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 - ) Large kinematics coverage in Q 2, x, t Polarized beam, longitudinal & transverse polarized targets.

GPDs with Exclusive DVCS and ρ 0 /ρ + production at CLAS12 ep → epγ + X with E X = 0 ep → epρ 0 + X Exclusive Processes Need γ/π 0 identification for momentum ≤ 9 GeV/c

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

Exclusive Deeply Virtual Compton Scattering ep→e’p’γ GPD combinations accessible as azimuthal moments of the total cross section.  LU  ~ sin  {F 1 H( , t) +  (F 1 +F 2 ) H +kF 2 E } ~ Polarized beam, unpolarized target: Unpolarized beam, longitudinally polarized target:  UL  ~ sin  {F 1 H +  (F 1 +F 2 )( H +.. } ~ Unpolarized beam, transversely polarized target:  UT  ~ sin  {k(F 2 H – F 1 E ) + ….  }  = x B /(2-x B ) k = t/4M2 Kinematically suppressed at small t Kinematically suppressed

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

L = 1x10 35 T = 2000 hrs  Q 2 = 1 GeV 2  x = 0.05 E = 11 GeV Selected Kinematics  LU ~sin  Im{F 1 H +.  }d  e p ep  Projected results Exclusive DVCS with polarized beam

Exclusive DVCS on longitudinal 6GeV

e p ep  Longitudinally polarized target  ~sin  Im{F 1 H +  (F 1 +F 2 ) H... }d  ~ L = 2x10 35 cm -2 s -1 T = 1000 hrs  Q 2 = 1GeV 2  x = 0.05 Exclusive DVCS on longitudinal 12GeV CLAS Exclusive DVCS PRL97, (2006)

 Asymmetry highly sensitive to the u-quark contributions to proton spin. Transverse polarized target e p ep   ~ sin  Im{k 1 (F 2 H – F 1 E ) +…}d  Q 2 =2.2 GeV 2, x B = 0.25, -t = 0.5GeV 2 E = 11 GeV Sample kinematics A UTx Target polarization in scattering plane A UTy Target polarization perpedicular to scattering plane Exclusive DVCS on transverse target

Exclusive   production on transverse target 2  (Im(AB*))/  T          t/4m 2 ) - Re      UT  A ~ 2H u + H d B ~ 2E u + E d 00 K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 Q 2 =5 GeV 2 E u, E d needed for angular momentum sum rule. 00 A ~ H u - H d B ~ E u - E d ++

A UT  Exclusive   production on transverse target Strong sensitivity to d-quark contributions. A ~ H u - H d B ~ E u - E d ++ CLAS 5.7 GeV n 

CLAS12 - Acceptance for DVCS E = 11 GeV Q 2 > 2.5 GeV 2 ep ep  For small t, protons recoil at large polar angles. Forward Detector Central Detector

CLAS12 – Acceptance for DVCS ep epγ (π o ) E e = 11 GeV, x B = DVCS photons need detection for   > 2 o EC IEC γ

Page 15 Kinematics and Acceptance with CLAS + IC The much improved acceptance for photon detection, and the longer running time will allow us to extend the kinematics range to higher Q 2, and to map out the x B and t dependence in small bins DVCS studies require:  high Q 2  low t

Page 16 Target Spin Asymmetry:  Dependence A dedicated CLAS experiment with longitudinally polarized target will provide a statistically significant measurement of the kinematical dependences of the DVCS target SSA 6 GeV run with NH 3 longitudinally polarized target (CLAS + IC) 60 days of beam time  CLAS eg1 (preliminary) CLAS (eg1+IC) projected