Pi0 Polarizability Meeting Aug 16, 2019

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Meeting Information

Meeting Time And Location

10:00 am ET (JLab time)

CC F224-225

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Tentative Agenda

  1. Announcements
  2. PAC 47
    1. TAC Physics Comments
      • One-pion exchange contribution (C-parity conservation?)
      • Eliminating contributions from iso-scalar resonances (experiment)
      • Sensitivity of cross sections to polarizability (theory)
      • Corrections due to photon virtuality (theory)
    2. email from Elton and Mark to PAC Reviewer Steve Dytman. Homework to prepare for a proposal (Questions not answered by the LOI):
      • So far we have only qualitatively investigated backgrounds, but do not find any particular reactions that have not been considered for pi0 and pi+pi- Primakoff reactions. Detailed studies needed.
      • Determine how backgrounds will affect the determination of the pi0pi0 Primakoff cross section.
      • Evaluate sensitivity to run time. Need to justify requested beam time.
      • Develop the case for measuring pi0pi0 production at threshold aside from the determination of the polarizability.
    3. PAC47 Report
  3. Other business
  4. Next meeting

Minutes

Attending: Elton, David, Mark, Rory

  1. Announcements
  2. PAC 47
  3. TAC Physics Comments
    1. One-pion exchange contribution (C-parity conservation?)
      • Rory: this is the chiral anomaly term gpi0->pi0pi0. May not be large but is calculable. Jose can probably do the calculation. It falls into the category of coherent backgrounds (relatively large -t). Interesting in its own right and closely related to the pi0 lifetime.
    2. Eliminating contributions from iso-scalar resonances (experiment)
      • Rory: The gg -> pi0pi0 cross section includes ChiPT calculation + Born terms + resonance terms. These latter diagrams need to be assessed outside of ChiPT. This reaction is a "laboratory for ChiPT."
      • We talked about reaching out to other theorists, in particular Dai (from Dai and Pennington) and Barbara Pasquini. Elton will try to contact Dai before the next meeting.
    3. Sensitivity of cross sections to polarizability (theory)
      • This is a task that needs guidance from theory to help us extract polarization physics from the measured cross section.
    4. Corrections due to photon virtuality (theory)
      • Rory: Does inserting the nucleon form factors take care of this?
      • Elton: Jose has been concerned with this issue and he can give us an update at the next meeting.
      • Mark: According to Jose, Moussallam's calculations are for virtual photons, so we might be able to use his work/framework.
  4. email from Elton and Mark to PAC Reviewer Steve Dytman. Homework to prepare for a proposal (Questions not answered by the LOI):
    1. So far we have only qualitatively investigated backgrounds, but do not find any particular reactions that have not been considered for pi0 and pi+pi- Primakoff reactions. Detailed studies needed.
      • Mark: There are two steps: 1) from the measured gPb->pi0pi0 cross section determine g g -> pi0 pi0. This is our work as experimentalists. 2) From the g g -> pi0 pi0 cross section extract physics of interest (e.g. polarizability).
    2. Determine how backgrounds will affect the determination of the pi0pi0 Primakoff cross section.
    3. Evaluate sensitivity to run time. Need to justify requested beam time.
    4. Develop the case for measuring pi0pi0 production at threshold aside from the determination of the polarizability.
  5. PAC47 Report
    • Rory: At this point, the simulation is in good shape (demonstrated in the LOI is resolution, acceptance, etc). We need theoretical interpretation and address background issues.
  6. Other business
  7. Next meeting
    • We will plan for our next meeting in two weeks (Aug 30), but it should make sure that Jose, Svetlana and Aleks can participate.
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