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  • 1. Aad, G.
    et al.
    Abbott, B.
    Abdallah, J.
    Gellerstedt, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Measurement of the top quark pair production cross section with ATLAS in pp collisions at √s = 7 TeV in dilepton final states2011Report (Other academic)
    Abstract [en]

    A measurement is presented of the production cross section of top quark pairs (σ_{\ttbar{}}) in proton-proton (pp) collisions at √s = 7 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. Using a data sample of 35 pb−1, candidate events are selected in the dilepton topology with large missing transverse energy, \met{}, and at least two jets.

    A baseline analysis employing kinematic properties of the candidate events to separate the signal from background and using data-driven techniques to determine the most important backgrounds, results in a measurement ofσ_{\ttbar{}} = 173 ± 22(stat.)+18 −16(syst.)+8 −7(lum.) pb,

    where the three uncertainties are from statistics, systematics and integrated luminosity, respectively.

    We also perform a cross section measurement requiring at least one b-tagged jet and a looser kinematic selection that increases the signal-to-background ratio, yielding

    σ_{\ttbar{}} = 171 ± 22(stat.)+21 -16(syst.)+7 −6(lum.) pb.

    Additional studies are performed to corroborate these measurements; a technique that normalizes the \ttbar{} signal yield to the measured rate of Z decays, a two-dimensional template shape fit using the \met{} vs the number of jets to simultaneously measure the production cross sections of \ttbar{}, WW and Z → ττ final states, and a simultaneous measurement of σ_{\ttbar{}} and the b-tagging efficiency using the distribution of the number of tagged jets in each event.

    All the measurements are in good agreement with each other and the Standard Model prediction.

  • 2. Aad, G.
    et al.
    Åsman, Barbro
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Clément, Christophe
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Gellerstedt, Karl
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hellman, Sten
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hidvégi, Attila
    Stockholm University, Faculty of Science, Department of Physics.
    Holmgren, Sven-Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Johansen, Marianne
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, K. Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lesser, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Milstead, David A.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Moa, Torbjörn
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nordkvist, Björn
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ohm, Christian C.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ramstedt, Magnus
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Selldén, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Silverstein, Samuel B.
    Stockholm University, Faculty of Science, Department of Physics.
    Sjölin, Jörgen
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tylmad, Maja
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yang, Zhaoyu
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zutshi, V.
    Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the ATLAS Detector at the LHC2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 16, 161801- p.Article in journal (Refereed)
    Abstract [en]

    A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated luminosity of 315 nb(-1) collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% C. L. the q* mass interval 0: 30< m(q)*< 1:26 TeV, extending the reach of previous experiments.

  • 3. Abazov, V. M.
    et al.
    Abbott, B.
    Abolins, M.
    Åsman, Barbro
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Events with Leptonic Jets and Missing Transverse Energy in p(p)over-bar Collisions at root s=1.96 TeV2010In: Physical Review Letters, ISSN 0031-9007, Vol. 105, no 21, 211802- p.Article in journal (Refereed)
    Abstract [en]

    We present the first search for pair production of isolated jets of charged leptons in association with a large imbalance in transverse energy in pp̅ collisions using 5.8  fb-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. No excess is observed above the standard model background, and the result is used to set upper limits on the production cross section of pairs of supersymmetric chargino and neutralino particles as a function of “dark-photon” mass, where the dark photon is produced in the decay of the lightest supersymmetric particle

  • 4. Abazov, V. M.
    et al.
    Abbott, B.
    Abolins, M.
    Åsman, Barbro
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Sneutrino Production in e mu Final States in 5.3 fb(-1) of p(p)over-bar Collisions at root s = 1.96 TeV2010In: Physical Review Letters, ISSN 0031-9007, Vol. 105, no 19, 191802- p.Article in journal (Refereed)
    Abstract [en]

    We report the results of a search for R parity violating (RPV) interactions leading to the production of supersymmetric sneutrinos decaying into eμ final states using 5.3  fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Having observed no evidence for production of eμ resonances, we set direct bounds on the RPV couplings λ311 and λ312 as a function of sneutrino mass.

  • 5. Abdo, A, et al
    et al.
    Axelsson, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Meurer, Christine
    Stockholm University, Faculty of Science, Department of Physics.
    Sellerholm, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    The Fermi/LAT Collaboration,
    Measurement of the Cosmic Ray e++e- Spectrum from 20GeV to 1TeV with the Fermi Large Area Telescope2009In: Physical Review Letters, ISSN 0031-9007, Vol. 102, no 18Article in journal (Refereed)
    Abstract [en]

    Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2m2sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.

  • 6.
    Abulaiti, Yiming
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Direct Top Squark Pair Production with the ATLAS Experiment and Studies of the Primary Vertex Reconstruction Performance2014Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The ATLAS detector is one of the two largest experiments installed at the Large Hadron Collider at CERN, the European Organization for Nuclear Research. During the first run, the ATLAS detector recorded data at centre of mass energies of 7 TeV and 8 TeV, enabling many precision measurements and new physics searches. One important task in ATLAS is measuring the primary vertex, the interaction point of the hardest proton-proton collision in an event. In this thesis, a study of the primary vertex reconstruction performance in data and simulated events using $t\bar{t}$ and ${Z}$ events is presented. Within the statistics available, the performance in data and simulated events is found to be compatible. Motivated by the limitations of the Standard Model of particle physics, searches for supersymmetric particles are performed with the ATLAS experiment. No signal has been observed so far, and the results are used to set exclusion limits on the masses of the supersymmetric particles. As the exclusion limits are derived from analyses which each target only a single decay mode of a supersymmetric particle, the analyses might have lower sensitivity to more complex decay scenarios. In this thesis the sensitivity of one of the ATLAS searches for direct top squark pair production to models with more complex decay modes is investigated. The study concludes that the sensitivity to models where the top squark can decay via heavier charginos and neutralinos is lower than the sensitivity to models where only decays to the lightest chargino or neutralino are present.

  • 7.
    Abulaiti, Yiming
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Pair-Produced Supersymmetric Top Quark Partners with the ATLAS Experiment2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Searches for the supersymmetric partner of the top quark (stop) are motivated by natural supersymmetry, where the stop has to be light to cancel the large radiative corrections to the Higgs boson mass. This thesis presents three different searches for the stop at √s = 8 TeV and √s = 13 TeV using data from the ATLAS experiment at CERN’s Large Hadron Collider. The thesis also includes a study of the primary vertex reconstruction performance in data and simulation at √s = 7 TeV using tt and Z events. All stop searches presented are carried out in final states with a single lepton, four or more jets and large missing transverse energy. A search for direct stop pair production is conducted with 20.3 fb−1 of data at a center-of-mass energy of √s = 8 TeV. Several stop decay scenarios are considered, including those to a top quark and the lightest neutralino and to a bottom quark and the lightest chargino. The sensitivity of the analysis is also studied in the context of various phenomenological MSSM models in which more complex decay scenarios can be present. Two different analyses are carried out at √s = 13 TeV. The first one is a search for both gluino-mediated and direct stop pair production with 3.2 fb−1 of data while the second one is a search for direct stop pair production with 13.2 fb−1 of data in the decay scenario to a bottom quark and the lightest chargino. The results of the analyses show no significant excess over the Standard Model predictions in the observed data. Consequently, exclusion limits are set at 95% CL on the masses of the stop and the lightest neutralino.

  • 8.
    Adiels, L
    et al.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Cooper, M. D.
    Institute for Physics, University of Basle.
    Findeisen, C.
    Institute for Physics, University of Basle.
    Hatzifotiadou, D.
    Hugi, M
    Institute for Physics, University of Basle.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Meyer, M.
    Kernforschungszentrum, Universität Karlsruche.
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Papastefanou, C
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Tröster, D.
    Institute for Physics, University of Basle.
    Williams, M. C. S.
    Institute for Physics, University of Basle.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Some results of experiment PS182 at LEAR1986In: Antiproton 86  : VIII European symposium on nucleon-antinucleon interactions, 1-5 September 1986, Singspore: World Scientific Publishing , 1986, 199-204 p.Conference paper (Other academic)
  • 9.
    Adiels, L
    et al.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Cooper, M. D.
    Institute for Physics, University of Basle.
    Findeisen, C.
    Institute for Physics, University of Basle.
    Hatzifotiadou, D.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Kuzminski, J
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Tröster, D.
    Institute for Physics, University of Basle.
    Williams, M. C. S.
    Institute for Physics, University of Basle.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    π0 and η spectroscopy at LEAR1985In: Physics with antiprotons at LEAR in the ACOL era: proceedings of the Third LEAR Workshop, Tignes, Savoie, France, January 19-26, 1985 / [ed] U. Gastaldi et al, Gif sur Yvette: Editions Frontières , 1985, 359-360 p.Conference paper (Other academic)
  • 10.
    Adiels, L
    et al.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Cooper, M. D.
    Institute for Physics, University of Basle.
    Findeisen, C.
    Institute for Physics, University of Basle.
    Hatzifotiadou, D.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Papastefanou, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Tröster, D.
    Institute for Physics, University of Basle.
    Williams, M. C. S.
    Institute for Physics, University of Basle.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Investigations on baryonium and other rare ptoton-antiproton annihilation modes using pi0 and eta spectroscopy1986In: Proceedings of the 2nd Hellenic School on Elementary Particle Physics, Corfu, Greece, 1-20 September, 1985 / [ed] E. N. Argyres, G. Zoupanos, Singapore: World Scientific , 1986, 51-60 p.Conference paper (Other academic)
  • 11.
    Adiels, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Cooper, M. D.
    Institute for Physics, University of Basle.
    Findeisen, C.
    Institute for Physics, University of Basle.
    Hatzifotiadou, D.
    Hugi, M.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Meyer, M.
    Kernforschungszentrum, Universität Karlsruche.
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Troester, D.
    Institute for Physics, University of Basle.
    Williams, M. C. S.
    Institute for Physics, University of Basle.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Experimental study of the inclusive η-spectrum from proton-antiproton annihilations at rest in liquid hydrogen1989In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, Vol. 42, 49-58 p.Article in journal (Refereed)
    Abstract [en]

    The inclusive η-momentum spectrum from Mathematical expression annihilations at rest in liquid hydrogen was measured at LEAR. Branching ratios were obtained for Mathematical expression, and ηη(8.1±3.1)×10-5. An upper limit for Mathematical expression of 1.8×10-4 at 95% CL was found. The ratio of the branching ratios is BR(ηρvariant)/BR(ηω)=0.51-0.06+0.20. For the ratio of branching ratios into two pseudoscalar mesons, we have BR(ηπ0)/BR(π0π0)=0.65±0.14, BR(ηη)/BR(π0π0), BR(ηη′)/BR(π0π0) at 95% CL, and BR(ηη)/BR(ηπ0). © 1989 Springer-Verlag.

  • 12.
    Adiels, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Backenstoss, G.
    Institute for Physics, University of Basle.
    Bergström, I.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Carius, S.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Charalambous, S.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Cooper, M. D.
    Institute for Physics, University of Basle.
    Findeisen, C.
    Institute for Physics, University of Basle.
    Hatzifotiadou, D.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Papastefanou, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Troester, D.
    Institute for Physics, University of Basle.
    Williams, M. C. S.
    Institute for Physics, University of Basle.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    A π0 and η spectrometer of lead glass and BGO for momenta up to 1 GeV/c1986In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 244, no 3, 380-390 p.Article in journal (Refereed)
    Abstract [en]

    A spectrometer consisting of two sets of bismuth germanium oxide (BGO) crystals and a lead-glass array has been used to measure the [pi]0 and [eta] momentum spectra produced from proton-antiproton annihilations at rest. We describe the test of the BGO sets in electron beams of energies from 50 to 450 MeV. We discuss the method of construction and calibration of the lead-glass array, as well as procedures to extract the energy and position resolutions for detected photons. A momentum resolution ([sigma]) for [pi]0’s and [eta]’s of 4% and 3%, respectively has been achieved at momenta below 1 GeV/c.

  • 13.
    Akrami, Yashar
    Stockholm University, Faculty of Science, Department of Physics.
    Supersymmetry vis-à-vis Observation: Dark Matter Constraints, Global Fits and Statistical Issues2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Weak-scale supersymmetry is one of the most favoured theories beyond the Standard Model of particle physics that elegantly solves various theoretical and observational problems in both particle physics and cosmology. In this thesis, I describe the theoretical foundations of supersymmetry, issues that it can address and concrete supersymmetric models that are widely used in phenomenological studies. I discuss how the predictions of supersymmetric models may be compared with observational data from both colliders and cosmology. I show why constraints on supersymmetric parameters by direct and indirect searches of particle dark matter are of particular interest in this respect. Gamma-ray observations of astrophysical sources, in particular dwarf spheroidal galaxies, by the Fermi satellite, and recording nuclear recoil events and energies by future ton-scale direct detection experiments are shown to provide powerful tools in searches for supersymmetric dark matter and estimating supersymmetric parameters. I discuss some major statistical issues in supersymmetric global fits to experimental data. In particular, I further demonstrate that existing advanced scanning techniques may fail in correctly mapping the statistical properties of the parameter spaces even for the simplest supersymmetric models. Complementary scanning methods based on Genetic Algorithms are proposed.

  • 14.
    Akrami, Yashar
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Savage, Christopher
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Scott, Pat
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    How well will ton-scale dark matter direct detection experiments constrain minimal supersymmetry?2011In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 4, 012- p.Article in journal (Refereed)
    Abstract [en]

    Weakly interacting massive particles (WIMPs) are amongst the most interesting dark matter (DM) candidates. Many DM candidates naturally arise in theories beyond the standard model (SM) of particle physics, like weak-scale supersymmetry (SUSY). Experiments aim to detect WIMPs by scattering, annihilation or direct production, and thereby determine the underlying theory to which they belong, along with its parameters. Here we examine the prospects for further constraining the Constrained Minimal Supersymmetric Standard Model (CMSSM) with future ton-scale direct detection experiments. We consider ton-scale extrapolations of three current experiments: CDMS, XENON and COUPP, with 1000 kg-years of raw exposure each. We assume energy resolutions, energy ranges and efficiencies similar to the current versions of the experiments, and include backgrounds at target levels. Our analysis is based on full likelihood constructions for the experiments. We also take into account present uncertainties on hadronic matrix elements for neutralino-quark couplings, and on halo model parameters. We generate synthetic data based on four benchmark points and scan over the CMSSM parameter space using nested sampling. We construct both Bayesian posterior PDFs and frequentist profile likelihoods for the model parameters, as well as the mass and various cross-sections of the lightest neutralino. Future ton-scale experiments will help substantially in constraining supersymmetry, especially when results of experiments primarily targeting spin-dependent nuclear scattering are combined with those directed more toward spin-independent interactions.

