C. A.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Little, A.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Napoli, S. C.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Tharp, T. D.
    Thompson, R. I.
    van der Werf, D. P.
    Vendeiro, Z.
    Wurtele, J. S.
    Zhmoginov, A. I.
    Charman, A. E.
    An experimental limit on the charge of antihydrogen2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, p. 3955-Article in journal (Refereed)
    Abstract [en]

    The properties of antihydrogen are expected to be identical to those of hydrogen, and any differences would constitute a profound challenge to the fundamental theories of physics. The most commonly discussed antiatom- based tests of these theories are searches for antihydrogen- hydrogen spectral differences (tests of CPT (charge- parity- time) invariance) or gravitational differences (tests of the weak equivalence principle). Here we, the ALPHA Collaboration, report a different and somewhat unusual test of CPT and of quantum anomaly cancellation. A retrospective analysis of the influence of electric fields on antihydrogen atoms released from the ALPHA trap finds a mean axial deflection of 4.1 +/- 3.4mm for an average axial electric field of 0.51Vmm1. Combined with extensive numerical modelling, this measurement leads to a bound on the charge Qe of antihydrogen of Q (+/- 1.3 +/- 1.1 +/- 0.4)10 8. Here, e is the unit charge, and the errors are from statistics and systematic effects.

  • 16. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Bray, C. C.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jörgensen, L. V.
    Kurchaninov, L.
    Lambo, R.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Seif El Nasr, S.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wilding, D.
    Wurtele, J. S.
    Yamazaki, Y.
    Search for trapped antihydrogen2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 695, no 1-4, p. 95-104Article in journal (Refereed)
    Abstract [en]

    We present the results of an experiment to search for trapped antihydrogen atoms with the ALPHA antihydrogen trap at the CERN Antiproton Decelerator. Sensitive diagnostics of the temperatures, sizes, and densities of the trapped antiproton and positron plasmas have been developed, which in turn permitted development of techniques to precisely and reproducibly control the initial experimental parameters. The use of a position-sensitive annihilation vertex detector, together with the capability of controllably quenching the superconducting magnetic minimum trap, enabled us to carry out a high-sensitivity and low-background search for trapped synthesised antihydrogen atoms. We aim to identify the annihilations of antihydrogen atoms held for at least 130 ms in the trap before being released over ~30 ms. After a three-week experimental run in 2009 involving mixing of 107 antiprotons with 1.3ᅵ109 positrons to produce 6ᅵ105 antihydrogen atoms, we have identified six antiproton annihilation events that are consistent with the release of trapped antihydrogen. The cosmic ray background, estimated to contribute 0.14 counts, is incompatible with this observation at a significance of 5.6 sigma. Extensive simulations predict that an alternative source of annihilations, the escape of mirror-trapped antiprotons, is highly unlikely, though this possibility has not yet been ruled out experimentally.

  • 17. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Carpenter, P. T.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Hurt, J. L.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    Autoresonant Excitation of Antiproton Plasmas2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, no 2, p. 025002-Article in journal (Refereed)
    Abstract [en]

    We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination

  • 18. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jenkins, M. J.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jorgensen, L. V.
    Kurchaninov, L.
    Madsen, N.
    McKenna, J. T. K.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sampson, J.
    Sarid, E.
    Seddon, D.
    el Nasr, S. Seif
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    Thornhill, J.
    Wells, D.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    The ALPHA-detector: Module Production and Assembly2012In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, p. C01051-Article in journal (Refereed)
    Abstract [en]

    ALPHA is one of the experiments situated at CERN's Antiproton Decelerator (AD). A Silicon Vertex Detector (SVD) is placed to surround the ALPHA atom trap. The main purpose of the SVD is to detect and locate antiproton annihilation events by means of the emitted charged pions. The SVD system is presented with special focus given to the design, fabrication and performance of the modules.

  • 19. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jenkins, M. J.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jorgensen, L. V.
    Kurchaninov, L.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Nasr, S. Seif el
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    Trapped antihydrogen2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 468, no 7324, p. 673-676Article in journal (Refereed)
    Abstract [en]

    Antimatter was first predicted1 in 1931, by Dirac. Work with high-energy antiparticles is now commonplace, and anti-electrons are used regularly in the medical technique of positron emission tomography scanning. Antihydrogen, the bound state of an antiproton and a positron, has been produced2, 3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. The charge conjugation/parity/time reversal (CPT) theorem, a crucial part of the foundation of the standard model of elementary particles and interactions, demands that hydrogen and antihydrogen have the same spectrum. Given the current experimental precision of measurements on the hydrogen atom (about two parts in 1014 for the frequency of the 1s-to-2s transition4), subjecting antihydrogen to rigorous spectroscopic examination would constitute a compelling, model-independent test of CPT. Antihydrogen could also be used to study the gravitational behaviour of antimatter5. However, so far experiments have produced antihydrogen that is not confined, precluding detailed study of its structure. Here we demonstrate trapping of antihydrogen atoms. From the interaction of about 107 antiprotons and 7 × 108 positrons, we observed 38 annihilation events consistent with the controlled release of trapped antihydrogen from our magnetic trap; the measured background is 1.4 ± 1.4 events. This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.

  • 20. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Lambo, R.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wilding, D.
    Wurtele, J. S.
    Yamazaki, Y.
    Evaporative Cooling of Antiprotons to Cryogenic Temperatures2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 1, p. 013003-Article in journal (Refereed)
    Abstract [en]

    We report the application of evaporative cooling to clouds of trapped antiprotons, resulting in plasmas with measured temperature as low as 9 K. We have modeled the evaporation process for charged particles using appropriate rate equations. Good agreement between experiment and theory is observed, permitting prediction of cooling efficiency in future experiments. The technique opens up new possibilities for cooling of trapped ions and is of particular interest in antiproton physics, where a precise CPT test on trapped antihydrogen is a long-standing goal.

  • 21. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kemp, S. L.
    Kurchaninov, L.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Pusa, P.
    Rasmussen, C. O.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Wurtele, J. S.
    Yamazaki, Y.
    Confinement of antihydrogen for 1,000 seconds2011In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 7, no 7, p. 558-564Article in journal (Refereed)
    Abstract [en]

    Atoms made of a particle and an antiparticle are unstable, usually surviving less than a microsecond. Antihydrogen, made entirely of antiparticles, is believed to be stable, and it is this longevity that holds the promise of precision studies of matter-antimatter symmetry. We have recently demonstrated trapping of antihydrogen atoms by releasing them after a confinement time of 172 ms. A critical question for future studies is: how long can anti-atoms be trapped? Here, we report the observation of anti-atom confinement for 1,000 s, extending our earlier results by nearly four orders of magnitude. Our calculations indicate that most of the trapped anti-atoms reach the ground state. Further, we report the first measurement of the energy distribution of trapped antihydrogen, which, coupled with detailed comparisons with simulations, provides a key tool for the systematic investigation of trapping dynamics. These advances open up a range of experimental possibilities, including precision studies of charge-parity-time reversal symmetry and cooling to temperatures where gravitational effects could become apparent.

  • 22. Andresen, G. B.
    et al.
    Ashkezari, M. D.
    Bertsche, W.
    Bowe, P. D.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Deller, A.
    Eriksson, S.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Gutierrez, A.
    Hangst, J. S.
    Hardy, W. N.
    Hayden, M. E.
    Hayano, R. S.
    Humphries, A. J.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jorgensen, L. V.
    Kurchaninov, L.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Sarid, E.
    el Nasr, S. Seif
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    van der Werf, D. P.
    Yamazaki, Y.
    Antihydrogen annihilation reconstruction with the ALPHA silicon detector2012In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 684, p. 73-81Article in journal (Refereed)
    Abstract [en]

    The ALPHA experiment has succeeded in trapping antihydrogen, a major milestone on the road to spectroscopic comparisons of antihydrogen with hydrogen. An annihilation vertex detector, which determines the time and position of antiproton annihilations, has been central to this achievement. This detector, an array of double-sided silicon microstrip detector modules arranged in three concentric cylindrical tiers, is sensitive to the passage of charged particles resulting from antiproton annihilation. This article describes the method used to reconstruct the annihilation location and to distinguish the annihilation signal from the cosmic ray background. Recent experimental results using this detector are outlined.

  • 23. Butler, E.
    et al.
    Andresen, G.
    Ashkezari, M.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P.
    Bray, C.
    Cesar, C.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M.
    Gill, D.
    Hangst, J.
    Hardy, W.
    Hayano, R.
    Hayden, M.
    Humphries, A.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kurchaninov, L.
    Lambo, R.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D.
    So, C.
    Storey, J.
    Thompson, R.
    van der Werf, D.
    Wilding, D.
    Wurtele, J.
    Yamazaki, Y.
    Towards antihydrogen trapping and spectroscopy at ALPHA2011In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 199, no 1, p. 39-48Article in journal (Refereed)
    Abstract [en]

    Spectroscopy of antihydrogen has the potential to yield high-precision tests of the CPT theorem and shed light on the matter-antimatter imbalance in the Universe. The ALPHA antihydrogen trap at CERN’s Antiproton Decelerator aims to prepare a sample of antihydrogen atoms confined in an octupole-based Ioffe trap and to measure the frequency of several atomic transitions. We describe our techniques to directly measure the antiproton temperature and a new technique to cool them to below 10 K. We also show how our unique position-sensitive annihilation detector provides us with a highly sensitive method of identifying antiproton annihilations and effectively rejecting the cosmic-ray background.

  • 24. Charlton, M
    et al.
    Andresen, G B
    Ashkezari, M D
    Baquero-Ruiz, M
    Bertsche, W
    Bowe, P D
    Bray, C C
    Butler, E
    Cesar, C L
    Chapman, S
    Fajans, J
    Friesen, T
    Fujiwara, M C
    Gill, D R
    Hangst, J S
    Hardy, W N
    Hayano, R S
    Hayden, M E
    Humphries, A J
    Hydomako, R
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    JÞrgensen, L V
    Kerrigan, S J
    Kurchaninov, L
    Lambo, R
    Madsen, N
    Menary, S
    Nolan, P
    Olchanski, K
    Povilus, A
    Pusa, P
    Robicheaux, F
    Sarid, E
    Nasr, S Seif El
    Silveira, D M
    So, C
    Storey, J W
    Thompson, R I
    Werf, D P Van Der
    Wilding, D
    Wurtele, J S
    Yamazaki, Y
    Collaboration, Alpha
    Antiparticle sources for antihydrogen production and trapping2011In: Journal of Physics: Conference Series, Vol. 262, p. 012001-Article in journal (Refereed)
    Abstract [en]

    Sources of positrons and antiprotons that are currently used for the formation of antihydrogen with low kinetic energies are reviewed, mostly in the context of the ALPHA collaboration and its predecessor ATHENA. The experiments were undertaken at the Antiproton Decelerator facility, which is located at CERN. Operations performed on the clouds of antiparticles to facilitate their mixing to produce antihydrogen are described. These include accumulation, cooling and manipulation. The formation of antihydrogen and some of the characteristics of the anti-atoms that are created are discussed. Prospects for trapping antihydrogen in a magnetic minimum trap, as envisaged by the ALPHA collaboration, are reviewed.

  • 25. Charman, A. E.
    et al.
    Amole, C.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Zhmoginov, A. I.
    Description and first application of a new technique to measure the gravitational mass of antihydrogen2013In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, article id 1785Article in journal (Refereed)
    Abstract [en]

    Physicists have long wondered whether the gravitational interactions between matter and antimatter might be different from those between matter and itself. Although there are many indirect indications that no such differences exist and that the weak equivalence principle holds, there have been no direct, free-fall style, experimental tests of gravity on antimatter. Here we describe a novel direct test methodology; we search for a propensity for anti-hydrogen atoms to fall downward when released from the ALPHA antihydrogen trap. In the absence of systematic errors, we can reject ratios of the gravitational to inertial mass of antihydrogen 475 at a statistical significance level of 5%; worst-case systematic errors increase the minimum rejection ratio to 110. A similar search places somewhat tighter bounds on a negative gravitational mass, that is, on antigravity. This methodology, coupled with ongoing experimental improvements, should allow us to bound the ratio within the more interesting near equivalence regime.

