Positron Working Group Workshop

Mar 24, 2025, 10:00 AM → Mar 26, 2025, 5:00 PM US/Eastern

Axel Schmidt (George Washington University), Douglas Higinbotham (Jefferson Lab), Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab), Joe Grames (JLab), Xiaochao Zheng (University of Virginia)

LOCATION:  Thomas Jefferson National Accelerator Facility

ROOM:  L102

REGISTRATION:  https://misportal.jlab.org/ul/conferences/generic_conference/registration.cfm?conference_id=Positron325

ZOOM:  https://jlab-org.zoomgov.com/j/1615221081?pwd=BrsIwLjURTtt02ozJvQD1LIn4k0OsN.1 

 

Monday, March 24

10:00 AM → 12:30 PM PWG - 1

Convener: Dr Douglas Higinbotham (Jefferson Lab)

10:00 AM Registration & Coffee

10:30 AM Workshop charge

Speaker: Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab)

10:50 AM TBD

11:20 AM Ce+BAF Working Group R&D plan

Speaker: Joe Grames (JLab)

11:50 AM TBD

12:10 PM TBD

12:30 PM → 2:00 PM Lunch break

2:00 PM → 5:30 PM PWG - 2

Convener: Joe Grames (JLab)

2:00 PM Injection of e+ from LERF to experimental halls

Speaker: Salim Ogur (Dr)

2:30 PM Update on Ce+BAF injector bqseline simulations

Speaker: Andriy Ushakov (JLab)

3:00 PM NCRF/SCRF e+ capture

3:30 PM Tea break

4:00 PM NTPE+ : measurement of the neutron two-photon exchange with quasi-elastic positron-neutron and electron neutron scattering

The first measurements of elastic electron nucleon scattering with polarization transfer, allowing to separate the electric and magnetic nucleon form factors, showed a significant discrepancy with Rosenbluth measurement of the cross section of the same process. The two-photon exchange, suspected to be the cause of this observation, got a major focus since then. The two-photon exchange is expected to depend on the charge of the lepton, meaning that the ratio of positron-nucleon to electron-nucleon measurements should clarify the role of the two photon exchange in the aforementioned discrepancy.
We propose measurements of the quasi-elastic positron-neutron and electron-neutron at Q2 = 3.0 (GeV/c)2, 4.5 (GeV/c)2 and 6 (GeV/c)^2, combined with Rosenbluth measurements at these kinematics. These measurements purport to complete and extend the measurement of the two-photon exchange in electron-neutron scattering submitted to and approved by PAC48 in 2020, and recorded in 2022 (experiment E12-20-010 currently under analysis). It would be performed with the Super BigBite Spectrometer installed in Hall C and will measure simultaneously positron-proton and
positron-neutron scattering off deuterium.
I will present the motivations and details of the proposed measurement, and provide a few aspects of the ongoing analysis of experiment E12-20-010 relevant to this new measurement.

Speaker: Eric Fuchey (College of William and Mary)

4:30 PM Two-Photon Exchange in DIS and SIDIS

5:00 PM Coulomb corrections in SIDS

Tuesday, March 25

8:00 AM → 12:40 PM PWG - 3

Convener: Axel Schmidt (George Washington University)

8:00 AM Mornig Coffee

8:30 AM TBD

9:00 AM TBD

9:30 AM TBD

10:00 AM Coffee break

10:30 AM High-current polarized beam photogun

Speaker: Max Bruker (Jefferson Lab)

10:55 AM Solid target project

Speaker: Silviu Covrig Dusa (Jefferson Lab)

11:20 AM Liquid target project

Speaker: Vaclav Kostroun (Xelera Research)

11:45 AM Degraded beam study of CEBAF

Speaker: Victor Manuel Lizarraga-Rubio (Universidad de Guanajuato)

12:40 PM → 2:00 PM Lunch break

2:00 PM → 5:30 PM PWG - 4

Convener: Xiaochao Zheng (University of Virginia)

2:00 PM TBD

Speaker: Axel Schmidt (George Washington University)

2:30 PM TBC

Speaker: Ciprian Gal (Jefferson Lab)

3:00 PM TBC

Speaker: Richard Whitehill (Old Dominion University / Jefferson Lab)

3:30 PM Tea break

4:00 PM An energy upgrade for Hall D

Speaker: Andrei Afanasev (GWU)

4:30 PM TBD

5:00 PM TBD

7:00 PM → 9:30 PM Social event at the Chef's Market (11800 Merchants Walk, Newport News)

Wednesday, March 26

8:00 AM → 12:30 PM PWG - 5

Convener: Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab)

8:00 AM Morning Coffee

8:30 AM Spin symmetries and their radiative corrections in low-energy elastic positron scattering

The beam-normal spin asymmetry from polarized positron scattering is investigated in the energy regime 1−150 MeV by means of the phase-shift analysis. The nonperturbative consideration of QED effects leads to spin-asymmetry changes of a few percent irrespective of the target nucleus. Corrections from low-lying transient nuclear excitations depend strongly on the collision geometry and the target species. Comparison is made with the respective results from polarized electron scattering. Two spin-zero nuclei, 12C
and 208Pb, are taken as examples.

Speaker: Doris Jakubaßa-Amundsen (Universty of Munich)

9:00 AM TBD

Speaker: David Mack (JLab)

9:30 AM TBD

10:00 AM Coffee break

10:30 AM Measurement of the weak pion-nucleon coupling constant from pion-photoproduction near threshold off the proton

The longest-range weak pion-nucleon coupling constant, h_π^1, is important for nuclear parity violation. Prospects of a new measurement of h_π^1 in a theoretically clean process are presented. A measurement of the parity-violating asymmetry in pion photoproduction off the proton is related to h_π^1 in a low-energy theorem of the photon polarization asymmetry at threshold in the chiral limit. A reliable measurement of h_π^1 provides a crucial test of the meson-exchange picture of the weak N-N interaction. Such a test of the meson-exchange picture will shed light on low energy QCD.

Speaker: Riad Suleiman (Jefferson Lab)

11:00 AM TBD

11:30 AM TBD

12:30 PM → 2:00 PM Lunch break

2:00 PM → 5:00 PM PWG - 6

2:00 PM TBD

2:30 PM Discussion on the Technical Design Report

Speaker: Dr Douglas Higinbotham (Jefferson Lab)

3:30 PM Close-out