  • 15.
    Akrami, Yashar
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Savage, Christopher
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Scott, Pat
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Statistical coverage for supersymmetric parameter estimation: a case study with direct detection of dark matter2011In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, no 7, 002- p.Article in journal (Refereed)
    Abstract [en]

    Models of weak-scale supersymmetry offer viable dark matter (DM) candidates. Their parameter spaces are however rather large and complex, such that pinning down the actual parameter values from experimental data can depend strongly on the employed statistical framework and scanning algorithm. In frequentist parameter estimation, a central requirement for properly constructed confidence intervals is that they cover true parameter values, preferably at exactly the stated confidence level when experiments are repeated infinitely many times. Since most widely-used scanning techniques are optimised for Bayesian statistics, one needs to assess their abilities in providing correct confidence intervals in terms of the statistical coverage. Here we investigate this for the Constrained Minimal Supersymmetric Standard Model (CMSSM) when only constrained by data from direct searches for dark matter. We construct confidence intervals from one-dimensional profile likelihoods and study the coverage by generating several pseudo-experiments for two benchmark sets of pseudo-true parameters. We use nested sampling to scan the parameter space and evaluate the coverage for the two benchmarks when either flat or logarithmic priors are imposed on gaugino and scalar mass parameters. We observe both under- and over-coverage, which in some cases vary quite dramatically when benchmarks or priors are modified. We show how most of the variation can be explained as the impact of explicit and implicit priors, where the latter are indirectly imposed by physicality conditions. For comparison, we also evaluate the coverage for Bayesian credible intervals, and (predictably) observe significant under-coverage in those cases.

  • 16. Amsler, C.
    et al.
    Doser, M.
    Antonelli, M.
    Milstead, David
    Stockholm University, Faculty of Science, Department of Physics.
    Review of Particle Physics2008In: Physics Letters B, ISSN 0370-2693, Vol. 667, no 1-5Article, review/survey (Refereed)
    Abstract [en]

    This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

  • 17.
    Backenstoss, G.
    et al.
    Institute for Physics, University of Basle.
    Hasinoff, M.
    Institute for Physics, University of Basle.
    Pavlopoulos, P.
    Institute for Physics, University of Basle.
    Repond, J.
    Institute for Physics, University of Basle.
    Tauscher, L.
    Institute for Physics, University of Basle.
    Trï¿œster, D.
    Institute for Physics, University of Basle.
    Adiels, Lars
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Bergström, Ingmar
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Fransson, Kjell
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Kerek, A.
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Guigas, R.
    Kernforschungszentrum, Universität Karlsruche.
    Koch, H.
    Kernforschungszentrum, Universität Karlsruche.
    Poth, H.
    Kernforschungszentrum, Universität Karlsruche.
    Raich, U.
    Kernforschungszentrum, Universität Karlsruche.
    Richter, B.
    Kernforschungszentrum, Universität Karlsruche.
    Suffert, M.
    Centre de recherches nucléaries and Université Louis Pasteur, Strabourg.
    Zioutas, K.
    Dept. of Nuclear Physics, Univerity of Tessaloniki.
    First Observation of the proton-antiproton Annihilation Channels pi0ω, pi0$η and pi0γ1983In: Helvetica Physica Acta, ISSN 0018-0238, Vol. 56Article in journal (Refereed)
  • 18.
    Baltz, Edward A.
    et al.
    Stanford, USA.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Bringmann, Torsten
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Sellerholm, Alexander
    Stockholm University, Faculty of Science, Department of Physics.
    Pre-launch estimates for GLAST sensitivity to Dark Matter annihilation signals2008In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, Vol. 0807, no 013Article in journal (Refereed)
    Abstract [en]

    We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) for indirectly detecting weakly interacting massive particles (WIMPs) through the γ-ray signal that their pair annihilation produces. WIMPs are among the favorite candidates for explaining the compelling evidence that about 80% of the mass in the Universe is non-baryonic dark matter (DM). They are serendipitously motivated by various extensions of the standard model of particle physics such as supersymmetry and universal extra dimensions (UED). With its unprecedented sensitivity and its very large energy range (20 MeV to more than 300 GeV) the main instrument on board the GLAST satellite, the Large Area Telescope (LAT), will open a new window of discovery. As our estimates show, the LAT will be able to detect an indirect DM signature for a large class of WIMP models given a cuspy profile for the DM distribution. Using the current state of the art Monte Carlo and event reconstruction software developed within the LAT collaboration, we present preliminary sensitivity studies for several possible sources inside and outside the Galaxy. We also discuss the potential of the LAT to detect UED via the electron/positron channel. Diffuse background modeling and other background issues that will be important in setting limits or seeing a signal are presented

  • 19. Bardeen, Marjorie G.
    et al.
    K. Erik, Johansson
    Stockholm University, Faculty of Science, Department of Physics.
    Young, M. Jean
    Particle Physics Outreach to Secondary Education2011In: Annual Review of Nuclear and Particle Science, ISSN 0163-8998, E-ISSN 1545-4134, Vol. 61, 149-170 p.Article in journal (Refereed)
    Abstract [en]

    This review summarizes exemplary secondary education and outreach programs of the particle physics community. We examine programs from the following areas: research experiences, high-energy physics data for students, informal learning for students, instructional resources, and professional development. We report findings about these programs' impact on students and teachers and provide suggestions for practices that create effective programs from those findings. We also include some methods for assessing programs.

  • 20.
    Bargholtz, Chr
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Chernyshev, B.A
    Gerén, L
    Stockholm University, Faculty of Science, Department of Physics.
    Grebenev, V.N
    Gurov, Yu.B
    Karpuhkin, V.S
    Laukhin, I.V
    Martemyanov, B.V
    Matveev, V.A
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Shafigullin, R.R
    Sopov, V.S
    Tegnér, Per-Erik
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics.
    Tagging of η mesons using the pd3Heη reaction near threshold2006In: Instruments and experimental techniques (New York), ISSN 0020-4412, E-ISSN 1608-3180, Vol. 49, no 4, 461-467 p.Article in journal (Refereed)
    Abstract [en]

    A zero-degree spectrometer for tagging η mesons on the CELSIUS/WASA facility is described, and its characteristics are presented. Tagging of η mesons is performed by detecting 3He ions produced by reaction pd3Heη close to the production threshold. The low background level (<2%) is in good agreement with the data obtained earlier on the SATURNE accelerator.

