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Joint INT/JLab/BNL Wokshop

Sunday, Oct. 29     Physics Building Room 1201

Hard exclusive processes with JLab 12 GeV

The aim of the discussions is to assess what measurements of hard exclusive processes at JLab 12 GeV can contribute to our knowledge of the nucleon GPDs, and to develop strategies for the analysis of the data. To organize the discussion, we broadly distinguish three regions, characterized by their own experimental and theoretical challenges and interest for nucleon structure

Experiment Theory Interest
I H(x, xi = 0, t) PDFs, formfactors Correlation x-t
(Regge, Lattice, etc)
2D quark imaging
II H(x, x = xi, t) Im(DVCS) from
spin asymmetries
Transition point behavior
QCD evolution
"Stopping" of fast quark
III H(x, xi, t) Re(DVCS) from cross section,
charge asymmetry;
meson production
General parametrizations 3D quark imaging
Sum rules Ju, Jd

The discussions in this workshop will focus on Regions II and III, where the GPDs are probed directly in hard exclusive processes (DVCS, meson production).

The presentations are intended to provide material for the discussions, and should be kept as concise as possible (10-15 min, unless otherwise agreed).

9:00 - 9:10 Welcome   [Ji]
9:10 - 9:30 Introduction and plan of discussion   [Weiss] [pdf]
9:30 - 12:00 GPD parametrizations   [Coordinators: Burkardt, Weiss]
  • Physical ideas and input
  • Incorporatig QCD evolution
  • Sensitivity of leading-twist observables
V. Guzey: "Dual" parametrization of GPDs and description of DVCS observables [pdf]
D. Müller: Towards a GPD fitting procedure [pdf]
A. Radyushkin: Double distributions and GPDs at x = xi
A. Schäfer: Long-term perspective of lattice calculations

13:30 - 16:00 Probing x = xi through DVCS spin observables   [Coordinators: Avakian, Weiss]
  • From data to leading-twist observables
  • Cross section vs. asymmetry measurements
  • Target mass and kinematic higher-twist corrections
  • Radiative corrections
M. Garcon: DVCS spin asymmetry with CLAS at 6 GeV
C. Munoz Camacho: DVCS cross section measurements at JLab [pdf]
E. Voutier: Quasi-free DVCS on the neutron in Hall A [ppt]
F. Ellinghaus: Ju,Jd from DVCS with transverse target polarization
V. Burkert: GPDs with exclusive DVCS and rho0 production at CLAS12 [ppt]
D. Müller: Target mass and kinematic higher-twist corrections in DVCS [pdf]

16:30 - 18:30 Probing x =/= xi in DVCS and meson production   [Coordinators: Guidal, Vanderhaeghen]
  • Observables accessing Re(DVCS)
  • Flavor separation of GPDs
  • Ratio observables in meson production
  • Experimental tests of leading vs. higher twist in meson production (L/T separation, t-slopes)
  • Theoretical approaches to higher twist in hard exclusive processes
F. Ellinghaus: DVCS charge asymmetries
A. Sandacz: Exclusive processes at COMPASS - present and future [pdf]
M. Guidal: Vector meson production and GPDs
C. Munoz Camacho: Recent pi0 results from Hall A
M. Strikman: GPD studies in hard exclusive meson production [pdf]
19.00 - 20.00 Open discussion of future plans
after 20:00 Informal dinner at local restaurant

Monday, Oct. 30     Kim Engineering Building Room 1105

Hard exclusive processes with a future ep collider

9:00 - 11:30 The x, Q²-landscape for exclusive measurements   [Coordinators: Deshpande, Ent, Strikman]
M. Strikman:   Hard exclusive processes with a future ep/eA collider [pdf]
V. Guzey:   Feasibility study for nuclear DVCS in collider kinematics [pdf]
F. Ellinghaus:   First experimental results on DVCS from nuclei
A. Levy: Exclusive measurements at HERA
13:00 - 16:00 GPD studies with future facilities   [Coordinators: Deshpande, Ent, Strikman]
H. Abramowicz: Lessons for a future ep collider
Ch. Montag: Interaction region constraints for ep/eA colliders [pdf]
A. Sandacz:   Hard exclusive processes at EIC - experimental aspects [pdf]
R. Milner: Access to quark and gluon GPDs with an ep collider
16:30 - 18:30 Open discussion of future plans (White paper)