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Experimental requirements for GPD measurements at JLab energies.

Experimental requirements for GPD measurements at JLab energies. Detector that ensures exclusivity of process, measurement of complete final state Measure single γ ( DVCS) & π 0 simultaneously up to 9 GeV/c Vector mesons & pseudoscalar mesons Double DVCS (e + e - , µ + µ - )

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Experimental requirements for GPD measurements at JLab energies.

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  1. Experimental requirements for GPD measurements at JLab energies. • Detector that ensures exclusivity of process, measurement of complete final state • Measure single γ (DVCS) & π0 simultaneously up to 9 GeV/c • Vector mesons & pseudoscalar mesons • Double DVCS (e+e-, µ+µ-) • Large kinematics coverage in Q2, x, t • Polarized beam, longitudinal & transverse polarized targets.

  2. GPDs with ExclusiveDVCS and ρ0/ρ+ productionat CLAS12 Exclusive Processes ep → epγ+ X with EX = 0 ep → epρ0+ X Need γ/π0 identification for momentum ≤ 9 GeV/c

  3. CLAS12 – Complete event reconstruction Forward Calorimeter Preshower Calorimeter Forward Cerenkov (LTCC) Forward Time-of-Flight Detectors Forward Drift Chambers Superconducting Torus Magnet New TOF Layer Inner Cerenkov (HTCC) Central Detector Optimized for unpolarized & polarized target experiments. Beamline Instrumentation Inner Calorimeter * Reused detectors from CLAS

  4. Exclusive Deeply Virtual Compton Scattering ep→e’p’γ Polarized beam, unpolarized target: ~ DsLU~ sinf{F1H( x,x,t)+ x(F1+F2)H+kF2E} Kinematically suppressed at small t Unpolarized beam, longitudinally polarized target: ~ x = xB/(2-xB ) k = t/4M2 DsUL~ sinf{F1H+x(F1+F2)(H+.. } Kinematically suppressed Unpolarized beam, transversely polarized target: DsUT~ sinf{k(F2H – F1E) + …..} Kinematically suppressed GPD combinations accessible as azimuthal moments of the total cross section.

  5. H1, ZEUS Deeply Virtual Exclusive Processes - Kinematics Coverage of the 12 GeV Upgrade H1, ZEUS 27 GeV 11 GeV 11 GeV 200 GeV JLab Upgrade JLab @ 12 GeV COMPASS W = 2 GeV HERMES Study of high xB domain requires high luminosity 0.7

  6. e p epg L = 1x1035 T = 2000 hrs DQ2 = 1 GeV2 Dx = 0.05 Exclusive DVCS with polarized beam Projected results E = 11 GeV DsLU~sinfIm{F1H+..}df Selected Kinematics

  7. ExclusiveDVCSonlongitudinal target @ 6GeV

  8. L = 2x1035 cm-2s-1 T = 1000 hrs DQ2 = 1GeV2 Dx = 0.05 e p epg CLAS Exclusive DVCS PRL97, 072002 (2006) ExclusiveDVCSonlongitudinal target @ 12GeV Longitudinally polarized target ~ Ds~sinfIm{F1H+x(F1+F2)H...}df

  9. Sample kinematics e p epg E = 11 GeV Q2=2.2 GeV2, xB = 0.25, -t = 0.5GeV2 • Asymmetry highly sensitive to the u-quark contributions to proton spin. ExclusiveDVCSontransverse target Transverse polarized target Ds ~ sinfIm{k1(F2H– F1E) +…}df AUTx Target polarization in scattering plane AUTy Target polarization perpedicular to scattering plane

  10. Q2=5 GeV2 Exclusiver0productionon transverse target K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 2D (Im(AB*))/p T AUT = - |A|2(1-x2) - |B|2(x2+t/4m2) - Re(AB*)2x2 A ~ 2Hu + Hd r0 B ~ 2Eu + Ed A~ Hu - Hd B ~ Eu - Ed r+ r0 Eu, Ed needed for angular momentum sum rule.

  11. CLAS 5.7 GeV r+ n Exclusive r+production on transverse target Strong sensitivity to d-quark contributions. A~ Hu - Hd B ~ Eu - Ed AUT r+

  12. For small t, protons recoil at large polar angles. CLAS12-Acceptance for DVCS E = 11 GeV ep epg Q2 > 2.5 GeV2 Central Detector Forward Detector

  13. CLAS12 – Acceptance for DVCS Ee = 11 GeV, xB = 0.325-0.375 EC ep epγ (πo) IEC DVCS photons need detection for Qg > 2o γ EC EC IEC IEC

  14. Kinematics and Acceptance with CLAS + IC • DVCS studies require: • high Q2 • low t The much improved acceptance for photon detection, and the longer running time will allow us to extend the kinematics range to higher Q2, and to map out the xB and t dependence in small bins

  15. Target Spin Asymmetry: f Dependence 6 GeV run with NH3 longitudinally polarized target (CLAS + IC) 60 days of beam time • CLAS eg1 (preliminary) • CLAS (eg1+IC) projected A dedicated CLAS experiment with longitudinally polarized target will provide a statistically significant measurement of the kinematical dependences of the DVCS target SSA

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