Bulletin of the American Physical Society
Fall 2022 Meeting of the APS Division of Nuclear Physics
Volume 67, Number 17
Thursday–Sunday, October 27–30, 2022; Time Zone: Central Daylight Time, USA; New Orleans, Louisiana
Session EA: Probing Nuclear Geometry with Photons from JLab to RHIC and LHC |
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Chair: Janet Seger, Creighton University Room: Hyatt Regency Hotel Celestin D |
Friday, October 28, 2022 10:30AM - 11:06AM |
EA.00001: Generalized Electromagnetic Polarizabilities of the Proton with VCS at JLab Invited Speaker: Nikos Sparveris A fundamental property of the proton involves the system's response to an external electromagnetic (EM) field. It is characterized by the EM polarizabilities that describe how easily the charge and magnetization distributions inside the system are distorted by the EM field and the generalized polarizabilities that map out the resulting deformation of the densities in a proton subject to an EM field. They reveal unique information regarding the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents together. Of particular interest is a puzzle in the proton's electric generalized polarizability that remains unresolved for two decades. This talk will offer an overview on this topic, the discussion of new results from JLab and of future prospects. |
Friday, October 28, 2022 11:06AM - 11:42AM |
EA.00002: Discovery of the Breit-Wheeler Process and its Application to Nuclear Charge and Mass Radii Measurements Invited Speaker: Daniel Brandenburg Only a handful of fundamental interactions between light and matter are allowed by the theory of quantum electrodynamics, almost all of which have been observed in the 80+ years since their prediction. Among the tree level interactions, only the Breit-Wheeler process, the simplest mechanism for converting 'light quanta' into matter and antimatter, eluded observation despite being hotly pursued. The key challenge has been obtaining a photon source with sufficiently high intensity and energy, such that two photons will collide with a center-of-mass energy of at least twice the electron mass. |
Friday, October 28, 2022 11:42AM - 12:18PM |
EA.00003: Impact Parameter Dependence of Photon-Induced Processes in Heavy-Ion Collisions Invited Speaker: Shuai Yang The Lorentz boosted electromagnetic fields shrouding relativistic heavy ions can be treated as a flux of linearly polarized quasi-real photons. Therefore, ions can interact when their impact parameter is greater than twice the nuclear radius, the so-called ultraperipheral collisions (UPCs), via photon-photon process. This photon-photon process has also been observed in hadronic heavy-ion collisions. The intriguing thing is that the mean transverse momentum (pT) of lepton pairs from photon-photon scatterings in hadronic collisions is found to be larger than that from UPCs. This phenomenon sparked an intense discussion in the field that whether the observed broadening is caused by final-state electromagnetic modifications of lepton pairs in a Quark Gluon Plasma (QGP) medium or pT hardening of initial-state photons as the impact parameter decreases toward central hadronic collisions. |
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