In this presentation I will review the baseline design for Ce$^+$BAF and explain the R&D Plan for the next few years.
A photogun to generate high intensity, high polarization electron beam with unprecedented kC lifetime is being developed at JLab. The proposed Ce+BAF polarized positron source will require > 1 milliampere CW with > 90% polarization electron beam at 120 MeV. To be practical for a user program, a photogun operating at 1 milliampere should deliver ~ 2 kC high polarization beam for a month without...
I will give an update about the positron target effort at Jefferson Lab.
The very large power in electron beams needed to generate positrons and the accompanying enormous power densities preclude solid targets unless some complicated means of heat removal is implemented (e.g., cooled high-speed target rotation). A promising alternative is to use a windowless target and a liquid metal converter. Two liquid metals that have desirable properties for such a converter...
Simulations of beam particle interaction in the target have been used to estimate the background affecting the experiment, optimize the detector configuration, and determine the maximum acceptable luminosity. Lessons learned from CLAS12 background simulation studies will be discussed.
Deeply Virtual Compton Scattering (DVCS) is a privileged channel to study the structure of the nucleon as their experimental observables let us access information about Generalized Parton Distributions (GPDs). In general, the identification of DVCS events relies on the detection of only two final state particles as the kinematics of the third one can be reconstructed from conservation laws....
We investigate the corrections to the beam asymmetries in parity-violating electron scatterings arising from charge symmetry violation, strange quark, and charm quark distributions. Based on the parton distributions from the NNPDF Collaboration, these corrections could lead to $(1$-$2)\%$ uncertainties in the extraction of the weak couplings $g^{eq}_{AV}$ and $g^{eq}_{VA}$, and as large as...
The extraction of form factors, radii and related quantities have been
an important focus of research in the last decades. The research
intensity has increased with the proton radius puzzle about a decade ago, and more recently with results on the gravitational form factors. But the field is much wider, including also weak form factors, other radii and a multitude of particles beyond the...
One of the principal motivations for accelerating positrons in CEBAF is to perform direct measurements of positron-proton elastic scattering observables, toward a conclusive resolution of the long-standing discrepancy between extractions of the proton electromagnetic form factor ratio based on cross section measurements and double-polarization observables, especially polarization transfer....
In this talk I will discuss beam and target normal single-spin asymmetries in electron--proton elastic scattering. Our calculation of the imaginary part of two-photon exchange amplitudes considers resonance intermediate states of spin-parity 1/2± and 3/2± and mass W<1.8 GeV. The latest CLAS exclusive meson electroproduction data are used as input for the transition amplitudes from the proton...
Two-photon exchange gives rise to distinctive spin effects in electron/positron-nucleon scattering, which can be observed in inclusive or exclusive (elastic/inelastic) measurements. We report about recent progress in computing the transverse target single-spin asymmetry in ep scattering the resonance region, using systematic methods based on the 1/Nc expansion of QCD [1, 2]. We discuss the...
The connection of experimental data, notably in the DVCS channel, to generalized parton distributions (GPDs) faces a notoriously difficult deconvolution problem. I will present an impact study of the plausible impact of the positron beam on the extraction of Compton form factors, and discuss how this is a very useful data to consolidate the extraction of GPDs.
For the past 25 years, many JLab experiments have been dedicated to determining the Generalized Parton Distributions (GPDs), especially by measuring Deeply Virtual Compton Scattering (DVCS) observables. The GPDs describe the correlation between longitudinal momentum fraction and transverse position of partons in the nucleons. GPDs also give access to the Gravitational Form Factors (GFFs)...
We discuss opportunities with positron beams for the study of parton distribution functions of the nucleon in deep-inelastic scattering and related processes. Specific topics include the flavor separation of the unpolarized PDFs as well as the spin-dependent distributions.
Axial structure of the nucleon with positron capture at medium energies
A medium energy polarized positron beam would enable the extraction of the axial form factor $G_A(Q^2)$ of the nucleon and its four-momentum transfer square ($Q^2$) dependence, using the weak capture reaction in deuterium ($ \vec{e^+} + {^2H} \rightarrow 2p + \bar{\nu}_{e}$). A polarized positron beam with beam energies...
Semi-inclusive meson production is used to access transverse momentum dependent distributions (TMD) or partons in a nucleon. We investigate a role of two-photon exchange (TPE) for this process. Such calculations require a model of nucleon structure. At the first step, we perform separation of hard and soft photon exchange. Soft photon exchange is demonstrated to be model-independent due to a...
Inspired by the proton radius puzzle, the MUon Scattering Experiment (MUSE) at Paul Scherrer Institute (PSI) in Villigen, Switzerland, was introduced to provide new information by simultaneously measuring elastic scattering of electrons and muons, as well as positrons and antimuons from a liquid hydrogen target. MUSE aims to provide precise cross sections with extractions of the electric form...
