Plans for nucleon structure studies at PANDA

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Plans for nucleon structure studiesat PANDA

• The PANDA experiment _at_ FAIR
• Parton distributions
• GPDs
• Time-like form factors

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GSI upgrade
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Facility for Antiproton and Ion Research
SIS 100
SIS 300
SIS 18

• Broad range of high-intensity secondary beams
• Radioactive nuclei
• Antiprotons
• Cooler and storage rings
• Parallel operation

PANDA
HESR
Collector ring
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High Energy Storage Ring, HESR
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Target generator
Muon counters
EM and hadron calorimeters
solenoid
dipole
RICH

• Tracking of charged particles
• Identification of ?, e, µ, p, K, p, anti-p
• High rate capability
• Fast trigger scheme

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coil
barrel DIRC
Straws or TPC
MVD
mini drift chambers
EMC
electro magnetic calorimeter
disk DIRC
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top view
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PANDA physics programme
Charmonium spectroscopy
Exotics charmed hybrids heavy glueballs
Time-like form factors
Medium modificationsof charmed mesons
Drell-Yanprocesses
Hard exclusiveprocesses
CP-violation(D ? - sector)
Hypernuclei
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The nucleon spin puzzle
COMPASSRHIC
Gluon orbitalangular momentum(accessible
through GPDs, difficult)
Gluon polarisationpositive (HERMES)negative
(SMC)
HERMESCOMPASSPANDAJLab(upgrade)
Quark spin?? ? 0.25
Quark orbitalangular momentum(accessible
through GPDs)
Transversity
HERMES, COMPASSFNAL, (PANDA), PAX
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Parton distributions
Leading twist
directlyaccessible in Drell-Yan
Chirally odd
T-odd
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Drell-Yan processes

• Cross section depends on elementary process
• Measured as a function of polar angle ? and
  azimuthal angle ?
• Direct access to quark distribution functions(no
  fragmentation function involved)
• Complementary to DIS

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Drell-Yan processes and parton distributions

• Unpolarised DY ? Boer-Mulders DF h1- (PANDA _at_
  HESR)

• Single or double polarisation DY ?transversity
  h1(PAX _at_ HESR)

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Hard exclusive processes ? GPDs
Crossed channel (time-like)Wide Angle Compton
Scattering and DVCS

• Hard scalelarge s 10 GeV2 and t s, or
  large pT
• Soft part can be separated and parameterised by
  generalised distribution amplitudes
• Experimental problemlarge hadronic background
  (e.g. ?0?0)

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Count rate estimate A. Freund et al., PRL 90
(2003) 092001
Vector
Generalisedform factors

• Assumptions
• pbeam 5 GeV/c
• s 10 GeV2
• L 2x1032 cm-2s-1
• Results
• ? 2.5x10-10 fm2
• Rate 5x10-4 events/s gt 103
  events/month(probably underestimated by a factor
  3-4 according to CLEO data)

Axialvector
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Kinematics

• Photon CMSE? 15.5 0.5 GeV, ? 00 1800
• Wide angle scattering
• Large CM angles
• Large transverse momentapT few 100 MeV 2.7
  GeV
• Photon Lab E? 8 GeV, ? 200
• 4? calorimeter needed
• Background suppression
• Detectors with high-rate capability
• Charged particle veto in large acceptance
  spectrometer
• Check of exclusivity (momentum balance) through
  high-resolution calorimetry

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Experimental requirements

• Reject events with more than 2 primary final
  state particles
• Reject neutral mesons
• Tag one real photon with large pT
• 2nd photons momentum energy must add up to
  initial values

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First attempt at simulationsby G. Sebanut
Experiment appears feasible
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Time-like proton form factors
Crossed channel

• Goals
• To measure time-like FF from threshold up to
  high s q2 in one experiment(reduced systematic
  error)
• To compare with space-like FFs (pQCD at large s?)
• PANDA
• Wide kinematical range
• Large solid angle coverage
• Large statistics
• High-quality measurement of both GE and GM

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Timelines

• FAIR contract signed by participating countries
  by summer 2006
• PANDA technical design report 2007
• PANDA commissioning 2012 in Phase II of FAIR
  construction
• Data taking 2013