Discussion 07-15-24

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Meeting Location

The 22 GeV Open Discussions will be held here:

• Date/Time: Monday, July 15 at 12:30 PM Jefferson Lab Local Time
• Physical Location: CEBAF Center F224/5
• Virtual Location: Zoom Meeting Number 161 111 8017 (The password is the two-digit number that appears before "GeV" in the first sentence of this section.

Agenda

• Double Deeply Virtual Compton Scattering (DDVCS) at 22 GeV (Stepan Stepanyan)

Comments and Questions

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Minutes/Notes (D.S. Carman)

Local participants at JLab: 15; Remote participants: 44

• Goal – Measure Double DVCS (DDVCS) with a 22 GeV electron beam in Hall B with CLAS12 outfitted as a forward muon detector (μCLAS12) with luminosity > 10³⁷ cm^-2s^-1

• Presentation points:
  • The goal of a study of DDVCS is to explore nucleon tomography using a GPD framework to study the full kinematic phase space vs. x, ξ, t over the momentum transfer variables Q² (production side) and Q’² (decay side) to access the space-like and time-like regions.
  • DDVCS studies can shed light on issues with GPD extractions using DVCS and TCS processes.
  • Electrons at 22 GeV are necessary to access the space-like regime for time-like virtualities above the meson resonance region M_l+l- > 2 GeV.
  • Experimental considerations/design for 22 GeV are being considered during planning for initial 11 GeV μCLAS12 experiment.

• Questions from discussion:
  • How to access GPDs from measurements of DDVCS? The present scheme is first to extract Compton Form Factors from the data and then to use models of GPDs (so-called GPD functionals) to access the GPDs. This approach is tricky, non-unique, and model dependent. This whole process should be studied to develop a framework and to explore sensitivity of GPD extractions to various (reasonable) assumptions.
  • The experiment sensitivity will need proper simulations to project expected results in a reasonable experimental program. This sensitivity will necessarily include not just experiment statistics/binning but expected sensitivity to GPDs.
  • A question that applies to the DDVCS process (as much as for DVCS, TCS, …) is the applicability of the handbag diagram. It will be important to detail the possible background contributions and how they can be minimized/studied with various kinematic cuts.
  • A key aspect of the increase in the beam energy to 22 GeV is the ability to remove the vector meson contributions with a cut on the di-lepton mass above 2 GeV. However, including lower masses may be necessary to increase statistics with suitable cuts to remove the di-lepton resonances.
  • It would be good to more carefully layout the common and complementary aspects of the DDVCS program with CLAS12 at 22 GeV and with SOLID in Hall A at 22 GeV.