  • 26. Dion, Claude M.
    et al.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Kastberg, Anders
    Sjölund, Peder
    Bimodal momentum distribution of laser-cooled atoms in optical lattices2016In: Physical Review A, ISSN 2469-9926, Vol. 93, no 5, article id 053416Article in journal (Refereed)
    Abstract [en]

    We study, numerically and experimentally, the momentum distribution of atoms cooled in optical lattices. Using semiclassical simulations, we show that this distribution is bimodal, made up of a central feature corresponding to cold, trapped atoms, with tails of hot, untrapped atoms, and that this holds true also for very shallow potentials. Careful analysis of the distribution of high-momentum untrapped atoms, both from simulations and experiments, shows that the tails of the distribution do not follow a normal law, hinting at a power-law distribution and nonergodic behavior. We also revisit the phenomenon leading to the existence of an optimal cooling point, i.e., a potential depth below which the temperature of the atoms starts increasing.

  • 27.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Collisions involving antiprotons and antihydrogen: an overview2018In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 376, no 2116, article id 20170271Article, review/survey (Refereed)
    Abstract [en]

    I give an overview of experimental and theoretical results for antiproton and antihydrogen scattering with atoms and molecules (in particular H, He). At low energies (less than or similar to 1 keV) there are practically no experimental data available. Instead I compare the results from different theoretical calculations, of various degrees of sophistication. At energies up to a few tens of eV, I focus on simple approximations that give reasonably accurate results, as these allow quick estimates of collision rates without embarking on a research project. This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'.

  • 28.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Armour, E. A. G.
    Plummer, M.
    Liu, Y.
    Todd, A. C.
    Helium-antihydrogen scattering at low energies2012In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, p. 035013-Article in journal (Refereed)
    Abstract [en]

    We calculate cross sections for helium-antihydrogen scattering for energies up to 0.01 atomic unit. Our calculation includes elastic scattering, direct antiproton-alpha particle annihilation and rearrangement into He(+)p(-) and ground-state positronium. Elastic scattering is calculated within the Born-Oppenheimer approximation using the potential calculated by Strasburger et al (2005 J. Phys. B: At. Mol. Opt. Phys. 38 3091). Matrix elements for rearrangement are calculated using the T-matrix in the distorted wave approximation, with the initial state represented by Hylleraas-type functions. The strong force, leading to direct annihilation, was included as a short-range boundary condition in terms of the strong-force scattering length.

  • 29.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Charlton, M.
    Formation of antihydrogen beams from positron-antiproton interactions2019In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, article id 073020Article in journal (Refereed)
    Abstract [en]

    The formation of a beam of antihydrogen atoms when antiprotons pass through cold, dense positron plasmas is simulated for various plasma properties and antiproton injection energies. There are marked dependences of the fraction of injected antiprotons which are emitted as antihydrogen in a beam-like configuration upon the temperature of the positrons, and upon the antiproton kinetic energy. Yields as high as 13% are found at the lowest positron temperatures simulated here (5K) and at antiproton kinetic energies below about 0.1 eV. By 1 eV the best yields are as low as 10(-3), falling by about two orders of magnitude with an increase of the positron temperature to 50 K. Example distributions for the antihydrogen angular emission, binding energy and kinetic energy are presented and discussed. Comparison is made with experimental information, where possible.

  • 30.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Charlton, M.
    On the formation of trappable antihydrogen2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 043049Article in journal (Refereed)
    Abstract [en]

    The formation of antihydrogen atoms from antiprotons injected into a positron plasma is simulated, focussing on the fraction that fulfil the conditions necessary for confinement of anti-atoms in a magnetic minimum trap. Trapping fractions of around 10(-4) are found under conditions similar to those used in recent experiments, and in reasonable accord with their results. We have studied the behaviour of the trapped fraction at various positron plasma densities and temperatures and found that collisional effects play a beneficial role via a redistribution of the antihydrogen magnetic moment, allowing enhancements of the yield of low-field seeking states that are amenable to trapping.

  • 31.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Charlton, M.
    van der Werf, D. P.
    The role of antihydrogen formation in the radial transport of antiprotons in positron plasmas2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 13, article id 134004Article in journal (Refereed)
    Abstract [en]

    Simulations have been performed of the radial transport of antiprotons in positron plasmas under ambient conditions typical of those used in antihydrogen formation experiments. The parameter range explored includes several positron densities and temperatures, as well as two different magnetic fields (1 and 3 T). Computations were also performed in which the antihydrogen formation process was artificially suppressed in order to isolate its role from other collisional sources of transport. The results show that, at the lowest positron plasma temperatures, repeated cycles of antihydrogen formation and destruction are the dominant source of radial (cross magnetic field) transport, and that the phenomenon is an example of anomalous diffusion.

  • 32.
    Jonsell, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    van der Werf, D. P.
    Charlton, M.
    Metastable states in antihydrogen formation2014In: Hyperfine interactions, 2014, Vol. 228, no 1-3, p. 81-83Conference paper (Refereed)
    Abstract [en]

    Formation of antihydrogen atoms from antiprotons immersed in a positron plasma is simulated. Special attention is devoted to the role of metastable states, arising from the near conservation of the energy stored in the cyclotron motion of the positrons. We find that the decay of such states changes the density scaling of the formation rate.

  • 33. Madsen, N
    et al.
    Andresen, G B
    Ashkezari, M D
    Baquero-Ruiz, M
    Bertsche, W
    Bowe, P D
    Bray, C C
    Butler, E
    Cesar, C L
    Chapman, S
    Charlton, M
    Fajans, J
    Friesen, T
    Fujiwara, M C
    Gill, D R
    Hangst, J S
    Hardy, W N
    Hayden, M R
    Humphries, A J
    Hydomako, R
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Jørgensen, L V
    Kurchaninov, L
    Lambo, R
    Menary, S
    Nolan, P
    Olchanski, K
    Olin, A
    Povilus, A
    Pusa, P
    Robicheaux, F
    Sarid, E
    Seif El Nasr, S
    Silveira, D M
    So, C
    Storey, J W
    Thompson, R I
    van der Werf, D P
    Wurtele, J S
    Yamazaki, Y
    Search for trapped antihydrogen in ALPHA2011In: Canadian journal of physics (Print), ISSN 0008-4204, E-ISSN 1208-6045, Vol. 89, no 1, p. 7-16Article in journal (Refereed)
    Abstract [en]

    Antihydrogen spectroscopy promises precise tests of the symmetry of matter and antimatter, and can possibly offer new insights into the baryon asymmetry of the universe. Antihydrogen is, however, difficult to synthesize and is produced only in small quantities. The ALPHA collaboration is therefore pursuing a path towards trapping cold antihydrogen to permit the use of precision atomic physics tools to carry out comparisons of antihydrogen and hydrogen. ALPHA has addressed these challenges. Control of the plasma sizes has helped to lower the influence of the multipole field used in the neutral atom trap, and thus lowered the temperature of the created atoms. Finally, the first systematic attempt to identify trapped antihydrogen in our system is discussed. This discussion includes special techniques for fast release of the trapped anti-atoms, as well as a silicon vertex detector to identify antiproton annihilations. The silicon detector reduces the background of annihilations, including background from antiprotons that can be mirror trapped in the fields of the neutral atom trap. A description of how to differentiate between these events and those resulting from trapped antihydrogen atoms is also included.

  • 34. Madsen, N.
    et al.
    Robicheaux, F.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Antihydrogen trapping assisted by sympathetically cooled positrons2014In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, p. 063046-Article in journal (Refereed)
    Abstract [en]

    Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of nature ' s fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of similar to 0.5 K k(B). In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.

  • 35.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    A search for resonances in the p mu e system2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 17, article id 175003Article in journal (Refereed)
    Abstract [en]

    The charge radius of the proton has recently been determined from 2s-2p spectroscopy of muonic hydrogen, giving a result which significantly deviates from earlier measurements. One hypothesis is that this discrepancy could arise because a metastable p mu e state is formed under the p mu (2s) threshold. We search for such a state by considering the three-body pex and p mu x systems, where x is a particle with charge -e and a mass which is varied between the electron and muon mass. We identify a new class of resonances, which extends the mass range allowing formation of resonances compared to an earlier work. We conclude that no p mu e resonances relevant for 2s-2p spectroscopy in muonic hydrogen can exist.

  • 36.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Natural and unnatural parity resonance states in positron-hydrogen scattering2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 22, article id 225001Article in journal (Refereed)
    Abstract [en]

    We present an investigation of resonances with natural and unnatural parities in positron scattering with atomic hydrogen. The complex scaling method has been used. Resonance states for natural parity pi=(-1)(J) with total angular momenta J = 0 - 2 and unnatural parity pi = (-1)(J+1) with J = 1, 2 are calculated. Resonance energies and widths are reported and compared with other theoretical calculations.

  • 37.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Positronium-dipole induced resonances in e(+)-H and e(+)-alkali systems2017In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 50, no 4, article id 044001Article in journal (Refereed)
    Abstract [en]

    We derive general universal scaling relations governing resonances induced by the dipole moment of excited positronium interacting with atomic ions. A single non-universal parameter, which contains all the system-dependent information, is defined. Our results are compared to numerical calculations, using complex scaling, for S, P, and D-wave resonances below the positronium n. =. 2 threshold in the e(+)-(H, Li, Na, K) systems. The energy and width ratios of the successive resonances are found to agree well with the analytically derived scaling law.

  • 38.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Positronium-dipole induced resonances in e$^{+}$-H and e$^{+}$-alkali systemsIn: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455Article in journal (Refereed)
  • 39.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Resonances in a positron-lithium (e(+)-Li) system2016In: Physical Review A, ISSN 2469-9926, Vol. 93, no 5, article id 052707Article in journal (Refereed)
    Abstract [en]

    The method of complex scaling is used to calculate S- and P-wave resonance energies and widths below the Li(3s, 3p, 4s, 4p) excitation thresholds and positronium n = 2 formation threshold in the positron-lithium system. We use two different types of model potentials to determine the interaction between the core and the valence electron. Explicitly correlated Gaussian basis functions are used to represent the correlation effects between the valence electron, the positron, and the Li+ core. A dipole series of resonances are found under the positronium n = 2 threshold. Furthermore, these resonances are found to agree well with an analytically derived scaling law. The present results are compared with those in the literature.

  • 40.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Resonances in positron-potassium ($e^{+}$-K) system with natural and unnatural parities2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 1, article id 015004Article in journal (Refereed)
    Abstract [en]

    We present an investigation of resonances with natural and unnatural parities in the positron-potassium system using the complex scaling method. A model potential is used to represent the interaction between the core and the valence electron. Explicitly correlated Gaussian wave functions are used to represent the correlation effects between the valence electron, the positron and the K+ core. Resonance energies and widths for two partial waves (S- and P-wave) below the K(4p, 5s, 5p, 4d, 4f) excitation thresholds and positronium n = 2 formation threshold are calculated for natural parity. Resonance states for P-e below the K(4d) excitation threshold and positronium n = 2, 3 formation thresholds are calculated for unnatural parity which has not been previously reported. Below both positronium thresholds we have found a dipole series of resonances, with binding energies scaling in good agreement with exceptions from an analytical calculation. The present results are compared with those in the literature.

  • 41.
    Umair, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Resonances with natural and unnatural parities in positron-sodium scattering2015In: Physical Review A, ISSN 2469-9926, Vol. 92, article id 012706Article in journal (Refereed)
    Abstract [en]

    We present an investigation of resonances in positron-sodium scattering using the complex scaling method. For the target sodium atoms, the interaction between the core and outer electron is treated using two different types of analytical model potentials. Explicitly correlated Gaussian wave functions are used to represent the correlation effects between the outer electron, the positron, and the Na+ core. S-, P-, and D-wave resonances with natural parity have been calculated for energies extending up to the positronium n = 2 formation threshold. Resonance states for unnatural parities Pe and D0 have been calculated for energies extending up to the positronium n = 3 threshold. Below both positronium thresholds we have for each symmetry identified a dipole series of resonances, with binding energies scaling in good agreement with expectations from an analytical calculation. The presented results are compared with other theoretical calculations.

