Choose timezone
Your profile timezone:
Positron Working Group Workshop
→
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)
Description
LOCATION: Thomas Jefferson National Accelerator Facility
ROOM: F113
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
Contact
-
-
10:00 AM
→
12:30 PM
PWG - 1Convener: Dr Douglas Higinbotham (Jefferson Lab)
-
10:00 AM
Registration & Coffee 30m
-
10:30 AM
Workshop charge 20mSpeaker: Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab)
-
10:50 AM
The experiment that motivated Two-Photon effect studies 30m
A review of the past experiments which measured the ratio of the proton's electron to magnetic form factor at Jefferson Lab. An update will be given on the present experiment to measure the proton's electron to magnetic form factor up to Q2 = 12 GeV2
which will start running at the end of March 2025.Speaker: Mark Jones (Jefferson Lab) -
11:20 AM
Ce+BAF Working Group R&D plan 30m
The framework of the Ce+BAF Working Group 3-year R&D plan will be presented, with a special emphasis given to explaining some of the key technical challenges and thereby giving context to the accelerator presentations in this workshop.
Speaker: Joe Grames (JLab) -
11:50 AM
22 GeV accelearator plan and physics update 40m
Extending the energy reach of CEBAF up to 22 GeV within the existing tunnel is being explored. Proposed energy upgrade can be achieved by increasing the number of recirculations, while using the existing CEBAF SRF cavity system. Encouraged by recent success of the CBETA Test Accelerator, a proposal was formulated to raise CEBAF energy by replacing the highest-energy arcs with FFA arcs. The new pair of arcs configured with FFA (Fixed Field Alternating Gradient) lattice would support simultaneous transport of additional 6 passes with energies spanning a factor of two, using the non-scaling FFA principle implemented with Halbach-derived permanent magnets - a novel magnet technology that significantly saves energy and lowers operating costs. Further recirculation beyond 22 GeV is limited by large, 974 MeV per electron, energy loss and emittance dilution due to synchrotron radiation. Presented scheme requires replacement of the current 123 MeV injector with a 650 MeV 3-pass recirculating injector based on existing LERF infrastructure.
Speakers: Patrizia Rossi (JEFFERSON LAB), Alex Bogacz (Jefferson Lab)
-
10:00 AM
-
12:30 PM
→
2:00 PM
Lunch break 1h 30m
-
2:00 PM
→
5:30 PM
PWG - 2Convener: Joe Grames (JLab)
-
2:00 PM
Welcome 30mSpeakers: Kimberly Sawyer (JLab), David Dean (JLab)
- 2:30 PM
- 2:40 PM
- 2:50 PM
- 3:00 PM
- 3:10 PM
- 3:20 PM
-
3:30 PM
Tea break 30m
-
4:00 PM
Injection of e+ from LERF to experimental halls 30m
Jefferson Lab is planning an upgrade at the Continuous Electron Beam Accelerator Facility (CEBAF) to provide spin-polarized positrons to the experimental nuclear physics program. In this report, we present the beamline optics design which transports 123 MeV positrons beams created at the Low Energy Recirculator Facility (LERF) and injects them into CEBAF for acceleration to 12 GeV. The new injection design is constrained to fit into the existing racetrack-shaped CEBAF tunnel. Due to the large emittance of the positron beam, low-dispersion and low-beta function optics are desired and achieved in order to maximize the current transmission yet limited to the CEBAF acceptance. Furthermore, we report a preliminary multi-particle positron beam tracking to 12 GeV, providing spatial, momenta, and spin distribution to the nuclear physics experiments.
