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Mesonic fusion - pion and eta meson production in light ion nuclear fusion reactions
Stockholm University, Faculty of Science, Department of Physics. (Kärnfysik)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis describes two experiments performed in the storage ring CELSIUS at The Svedberg Laboratory in Uppsala. In the first experiment the importance of three - nucleon clustering in the six - nucelon system was investigated. The total cross section for the production of the ground state and the 3.56 MeV second excited state of 6Li in the 3He(3He,6Li)π+ reaction has been measured at two beam energies, 261.1 and 262.5 MeV, corresponding to center - of - mass energies 1.2 and 1.9 MeV above the production threshold for the 3.56 MeV state. For the ground state the result was 347 ± 84 ± 42 and 92 ± 84 ± 11 nb respectively. The result for the 3.56 MeV state, 104 ± 23 ± 12 and 56 ± 35 ± 7 nb respectively, is compared to the result of a previous study where the 3.56 MeV state was populated in the d(4He,6Li)π0 reaction.

In the second experiment a clean sample of 5×105 eta mesons was prepared by means of the d(p,3He)η reaction. Eta production was tagged by the precise determination of the kinetic energy of the associated 3He ions. In the subsequent decay of eta mesons, channels with lepton - anti - lepton pairs were studied in the WASA detector. In a separate study properties of the WASA deuterium pellet target were investigated and in particular the effects on the beam of the beam - target interactions.

In both sets of experiments the fused nuclear system was detected by means of a zero - degree spectrometer with a semiconductor detector telescope. Choosing the detectors to match the rather different requirements, precise information regarding the identity and the momentum of the detected ions could be obtained in both cases.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 99 p.
Keyword [en]
pionic fusion, halo nuclei, cross sections, light mesons, eta-meson, WASA detector
National Category
Subatomic Physics
Research subject
Nuclear Physics
Identifiers
URN: urn:nbn:se:su:diva-39875ISBN: 978-91-7447-103-8 (print)OAI: oai:DiVA.org:su-39875DiVA: diva2:345172
Public defence
2010-10-01, FD5, AlbaNova universitetscentrum, Roslagstullbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2010-09-09 Created: 2010-06-02 Last updated: 2010-08-26Bibliographically approved
List of papers
1. Properties of the WASA pellet target and a stored intermediate-energy beam
Open this publication in new window or tab >>Properties of the WASA pellet target and a stored intermediate-energy beam
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2008 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2008
Keyword
Storage ring; Internal target; Pellet target; Beam–target interaction
National Category
Subatomic Physics
Research subject
Nuclear Physics
Identifiers
urn:nbn:se:su:diva-16701 (URN)doi:10.1016/j.nima.2007.12.040 (DOI)000255238600003 ()
Note
Totalt 8 författareAvailable from: 2008-12-22 Created: 2008-12-22 Last updated: 2010-08-26Bibliographically approved
2. Tagging of η mesons using the pd3Heη reaction near threshold
Open this publication in new window or tab >>Tagging of η mesons using the pd3Heη reaction near threshold
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2006 (English)In: Instruments and experimental techniques (New York), ISSN 0020-4412, E-ISSN 1608-3180, Vol. 49, no 4, 461-467 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2006
National Category
Subatomic Physics
Research subject
Nuclear Physics
Identifiers
urn:nbn:se:su:diva-12513 (URN)10.1134/S0020441206040038 (DOI)
Note
14 authorsAvailable from: 2008-01-15 Created: 2008-01-15 Last updated: 2010-08-26Bibliographically approved
3. Measurement of the η -> π+π-e+e- branching ratio
Open this publication in new window or tab >>Measurement of the η -> π+π-e+e- branching ratio
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2007 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 644, no 5-6, 299-303 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elesevier, 2007
Keyword
Eta meson decays; Dalitz decays
National Category
Subatomic Physics
Research subject
Nuclear Physics
Identifiers
urn:nbn:se:su:diva-42336 (URN)10.1016/j.physletb.2006.12.008 | (DOI)000243851000003 ()
Note
50 authorsAvailable from: 2010-08-25 Created: 2010-08-25 Last updated: 2017-12-12Bibliographically approved
4. Measurement of h meson decays into lepton-antilepton pairs
Open this publication in new window or tab >>Measurement of h meson decays into lepton-antilepton pairs
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2008 (English)In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 77, no 3, 32004-32008 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Physical Society, 2008
National Category
Subatomic Physics
Research subject
Nuclear Physics
Identifiers
urn:nbn:se:su:diva-16702 (URN)10.1103/PhysRevD.77.032004 (DOI)
Note
Totalt 52 författareAvailable from: 2008-12-22 Created: 2008-12-22 Last updated: 2010-08-26Bibliographically approved

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