报告时间：2025年3月24日 下午16：00 (16:00, Mar. 24, 2025)

报告地点：物质科研楼B604会议室(Room B604, Material Science Building)

报告人:勾伯兴研究员

报告题目/Title: Accelerator-based new physics search in proton-electron scattering

摘要/Abstract: Within the Standard Model, transverse single spin asymmetries in electron elastic scatterings arise only from multi-photon exchanges. Experiments at MIT-Bates, MAMI, JLab, where transversely polarized electron beams scatter off both hydrogen and nuclei targets, show surprising deviations from theoretical calculations based on unitary and optical theorem. Comparing with the unitary calculation, one may attribute the discrepancy to heavier intermediate states in two-photon exchanges (TPE) which are not included in the calculation. On the other hand, it requires the virtual photon to have large energy to excite high-energy states, one would expect contributions due to these intermediate states are small. From this point of view, the discrepancy is puzzling.

Another possible origin of these discrepancies could be T-odd mechanisms beyond the Standard Model, such as a novel T-violating interaction or an unanticipated two-boson exchange involving one virtual photon and one unknown T-conserving boson. However, the uncertainties associated with intermediate states in TPE hamper us from investigating new physics. We propose to measure the transverse spin asymmetry in pe ⃗ scattering instead of e ⃗p scattering using an unpolarized proton beam and polarized electrons in a polarized hydrogen gas target, which is planned at the hadronic accelerator HIAF, currently under construction at IMP, CAS. In pe scatterings, the effective energy (or Q^2) is 2∼3 orders smaller than in ep scattering, only elastic intermediate state (i.e., proton) will be involved in two-photon exchanges. Therefore, theory based on unitarity can provide calculations with little theoretical uncertainties. In addition, the relativistic suppression on the asymmetries no longer exists if the electron is prepared as a target. As a result, the asymmetry will increase by 3 orders, compared with ep experiments with electron beams of 1∼2 GeV. Given the above advantages, the transversely polarized pe scattering could be an attractive approach to search for new physics.

报告人简介/Curriculum Vitae:

Boxing Gou is a scientist at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). He obtained his bachelor degree in engineering from the Northwestern Polytechnical University (NPU) in 2008, and pursued a doctoral degree of physics in the University of Chinese Academy of Sciences (UCAS) from 2009 to 2016. Boxing Gou performed experiments of nucleon-nucleon scattering for his PhD thesis with a polarized H/D gas target at the COoler SYnchrtron (COSY) at the Forschungszentrum Jülich (FZJ). Between 2017 and 2020, Boxing Gou conducted his postdoctoral research at the Helmholtz Institute Mainz (HIM), where he made significant contributions to the A4 experiment at the Mainz Microtron (MAMI) and to the P2 experiment at the Mainz Energy-Recovering Superconducting Accelerator (MESA). Currently, Boxing Gou is working on beam polarimeters for future hadron accelerators at IMP, CAS; meanwhile, he is conducting feasibility studies for spin-polarized experiments at High Intensity heavy-ion Accelerator Facility (HIAF).