  • 42. Van Der Werf, D. P.
    et al.
    Andresen, G. B.
    Ashkezari, M. D.
    Baquero-Ruiz, M.
    Bertsche, W.
    Bowe, P. D.
    Bray, C. C.
    Butler, E.
    Cesar, C. L.
    Chapman, S.
    Charlton, M.
    Fajans, J.
    Friesen, T.
    Fujiwara, M. C.
    Gill, D. R.
    Hangst, J. S.
    Hardy, W. N.
    Hayano, R. S.
    Hayden, M. E.
    Humphries, A. J.
    Hydomako, R.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics. Swansea University, United Kingdom.
    Jørgensen, L. V.
    Kurchaninov, L.
    Lambo, R.
    Madsen, N.
    Menary, S.
    Nolan, P.
    Olchanski, K.
    Olin, A.
    Povilus, A.
    Pusa, P.
    Robicheaux, F.
    Sarid, E.
    Silveira, D. M.
    So, C.
    Storey, J. W.
    Thompson, R. I.
    Wurtele, J. S.
    Yamazaki, Y.
    Antimatter transport processes2010In: AAPS Journal, ISSN 1550-7416, E-ISSN 1550-7416, Vol. 257, no 1, article id 012004Article in journal (Refereed)
    Abstract [en]

    A comparison of the 1S-2S transitions of hydrogen and antihydrogen will yield a stringent test of CPT conservation. Necessarily, the antihydrogen atoms need to be trapped to perform high precision spectroscopy measurements. Therefore, an approximately 0.75 T deep neutral atom trap, equivalent to about 0.5 K for ground state (anti)hydrogen atoms, has been superimposed on a Penning-Malmberg trap in which the anti-atoms are formed. The antihydrogen atoms are produced following a number of steps. A bunch of antiprotons from the CERN Antiproton Decelerator is caught in a Penning-Malmberg trap and subsequently sympathetically cooled and then compressed using rotating wall electric fields. A positron plasma, formed in a separate accumulator, is transported to the main system and also compressed. Antihydrogen atoms are then formed by mixing the antiprotons and positrons. The velocity of the anti-atoms, and their binding energies, will strongly depend on the initial conditions of the constituent particles, for example their temperatures and densities, and on the details of the mixing process. In this paper the complete lifecycle of antihydrogen atoms will be presented, starting with the production of the constituent antiparticles and the description of the manipulations necessary to prepare them appropriately for antihydrogen formation. The latter will also be described, as will the possible fates of the anti-atoms.

  • 43. Zammit, Mark C.
    et al.
    Charlton, Michael
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Colgan, James
    Savage, Jeremy S.
    Fursa, Dmitry
    Kadyrov, Alisher S.
    Bray, Igor
    Forrey, Robert C.
    Fontes, Christopher J.
    Leiding, Jeffery A.
    Kilcrease, David P.
    Hakel, Peter
    Timmermans, Eddy
    Laser-driven production of the antihydrogen molecular ion2019In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 100, no 4, article id 042709Article in journal (Refereed)
    Abstract [en]

    The feasibility of producing the molecular antihydrogen anion (H) over bar (-)(2) in the laboratory is investigated. Utilizing reaction rates calculated here involving the interaction of laser excited-state antihydrogen atoms held in magnetic minimum traps, key processes are identified that could lead to anion production, as well as competing effects leading to anti-atom loss. These are discussed in the context of present-day and near-future experimental capabilities.

  • 44. Zelan, M.
    et al.
    Hagman, H.
    Labaigt, G.
    Jonsell, Svante
    Stockholm University, Faculty of Science, Department of Physics.
    Dion, C. M.
    Experimental measurement of efficiency and transport coherence of a cold-atom Brownian motor in optical lattices2011In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, no 2, p. 020102-Article in journal (Refereed)
    Abstract [en]

    The rectification of noise into directed movement or useful energy is utilized by many different systems. The peculiar nature of the energy source and conceptual differences between such Brownian motor systems makes a characterization of the performance far from straightforward. In this work, where the Brownian motor consists of atoms interacting with dissipative optical lattices, we adopt existing theory and present experimental measurements for both the efficiency and the transport coherence. We achieve up to 0.3% for the efficiency and 0.01 for the Peclet number.

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