The reaction

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• The reaction
• p d ? 3He p0 ?
• is interesting since
• we want to find out how baryon resonances are
  involved in the meson production
• we want to know more about the p0-? final state
  interaction
• the final state interaction of the p0-? system
  might give further information about the a0(980)
  resonance, which possibly has a qq-qq structure
  rather than a simple qq structure. The new higher
  maximum energy available at CELSIUS highly
  improves our chances to succeed in this point
  since the p0-? invariant mass approaches the mass
  of the a0(980) resonance

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• What will be done?
• the cross section of the reaction will be
  measured at several beam energies
• at one beam energy, the angular distributions and
  the invariant mass distributions of the final
  state particles will be studied in more detail
• we should also be able to measure the cross
  section of the reaction
• p d ? 3He ?
• for the case where ? decays into p0 ?, with the
  same trigger conditions as for the p0-?
  production
• 
  

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• What has been done?
• the reactions of interest and some background
  reactions have been simulated in order to get an
  idea of the detector acceptance and to find
  suitable trigger conditions
• a deuterium pellet target has been available
  since February 2004
• the maximum beam energy available at CELSIUS has
  been increased from 1360 MeV to 1450 MeV
• several shifts have been used for feasibility
  studies
• 
  

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Problems 1. The count rate in the FD is much
larger than expected from the luminosity
estimated from the cross section of the known
quasi free pp ? pp? ?Might be due to beam halo
interacting with the material in the beam pipe
?The possibility of improving the situation
using scrapers is under investigation 2. New
trigger schemes have to be developed. The
reaction of interest contains one 3He in the
final state. A good trigger that selects events
containing 3He is needed
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• 3He trigger developements
• We have been testing a requirement on high energy
  deposit in the Window Detector, that according to
  MC simulations would be highly selective.
• But the preliminary data analysis shows that it
  is very hard to get clean events corresponding to
  3He production.
• Some of the problem are that
• we expect one track only in the FD, but we get on
  average more than two
• a true 3He track giving a high energy deposit in
  the WD is expected to give a high energy deposit
  in the downstream detector layers, but offline
  analysis shows that most tracks dont!
• ?this points towards fake tracks that could be
  due to large angle scattering close to the WD

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• Possible trigger improvements
• a condition requiring high energy deposit in the
  Window Detector AND in some of the detector
  layers downstream
• the WD
• a condition requiring one and only one hit in
  the WD
• a condition requiring one and only one hit in
  the third layer of the JH
• Offline analysis shows that the conditions above
  give a clearer sample of 3He events.

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Analysis of data from March 2004, Tp1450
MeV, to test different trigger conditions
Obviously, the conditions mentioned give the
highest fraction of 3He events

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1.53 MA11

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• Where are we now?
• the CA80 experiment has not yet been able to run
  in a production mode but only for general
  developments
• the charge of shifts to this experiment is
  presently a matter of book-keeping between
  different experiments rather than a reflection of
  how much time that has been specifically devoted
  for the study of the
• p0-? production

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• Assuming
• a luminosity of 21030
• a detector acceptance of 20 (from simulations)
• trigger efficiency, detector efficiency, data
  acquisition efficiency, data analysing efficiency
  of 50 in total
• a p d ? 3He p0 ? cross section of 35 nb
• would give about 200 p d ? 3He p0 ? events per
  shift

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Beamtime request Considering the experimental
situation with further trigger improvement and
background reduction, we request 30 shifts to
continue the CA80 experiment