Speaker: Salim Ogur (Jefferson Lab)Jefferson Lab is planning an upgrade at the Continuous Electron Beam Accelerator Facility (CEBAF) to provide spin-polarized positrons to the experimental nuclear physics program. In this report, we present the beamline optics design which transports 123 MeV positrons beams created at the Low Energy Recirculator Facility (LERF) and injects them into CEBAF for acceleration to 12 GeV. The new injection design is constrained to fit into the existing racetrack-shaped CEBAF tunnel. Due to the large emittance of the positron beam, low-dispersion and low-beta function optics are desired and achieved in order to maximize the current transmission yet limited to the CEBAF acceptance. Furthermore, we report a preliminary multi-particle positron beam tracking to 12 GeV, providing spatial, momenta, and spin distribution to the nuclear physics experiments.
-
4:30 PM
Update on Ce+BAF injector baseline simulations 30m
Progress in the development of the positron injector concept for the Ce+BAF is presented. The results of start-to-end positron beam tracking simulations for two injector operating modes (low current high polarized beam and high current low polarized beam) are discussed. The efficiency of the positron capture system based on a normal conducting focusing solenoid downstream of the conversion target is compared with the efficiency of a superconducting solenoid.
Speaker: Andriy Ushakov (JLab) -
5:00 PM
The capturing cavity scheme for CW Ce+BAF positron source 30m
The Ce+BAF will be a CW positron source. In order to improve the efficiently capture the CW positron beam, a configuration of SRF cavities and solenoids beamline is explored. It is found that the SRF cavity could be used in CW positron capturing with high capturing efficiency.
Speaker: Shaoheng Wang (Jefferson Lab)
-
2:00 PM
-
10:00 AM
→
12:30 PM
-
-
8:00 AM
→
12:30 PM
PWG - 3Convener: Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab)
-
8:00 AM
Morning Coffee 30m
-
8:30 AM
LDRD for a high-current polarized-beam photogun 30m
The electron accelerator driving the Ce+BAF conversion target requires a spin-polarized photogun capable of delivering a CW beam current of at least 1 mA. As the high beam current limits the useful operating time of the gun between photocathode reactivations due to ion back-bombardment, it is critical to increase the charge lifetime. A Jefferson Lab LDRD project aims to calibrate the simulation models needed to predict photocathode lifetime as a function of electrostatic optics and drive laser parameters in order to design a gun providing at least 1000 C charge lifetime. A prototype gun demonstrating the validity of the scaling predictions will be built and tested at the Gun Test Stand. I will describe the background and progress of this project and give an outlook on the expected performance.
Speaker: Max Bruker (Jefferson Lab) -
9:00 AM
Solid target project 30mSpeaker: Silviu Covrig Dusa (Jefferson Lab)
- 9:30 AM
-
10:00 AM
Coffee break 30m
-
10:30 AM
Degraded beam study of CEBAF 30m
An electron beam degrader has been installed in the CEBAF injector in support of the positron capabilities of the machine, enabling machine acceptance measurements and testing of large emittance beam transport. This update provides the current state of the project, including proposed beam tests and preliminary results from simulations and previous beam studies.
Speaker: Victor Manuel Lizarraga-Rubio (Universidad de Guanajuato) -
11:00 AM
NTPE+ : measurement of the neutron two-photon exchange with quasi-elastic positron-neutron and electron-neutron scattering 30m
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) -
11:30 AM
Coulomb corrections in SIDIS 30m
Coulomb Corrections are largely unstudied and unconstrained in SIDIS, just as they are in DIS. Studies have shown that at at typical JLab kinematics, coulomb corrections calculated using the standard Improved Effective Momentum Approximation (IEMA) yield non-negligible corrections to measured cross sections. As the correction is directly proportional to the proton number of the target, any inaccuracies in these calculations would directly impact studies that compare nuclei. Of particular note is the upcoming SIDIS LT-separation measurement in Hall C. We propose to measure the coulomb corrections in SIDIS in Hall C using the CEBAF positron upgrade in order to directly access and constrain these effects.