  • 21.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Thöngren-Engblom, Pia
    Stockholm University, Faculty of Science, Department of Physics.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics.
     Double-Pionic Fusion of Nuclear Systems and the ABC Effect: Approaching a Puzzle by Exclusive and Kinematically Complete Measurements2009In: Physical Review Letters, ISSN 0031-9007, Vol. 102, no 5, 052301- p.Article in journal (Refereed)
    Abstract [en]

    The ABC effect—a puzzling low-mass enhancement in the ππ invariant mass spectrum, first observed by Abashian, Booth, and Crowe—is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn→dπ0π0 at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (ππ)I=L=0 channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a ΔΔ system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

  • 22.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Thörngren-Engblom, Pia
    Stockholm University, Faculty of Science, Department of Physics.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics.
     Exclusive measurtement of two-pion production in the dd->4Heππ reaction2009In: Nuclear Physics A, ISSN 0375-9474, Vol. 825, no 1-2, 71-90 p.Article in journal (Refereed)
    Abstract [en]

    The results from the first kinematically complete measurement of the reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar ππ-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low ππ-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NNdπ sub-processes.

  • 23.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Thörngren-Engblom, Pia
    Stockholm University, Faculty of Science, Department of Physics.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics.
     Production of the ω meson in the pd -> 3He ω reaction at 1450 MeV and 1360 MeV2009In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, ISSN ISSN 0556-2813, Vol. 79, no 4, 044002- p.Article in journal (Refereed)
    Abstract [en]

    The production of ω mesons in the pd→3Heω reaction has been studied at two energies near the kinematic threshold, Tp=1450 MeV and Tp=1360 MeV. The differential cross section was measured as a function of the ω c.m. angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections

  • 24.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Single- and double-pion production in nucleon collisions on the nucleon and on nuclei - the ABC effect and its origin in a dibaryonic resonance2008In: Progress in Particle and Nuclear Physics, Vol. 61Article in journal (Refereed)
  • 25.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    The WASA detector facility at CELSIUS2008In: Nuclear Instruments and Methods in Physics Research A, Vol. 594Article in journal (Refereed)
  • 26.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Calén,, H.
    The Svedberg Laboratory, Uppsala, Sweden.
    Ekström,, C.
    The Svedberg Laboratory, Uppsala, Sweden.
    Fransson,, K.
    The Svedberg Laboratory, Uppsala, Sweden.
    Kupsc, À.
    The Svedberg Laboratory, Uppsala, Sweden.
    Marciniewski,, P.
    The Svedberg Laboratory, Uppsala, Sweden.
    Ruber,, R. J. M.Y.
    The Svedberg Laboratory, Uppsala, Sweden.
    Measurement of h meson decays into lepton-antilepton pairs2008In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 77, no 3, 32004-32008 p.Article in journal (Refereed)
    Abstract [en]

    A search for rare lepton decays of the η meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay η→e+e-e+e- events are reported with a background of 1.3±0.2 events. This allows to set an upper limit to the branching ratio of 9.7×10-5 (90% CL). The branching ratio for the decay η→e+e-γ is determined to (7.8±0.5stat±0.8syst)×10-3 in agreement with world average value. An upper limit (90% CL) for the branching ratio for the η→e+e- decay is 2.7×10-5 and a limit for the sum of the η→μ+μ-μ+μ- and η→π+π-μ+μ- decays is 3.6×10-4.

  • 27.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Gerén, Linda
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Kupść, A.
    Department of Nuclear and Particle Physics, Uppsala University.
    Shafigullinc, R.R:
    Moscow Engineering Physics Institute (State University), .
    Properties of the WASA pellet target and a stored intermediate-energy beam2008In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 587, no 2-3, 178-187 p.Article in journal (Refereed)
    Abstract [en]

    Experimental data from the reaction close to threshold have been used to investigate time-dependent properties of the WASA pellet target and the stored beam of 892.8 MeV protons in the CELSIUS accelerator. The detection of 3He ions in solid-state detectors provides an excellent almost background free trigger for η production. Pellet interactions with the surrounding material and with the beam lead to evaporation of deuterium gas into the beam pipe. Approximately 30% of the registered η decay events are due to interactions in deuterium gas outside the pellets. Due to beam–target interaction the beam is transversely heated and appears to acquire a component of a slightly lower energy.

