Pi0 Polarizability Meeting Nov 15, 2019

Meeting Information

Meeting Time And Location

10:00 am ET (JLab time)

CC F228

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Action Items

1. Event generator. Equation for g A -> g pi0 pi0
2. Primakoff signal rate for He/Be targets (Elton)
3. Contact theorists:
   • Lingyun Dai, Hunan University: Changsha, Hunan, CN (dailingyun@hnu.edu.cn)
   • Serguei Gevorkyan
   • Barbara Pasquini (Rory)

Tentative Agenda

1. Announcements
2. Action Items
   • Rory contacted Barbara. She is very busy at the moment, but promised to take a look at our LOI and let us know how she might be able to support our effort.
3. Theory update
   • Notes Jose Nov 15
   • Jose walked us through the updated version of his notes.
   • Jose has written the cross section in the lab frame and in the forward limit.
   • For two real photons in gg->pi0pi0, there are 2 hadronic tensors, corresponding to two form factors (A and B).
   • For one real and one Coulomb photon gg_C->pi0pi0, there are 3 hadronic tensors, corresponding to three form factors (A, B and C). Previous calculations have ignored the virtuality of the Coulomb photon.
   • In the low-energy (unpolarized) limit, the polarizabilities are alpha ~ (A+12 m_pi B), beta ~ -A. The interpretation of C is still needed.
   • Jose will continue developing his calculations toward a cross section for polarized photons on a heavy target.
4. Rates on Be (Elton)
   • Assume 5% target for both Pb and Be. [Note: Ilya checked that the Be target in Gluex is 0.7" (1.78 cm) thick and 1" (2.54 cm) in diameter]
   • Calculations with some parameterizations for Pb and Be, the expected signal rates on Be are about 90% of those expected on a Pb target.
5. Other business
6. Next meeting

Minutes

Attending: