The Charm of Excited Glue : Charmonium in e+e– and ppbar collisions

by Lundborg, Agnes

Abstract (Summary)
This thesis treats the mass range of charmonium states and excited gluonic fields in two experiments, BESII and PANDA, and outlines a phenomenological model that connects them.In BESII, e+e– form a charmonium initial state, which is utilised as a source for secondary particles. The analysed channels, ?´? ?K+K– and ?´? ??+?–, give access to intermediate scalar states such as the two glueball candidates: f0(1500) and f0(1710). The f0(1710) is indeed observed in decay into both ?+?– and K+K– and the f0(1500) is accepted as a necessary part of the ?+?– signal at the moderate 5% level. In addition, we observe the two tensor states f2(1270) (in both channels) and f2´(1525) (in K+K–), but the need for the f2´(1525) is not firmly established. The region around 2 GeV/c2 is fitted with an f4(2050) and an f0(2200) in ?+?–. This region is fairly flat in K+K– with a slight peak at the f0(2200). Branching ratios for all eight channels are given. A fit to the angular distribution of ?´? ? f2(1270) ? ? ?+?–gave two possible solutions for the relative importance of helicity projections zero, one and two.The future ppbar experiment PANDA is still in the development phase; important physics goals have been defined and we are now taking on the laborious task of constructing a detector that is able to fulfil them. A simulation investigation of a theoretically preferred JPC=1–+ charmonium hybrid (Hc) is presented: ppbar ? Hc?0/?, Hc ? ?c1 (?0?0)S–wave, ?c1 ? J/??0, with a final state of seven photons and a lepton pair. To detect this channel next to full coverage of CM phase space is needed and as little material as possible before the electromagnetic calorimeter. A second simulation study of ppbar ? ?c ? ?? at PANDA, suggests that the channel should be possible to detect with a signal-to-background ratio of 5±1 and a detection efficiency of at least 10%. By assuming a constant matrix element we obtain a relation between the decay width for ? ? ppbar+m, which has been measured at BES for several cases, and the cross section for ppbar charmonium production in association with the same light meson, m (at for example PANDA). Cross sections of ~300–3000 pb were predicted for J/? production and ~30 pb for ?' production. Isoscalars seem to be preferred to isovectors in J/? production, this might however be an artefact of simplifications within the model. A comparison with the only measured cross section, ppbar ? J/??0, suggests that the model is useful as a first estimate.
Bibliographical Information:


School:Uppsala universitet

School Location:Sweden

Source Type:Doctoral Dissertation

Keywords:Physics; hadron; charmonium; PANDA; antiproton; annihilations; spin-parity exotics; gluonic excitations; BES; hybrid; glueball; resonances; radiative decays; electromagnetic transitions; Fysik


Date of Publication:01/01/2007

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