  • 28.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Honn, Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Tegnér, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    Wachtmeister, Staffan
    Stockholm University, Faculty of Science, Department of Physics. kärnfysik.
    A new surface laboratory for measurements of low-level radioactivity2008In: Applied Radiation and Isotopes, Vol. 66Article in journal (Refereed)
  • 29.
    Bargholtz, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Tegner, Per-Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Zartova, Irina
    Stockholm University, Faculty of Science, Department of Physics.
    Jacewicz, M.
    Uppsala University, Uppsala, Sweden.
    Johansson, T
    Uppsala University, Uppsala, Sweden.
    Lindberg, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Keleta, S.
    Uppsala University, Uppsala, Sweden.
    Koch, I.
    Uppsala University, Uppsala, Sweden.
    Kullander, S.
    Uppsala University, Uppsala, Sweden.
    Schönning, K.
    Uppsala University, Uppsala, Sweden.
    Thörngren Engblom, P.
    Uppsala University, Uppsala, Sweden.
    Wolke, M.
    Uppsala University, Uppsala, Sweden.
    Calén, H.
    The Svedberg Laboratory, Uppsala, Sweden.
    Ekström, C.
    The Svedberg Laboratory, Uppsala, Sweden.
    Fransson, K.
    The Svedberg Laboratory, Uppsala, Sweden.
    Marciniewski, P.
    The Svedberg Laboratory, Uppsala, Sweden.
    Ruber, R.J.M.Y.
    The Svedberg Laboratory, Uppsala, Sweden.
    Gustafsson, L.
    Uppsala University, Uppsala, Sweden.
    Höistad, B.
    Uppsala University, Uppsala, Sweden.
    Kupść, A.
    The Svedberg Laboratory, Uppsala, Sweden.
    Measurement of the η -> π+π-e+e- branching ratio2007In: Physics Letters B, ISSN 0370-2693, Vol. 644, no 5-6, 299-303 p.Article in journal (Refereed)
    Abstract [en]

    The reaction at threshold was used to provide a clean source of η mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay ηπ+πe+e is measured to be (4.3±1.3±0.4)×10−4.

  • 30.
    Barnett, R. M.
    et al.
    Lawrence Berkeley National Laboratory, MS 50R-6008, Berkeley, CA 94720, USA.
    Johansson, K. Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Kourkoumelis, C.
    University of Athens, Greece.
    Long, L.
    School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK.
    Pequenao, J.
    Lawrence Berkeley National Laboratory, MS 50R-6008, Berkeley, CA 94720, USA.
    Reimers, C.
    Department of Astronomy, University of Vienna, Austria.
    Watkins, P.
    School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK.
    Learning with the ATLAS experiment at CERN2012In: Physics Education, ISSN 0031-9120, E-ISSN 1361-6552, Vol. 47, no 1, 28-37 p.Article in journal (Refereed)
    Abstract [en]

    With the start of the LHC, the new particle collider at CERN, the ATLAS experiment is also providing high-energy particle collisions for educational purposes. Several education projects—education scenarios—have been developed and tested on students and teachers in several European countries within the Learning with ATLAS@CERN project. These highly appreciated projects could become a new component in many teachers' classrooms. The Learning with ATLAS portal and the information on the ATLAS public website make it possible for teachers to design educational material for their own situations. To be able to work with real data adds a new dimension to particle physics explorations at school.

  • 31.
    Bartos, Imre
    et al.
    Columbia University, New York, USA.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Corsi, Alessandra
    California Institute of Technology, Pasadena, USA.
    Márka, Szabolcs
    Columbia University, New York, USA and Universite Paris Diderot, Paris, France.
    Observational Constraints on Multimessenger Sources of Gravitational Waves and High-Energy Neutrinos2011In: Physical Review Letters, ISSN 0031-9007, Vol. 107, no 25, 251101- p.Article in journal (Refereed)
    Abstract [en]

    Many astronomical sources of intense bursts of photons are also predicted to be strong emitters of gravitational waves (GWs) and high-energy neutrinos (HENs). Moreover some suspected classes, e. g., choked gamma-ray bursts, may only be identifiable via nonphoton messengers. Here we explore the reach of current and planned experiments to address this question. We derive constraints on the rate of GW and HEN bursts based on independent observations by the initial LIGO and Virgo GW detectors and the partially completed IceCube (40-string) HEN detector. We then estimate the reach of joint GW + HEN searches using advanced GW detectors and the completed km(3) IceCube detector to probe the joint parameter space. We show that searches undertaken by advanced detectors will be capable of detecting, constraining, or excluding, several existing models with 1 yr of observation.

  • 32.
    Bee, C. P.
    et al.
    Liverpool University.
    Heyes, G.
    Liverpool University,.
    Sacks, L.
    Liverpool University,.
    Adiels, L
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Tröster, D.
    Institute for Physics, University of Basle.
    Watson, E. J.
    CERN.
    Wendler, H
    The CP-LEAR data acquisition system1986In: Proceedings: VMEbus in physics conference, CERN, Geneva, Switzerland, 7th and 8th October 1985, Geneva: CERN , 1986, 179-184 p.Conference paper (Other academic)
  • 33.
    Bendtz, Katarina
    Stockholm University, Faculty of Science, Department of Physics.
    Studies of triggering and exotic particle searches at ATLAS, and a search for trapped monopoles2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The ATLAS detector at the LHC operated through 2011 and 2012 with 7 and 8 TeV centre-of-mass energy of its colliding proton bunches, respectively. One if its main objectives is to search for physics beyond the Standard Model. This thesis presents a study of a data-driven background method designed for long-lived heavy particles searches, where the signatures are allowed by for example R-parity violating Supersymmetry. Several studies of the perfor- mance of ATLAS trigger system have also been carried out. A contribution to a non-ATLAS search for primordial trapped magnetic monopoles was also undertaken. Data-taking and calibration of a SQUID magnetometer used when searching for magnetic monopoles in volcanic polar rocks were carried out. 

