Pi0 Polarizability Meeting Sep 13, 2019

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Meeting Information

Meeting Time And Location

10:00 am ET (JLab time)

CC F228


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Action Items

  1. Theory priority list and how to address them (Jose) Jose presented a list which was discussed by the group.

Tentative Agenda

  1. Announcements
  2. Action Items
  3. Theory Priorities (DRAFT) (Jose)
  4. Other business
  5. Next meeting


Attending: Alex (CMU); Mark, Jose, Beni, Elton (JLab); Aleks, Svetlana (MUN) ; Ilya, Rory (UMass).

  1. Announcements
  2. Action Items
    1. Elton has not received any response from emails to Dai. Lingyun Dai, Hunan University: Changsha, Hunan, CN (dailingyun@hnu.edu.cn)
  3. Theory Priorities (UPDATED) (Jose). Jose has updated his document from this morning. Some of his comments duplicate my notes below.
    1. Corrections due to virtuality. Jose mentioned that his recollection was that estimates of higher order corrections was 30%. There are both higher order ChiPT corrections in addition to corrections due to virtuality of the exchanged photon
      • Aleks suggested that one could calculate Compton scattering off a pi0 at one loop and evaluate the corrections due to virtuality in that case. It was agreed that this would be a good start
    2. Dispersive approach
      • Evaluating the impact of high mass data on the experiment may be important for the proposal.
      • Elton will provide a t distribution for the reaction.
      • Current group of theorists do not have great expertise in this area. One would need to learn about the approach and contact experts in this field.
      • We will reach out to experts in these areas (Pasquini, Moussallam, Dai and others) to see if they would be willing to support this effort.
    3. Move from gg*->pi0pi0 to gA->pi0pi0A.
      • Jose is almost finished with this calculation.
    4. Sensitivity of polarization to cross section
      • This depends on which meson exchanges (e.g. rho?) contribute to the reaction. One needs to identify the main exchanges.
      • Evaluate existing literature and create context for application to this proposal.
    5. Get control over all other contributions to the cross section, including nuclear corrections.
      • Take advantage of PRIMEX experience (single pi0) to see if one can extrapolate to this proposal (2 pi0s).
      • Engage Serguei to do some of the calculations for this case.
  4. Calculations of gp->pi0pi0 p (Aleks)
    • Aleks showed the diagrams contributing to gp -> pi0 pi0 p using ChiPT as a first step toward understanding the Primakoff reaction.
    • Elton: We might want to consider a large Z isoscaler source of virtual photons, which might be closer to the experimental situation.
    • Mark: Absolute cross section for reaction not as important as angular distribution for use in separating out nuclear coherent from the Primakoff signal.
    • Jose: Need to assess importance of various diagrams (see #4 above) in order to prioritize calculations.
  5. Other business
  6. Next meeting
    • Sep 27 at 10 am.