Speaker: Tyler Hague (JLab) -
12:00 PM
Two-Photon Exchange in DIS and SIDIS 30m
Discrepancies between extractions of the proton form factor ratio when using Rosenbluth or Polarization transfer techniques has led to a strong interest in measuring the magnitude of two-photon exchange (TPE) effects using the planned CEBAF positron upgrade. TPE in inelastic scattering is comparatively less explored, but its study is well motivated. Two measurements of the imaginary part of the TPE contribution to inclusive deep inelastic scattering (DIS) disagree as to if the effect is observed at all. Predictions for TPE in semi-inclusive DIS (SIDIS) suggest that a very large (several percent) effect will be observed. A positron upgrade to CEBAF would provide a unique opportunity to directly measure the impact of TPE in DIS and SIDIS kinematics. We propose to measure this in Hall C over a carefully selected kinematic range in order to help constrain TPE calculations and to improve upcoming DIS and SIDIS LT-separation measurements.
Speaker: Michael Nycz (University of Virginia)
-
8:00 AM
-
12:30 PM
→
2:00 PM
Lunch break 1h 30m
-
2:00 PM
→
5:30 PM
PWG - 4Convener: Xiaochao Zheng (University of Virginia)
-
2:00 PM
Dispersive effects in unpolarized inclusive elastic electron/positron-nucleus scattering 30m
Dispersive corrections in electron scattering are still one of the fundamental quantities that lack precise experimental data and reliable theoretical predictions in the low to intermediate energy regime, including their A-dependencies. Their impacts on the nuclear charge and neutron distributions are investigated. Three avenues will be discussed to improve our understanding of these multi-photon exchange contribution to the scattering amplitude: a JLab/PAC53 proposal that follows the submission of LOI12-23-015, a data mining program on past Hall A/C experiments, and a complementary investigation study using rare isotopes with the MoNA Collaboration. While the former two use (un)polarized electron beams and can only provide qualitative information, a positron beam is required to accurately measure their magnitude.
Speaker: Paul Gueye (Facility for Rare Isotope Beams/Michigan State University) -
2:30 PM
Exploring lepton-charge asymmetries and parity-violation in large-pT SIDIS 30m
Lepton-charge asymmetries (LCAs) and parity-violation (PV) in DIS provide unique approaches to probe the proton structure and Standard Model parameters by considering the full neutral-current, one-boson exchange amplitude. While such effects have been extensively explored in the inclusive case, their role in SIDIS remains largely uncharted. In this talk, we present preliminary theoretical studies on observables that leverage these LCAs and PV in SIDIS, highlighting the advantages of using a positron beam and an upgrade to a 22 GeV beam at JLab to access them.
Speaker: Richard Whitehill (Old Dominion University / Jefferson Lab) -
3:00 PM
Photon source from positron annihilation 30mSpeaker: Andrei Afanasev (GWU)
-
3:30 PM
Tea break 30m
-
4:00 PM
Collaboration time 1h 30m
-
2:00 PM
-
6:30 PM
→
9:00 PM
Social event at the Chef's Market (11800 Merchants Walk, Newport News) 2h 30m
-
8:00 AM
→
12:30 PM
-
-
8:00 AM
→
1:00 PM
PWG - 5Convener: Eric Voutier (Université Paris-Saclay - CNRS/IN2P3/IJCLab)
-
8:00 AM
Morning Coffee 30m
-
8:30 AM
Spin asymmetries and their radiative corrections in low-energy elastic positron scattering 30m
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
Physics with the helicity-flip suppressed, transverse asymmetries in bhabha scattering 30m
Bhabha scattering will be one of the few e+e- reactions available to us at the JLab fixed target, polarized e+ facility. The rates in Hall C will be high enough to measure asymmetries with ppm level sensitivity, but not the ppb level sensitivity needed for credible parity violation measurements. What physics can we exploit from this? Because the Higgs-electron coupling to the electron is highly suppressed by the small electron mass, the s-channel in Bhabha scattering is dominated by the exchange of a gamma or Z. Their spin = 1 character enforces helicity conservation to an excellent approximation, leading to half a dozen transverse Bhabha asymmetries which are suppressed by the 1st or 2nd power of m_e/E_cm. I find that the s-channel exchange of spin = 0 can interfere with t-channel photon exchange to produce significant effects in a parity conserving asymmetry proportional to the helicity amplitude product F_LL*F_RR. Such a measurement has the potential to constrain the mass and couplings to electrons of BSM scalars, pseudo-scalars, and tensors, with no ambiguity as to whether on-shell decays of such BSM particles would be visible or invisible. I will also briefly discuss the singly helicity suppressed asymmetries A_LT and A_TU which have been suggested by Xin-Kai Wen et al as a way to constrain BSM dipole operators. All these Bhabha transverse asymmetries can be used to constrain BSM sources of helicity flip which are implied by the comparison of muon g-2 data and theory.