  • 34.
    Bergeås Kuutmann, Elin
    Stockholm University, Faculty of Science, Department of Physics.
    Calibration of the ATLAS calorimeters and discovery potential for massive top quark resonances at the LHC2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    ATLAS is a multi-purpose detector which has recently started to take data at the LHC at CERN. This thesis describes the tests and calibrations of the central calorimeters of ATLAS and outlines a search for heavy top quark pair resonances.The calorimeter tests were performed before the ATLAS detector was assembled at the LHC, in such a way that particle beams of known energy were targeted at the calorimeter modules. In one of the studies presented here, modules of the hadronic barrel calorimeter, TileCal, were exposed to beams of pions of energies between 3 and 9 GeV. It is shown that muons from pion decays in the beam can be separated from the pions, and that the simulation of the detector correctly describes the muon behaviour.

    In the second calorimeter study, a scheme for local hadronic calibration is developed and applied to single pion test beam data in a wide range of energies, measured by the combination of the electromagnetic barrel calorimeter and the TileCal hadronic calorimeter. The calibration method is shown to provide a calorimeter linearity within 3%, and also to give a reasonable agreement between simulations and data.

    The physics analysis of this thesis is the proposed search for heavy top quark resonances, and it is shown that a narrow uncoloured top pair resonance, a Z', could be excluded (or discovered) at 95% CL for cross sections of 4.0±1.6 pb (in the case of M=1.0 TeV/c2) or 2.0±0.3 pb (M=2.0 TeV/c2), including systematical uncertainties in the model, assuming √s = 10 TeV and an integrated luminosity of 200 pb-1. It is also shown that an important systematical uncertainty is the jet energy scale, which further underlines the importance of hadronic calibration.

  • 35.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Clemént, Christoph
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Gellerstedt, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Hellman, Sten
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Holmgren, Sven-Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics.
    Lesser, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Nordkvist, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Ramstedt, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Selldén, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Sjölin, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Tylmad, Maja
    Stockholm University, Faculty of Science, Department of Physics.
    Testbeam Studies of Production Modules of the ATLAS Tile  Calorimeter2009In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 606, 362-394 p.Article in journal (Refereed)
  • 36.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Clément, Christophe
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Gellerstedt, Karl
    Stockholm University, Faculty of Science, Department of Physics.
    Hellman, Sten
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Holmgren, Sven-Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics.
    Lesser, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Nordkvist, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Ramstedt, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Selldén, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Sjölin, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Tylmad, Maja
    Stockholm University, Faculty of Science, Department of Physics.
    Measurement of Pion and Proton Response and Longitudinal Shower Profiles up to 20 Nuclear Interaction Lengths with the ATLAS Tile Calorimeter2010In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 615, no 2, 158-181 p.Article in journal (Refereed)
    Abstract [en]

    The response of pions and protons in the energy range of 20–180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron–scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal shower development for pions and protons up to 20 nuclear interaction lengths. It was found that pions penetrate deeper in the calorimeter than protons. However, protons induce showers that are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal shower profiles are described by an analytical shower parametrization within an accuracy of 5–10%. The amount of energy leaking out behind the calorimeter is determined and parametrized as a function of the beam energy and the calorimeter depth. This allows for a leakage correction of test-beam results in the standard projective geometry.

  • 37.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Milstead, David
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A Layer Correlation Technique for Pion Energy Calibration at the 2004 ATLAS Combined Beam Test2011In: Journal of Instrumentation, ISSN 1748-0221, Vol. 6, P06001- p.Article in journal (Refereed)
    Abstract [en]

    A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.

  • 38.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics.
    Milstead, David
    Stockholm University, Faculty of Science, Department of Physics.
    Combined Performance Studies for Electrons at the 2004 ATLAS Combined Test-Beam2010In: Journal of Instrumentation, ISSN 1748-0221, Vol. 5, P11006- p.Article in journal (Refereed)
  • 39.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Milstead, David
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Photon Reconstruction in the ATLAS Inner Detector and Liquid Argon Barrel Calorimeter at the 2004 Combined Test Beam2011In: Journal of Instrumentation, ISSN 1748-0221, Vol. 6, P04001- p.Article in journal (Refereed)
    Abstract [en]

    The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same simulation and reconstruction tools as those used for the ATLAS detector itself.                   

  • 40.
    Bergeås Kuutmann, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics.
    Milstead, David
    Stockholm University, Faculty of Science, Department of Physics.
    Study of the Response of the ATLAS Central Calorimeter to Pions of Energies from 3 to 9 GeV2009In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 607, 372-386 p.Article in journal (Refereed)
  • 41.
    Bergholtz, Emil Johansson
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Hans
    Stockholm University, Faculty of Science, Department of Physics.
    Hermanns, Maria
    Stockholm University, Faculty of Science, Department of Physics.
    Karlhede, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Microscopic theory of the quantum Hall hierarchy2007In: Physical Review Letters, ISSN 0031-9007, Vol. 99, no 25, 256803-1-256803-4 p.Article in journal (Refereed)
    Abstract [en]

    We solve the quantum Hall problem exactly in a limit and show that the ground states can be organized in a fractal pattern consistent with the Haldane-Halperin hierarchy, and with the global phase diagram. We present wave functions for a large family of states, including those of Laughlin and Jain and also for states recently observed by Pan et al., and show that they coincide with the exact ones in the solvable limit. We submit that they establish an adiabatic continuation of our exact results to the experimentally accessible regime, thus providing a unified approach to the hierarchy states.

