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.
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.
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...
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...
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.
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