Speaker: David Mack (JLab) -
9:30 AM
Constraining two-photon exchange with electrons through the target-normal single spin asymmetry 30m
Accessing the contribution of hard two-photon exchange (TPE) in elastic scattering is one of the primary physics goals of the Jefferson Lab positron program. While asymmetries between positron- and electron-scattering provide direct access to TPE, there are other, pure electron observables that are sensitive to TPE, particularly normal single-spin asymmetries. In this talk, I present the possibility of measuring the target-normal single-spin asymmetry at CLAS12 using the transverse polarized target in development for Run Group H. This observable has never been measured for momentum transfers larger than 1 GeV^2, that is, the kinematics where TPE implicated in the discrepancy in the proton's electromagnetic form factors. Such a measurement would help improve our theoretical understanding of two photon exchange in advance of the JLab positron program. The measurement could also be repeated in the future using positron scattering, which could rule out more exotic mechanisms of time-reversal symmetry violation.
Speaker: Axel Schmidt (George Washington University) -
10:00 AM
Coffee break 30m
-
10:30 AM
A low-energy precision physics program at MESA: Hadrons and Nuclei as discovery tools. 30m
The Mainz Energy-recovering Superconducting Accelerator (MESA) is a cutting-edge facility designed to push the frontiers of particle, hadron, and nuclear physics. It will enable high-precision measurements, including the weak mixing angle at low energies, and contribute to beyond Standard Model physics. The two main MESA's experiments, P2 and MAGIX, will provide crucial insights into nucleon form factors, weak radii of nuclei, and dark matter, complementing other high-energy physics research and advancing our understanding of fundamental interactions.
Speaker: Concettina Sfienti (Johannes Gutenberg University Mainz) -
11:00 AM
Measurement of the weak pion-nucleon coupling constant from pion-photoproduction near threshold off the proton 30m
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) -
11:30 AM
Measurement of the proton Generalized Polarizabilities with positron and polarized electron beams 30m
The electromagnetic polarizabilities are fundamental properties of the proton that characterize its response to an external EM field. The generalization of the EM polarizabilities to non-zero four-momentum transfer opens up a powerful path to study the internal structure of the proton. They map out the spatial distribution of the polarization densities in the proton, provide access to key dynamical mechanisms that contribute to the electric and the magnetic polarizability effects, and allow to determine fundamental characteristics of the system, such as the electric and the magnetic polarizability radii. The Generalized Polarizabilities (GPs) have so far been accessed through measurements of the virtual Compton scattering reaction, utilizing an unpolarized electron beam that is scattered from a liquid-hydrogen target. In this talk, we will discuss an alternative experimental path to measure the proton GPs, that involves measurements with positron and polarized electron beams. Such experiments will add to the precision of the generalized polarizability measurements, but most importantly they will provide a much needed, unique and independent experimental cross-check to the world data, thus providing critical experimental input in order to address the critical theoretical challenges related to the GP measurements.
Speaker: Nikos Sparveris (Temple University) -
12:00 PM
Discussion on the Positron Technical Design Report 50mSpeaker: Dr Douglas Higinbotham (Jefferson Lab)
-
12:50 PM
Close-out 10m
-
8:00 AM
-
8:00 AM
→
1:00 PM