  • 42.
    Berglund, Svante
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Engström, Magnus
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Holmgren, Sven-Olof
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Jon-And, Kerstin
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Lesser, Jonas
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Selldén, Björn
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Ramstedt, Magnus
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Silverstein, Sam
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Sjölin, Jörgen
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    The ATLAS Tile Calorimeter Digitizer2008In: Journal of Instrumentation, no 3, P01004- p.Article in journal (Refereed)
  • 43.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Antimatter and gamma-rays from dark matter annihilation2008In: J.Phys.Conf.Ser., 2008, 7- p.Conference paper (Other (popular science, discussion, etc.))
  • 44.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bringmann, Torsten
    Stockholm University, Faculty of Science, Department of Physics.
    Edsjö, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    New positron spectral features from supersymmetric dark matter: A way to explain the PAMELA data?2008In: Physical Review, Vol. 78, no 103520Article in journal (Other (popular science, discussion, etc.))
  • 45.
    Bergström, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fairbairn, Malcolm
    Stockholm University, Faculty of Science, Department of Physics.
    Pieri, Lidia
    X-ray Radiation from the Annihilation of Dark Matter at the Galactic Center2006In: Physical Review D, Vol. 74, no 123515Article in journal (Other (popular science, discussion, etc.))
  • 46.
    Bertoli, Gabriele
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Supersymmetry in Monojet Final States with the ATLAS Experiment2016Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The Large Hadron Collider is the most powerful particle accelerator built to date. The LHC is a proton–proton and heavy ion collider, in 2015 it operated at an un- precedented center of mass energy of sqrt(s) = 13 TeV. This thesis presents the results of the search for physics beyond the Standard Model of particle physics in a compressed supersymmetric squark–neutralino model. The present work uses an experimental sig- nature with a single high energetic jet and large missing transverse energy, so called monojet signature. The search is carried out using an integrated luminosity of 3.2 inverse femtobarn recorded by the ATLAS experiment in 2015. No significant excess compared to the Standard Model prediction has been observed thus a 95% CL limit has been set on the production of squark pairs with the subsequent decay ~q -> q + chi01 (q = u, d, c, s). Squark masses up to 608 GeV are excluded for m(~q) - m(chi01) = 5 GeV significantly improving earlier results.The Tile Calorimeter is the ATLAS hadronic calorimeter covering the central region of the detector. It is designed to measure hadrons, jets, tau particles and missing energy. In order to accurately be able to properly reconstruct these physical objects a careful description of the electronic noise is required. This thesis presents the work done in updating, monitoring and studying the noise calibration constants used in the processing of data and the identification of hadronic jets. These studies showed an unexpected variation over time of the cell noise and further investigation led to discover that the tile noise filter was not behaving as expected in some situations in approximately 5% of the detector cells.

  • 47.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Burgess, Christin
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Burgess, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hundertmark, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Thollander, Lars
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    The Search for Muon Neutrinos from Northern Hemisphere Gamma-Ray Bursts with AMANDA2008In: Astrophysical Journal, no 674, 357-370 p.Article in journal (Refereed)
  • 48.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Burgess, Thomas
    Stockholm University, Faculty of Science, Department of Physics.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics.
    Hundertmark, Stephan
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Wiedemann, Christin
    Stockholm University, Faculty of Science, Department of Physics.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Search for Point Sources of High Energy Neutrinos with Final Data from AMANDA-II2009In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 79, 062001- p.Article in journal (Refereed)
    Abstract [en]

    We present a search for point sources of high energy neutrinos using 3.8 yr of data recorded by AMANDA-II during 2000–2006. After reconstructing muon tracks and applying selection criteria designed to optimally retain neutrino-induced events originating in the northern sky, we arrive at a sample of 6595 candidate events, predominantly from atmospheric neutrinos with primary energy 100 GeV to 8 TeV. Our search of this sample reveals no indications of a neutrino point source. We place the most stringent limits to date on E-2 neutrino fluxes from points in the northern sky, with an average upper limit of E2Φνμτ≤5.2×10-11  TeV cm-2 s-1 on the sum of νμ and ντ fluxes, assumed equal, over the energy range from 1.9 TeV to 2.5 PeV.

  • 49.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Burgess, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hundertmark, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Wiedemann, Christin
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Solar Energetic Particle Spectrum on 13 December 2006 Determined by IceTop2008In: Astrophysical Journal Letters, no 689, L65-L68 p.Article in journal (Refereed)
  • 50.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Systemfysik.
    Burgess, Thomas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Hundertmark, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Thollander, Lars
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Wiedemann, Christin
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics. Elementarpartikelfysik.
    Search for Ultra High-Energy Neutrinos with AMANDA-II2008In: Astrophysical Journal, no 675, 1014-1024 p.Article in journal (Refereed)
1234567 1 - 50 of 435
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