The beam-helicity asymmetry in associated electroproduction of real photons, eparrow righteγpiN , in the Delta(1232)-resonance region is measured using the longitudinally polarized Hera positron beam ...and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, eparrow righteγpi^sup 0^ p and eparrow righteγpi^sup +^ n, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.
The Electron-Ion Collider (EIC), a state-of-the-art facility for studying the strong force, is expected to begin commissioning its first experiments in 2028. This is an opportune time for artificial ...intelligence (AI) to be included from the start at this facility and in all phases that lead up to the experiments. The second annual workshop organized by the AI4EIC working group, which recently took place, centered on exploring all current and prospective application areas of AI for the EIC. This workshop is not only beneficial for the EIC, but also provides valuable insights for the newly established ePIC collaboration at EIC. This paper summarizes the different activities and R&D projects covered across the sessions of the workshop and provides an overview of the goals, approaches and strategies regarding AI/ML in the EIC community, as well as cutting-edge techniques currently studied in other experiments.
The search for a dark photon holds considerable interest in the physics community. Such a force carrier would begin to illuminate the dark sector. Many experiments have searched for such a particle, ...but so far it has proven elusive. In recent years the concept of a low mass dark photon has gained popularity in the physics community. Of particular recent interest is the \(^8\)Be and \(^4\)He anomaly, which could be explained by a new fifth force carrier with a mass of 17 MeV/\(c^2\). The proposed DarkLight experiment would search for this potential low mass force carrier at ARIEL in the 10-20 MeV e\(^+\)e\(^-\) invariant mass range. This proceeding will focus on the experimental design and physics case of the DarkLight experiment.
We report the first measurement of the parity-violating elastic electron scattering asymmetry on 27Al. The 27Al elastic asymmetry is A_PV = 2.16 +- 0.11 (stat) +- 0.16 (syst) ppm, and was measured at ...<Q^2> =0.02357 +- 0.0001 GeV^2, = 7.61 +- 0.02 degrees, and = 1.157 GeV with the Qweak apparatus at Jefferson Lab. Predictions using a simple Born approximation as well as more sophisticated distorted-wave calculations are in good agreement with this result. From this asymmetry the 27Al neutron radius R_n = 2.89 +- 0.12 fm was determined using a many-models correlation technique. The corresponding neutron skin thickness R_n-R_p = -0.04 +- 0.12 fm is small, as expected for a light nucleus with a neutron excess of only 1. This result thus serves as a successful benchmark for electroweak determinations of neutron radii on heavier nuclei. A tree-level approach was used to extract the 27Al weak radius R_w = 3.00 +- 0.15 fm, and the weak skin thickness R_wk - R_ch = -0.04 +- 0.15 fm. The weak form factor at this Q^2 is F_wk = 0.39 +- 0.04.
Upgrading the SuperKEKB electron-positron collider with polarized electron beams opens a new program of precision physics at a center-of-mass energy of 10.58 GeV. This white paper describes the ...physics potential of this `Chiral Belle' program. It includes projections for precision measurements of \(\sin^2\theta_W\) that can be obtained from independent left-right asymmetry measurements of \(e^+e^-\) transitions to pairs of electrons, muons, taus, charm and b-quarks. The \(\sin^2\theta_W\) precision obtainable at SuperKEKB will match that of the LEP/SLC world average, but at the centre-of-mass energy of 10.58 GeV. Measurements of the couplings for muons, charm, and \(b\)-quarks will be substantially improved and the existing \(3\sigma\) discrepancy between the SLC \(A_{LR}\) and LEP \(A_{FB}^b\) measurements will be addressed. Precision measurements of neutral current universality will be more than an order of magnitude more precise than currently available. As the energy scale is well away from the \(Z^0\)-pole, the precision measurements will have sensitivity to the presence of a parity-violating dark sector gauge boson, \(Z_{\rm dark}\). The program also enables the measurement of the anomalous magnetic moment \(g-2\) form factor of the \(\tau\) to be made at an unprecedented level of precision. A precision of \(10^{-5}\) level is accessible with 40~ab\(^{-1}\) and with more data it would start to approach the \(10^{-6}\) level. This technique would provide the most precise information from the third generation about potential new physics explanations of the muon \(g-2\) \(4\sigma\) anomaly. Additional \(\tau\) and QCD physics programs enabled or enhanced with having polarized electron beams are also discussed in this White Paper. This paper includes a summary of the path forward in R&D and next steps required to implement this upgrade and access its exciting discovery potential.
We report the first measurement of the double-spin asymmetry A{LT} for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized {3}He target. ...The kinematics focused on the valence quark region, 0.16<x<0.35 with 1.4<Q{2}<2.7 GeV{2}. The corresponding neutron A{LT} asymmetries were extracted from the measured {3}He asymmetries and proton over {3}He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g{1T}{q} and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π{-} production on {3}He and the neutron, while our π{+} asymmetries are consistent with zero.
We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries \(B_n\) on \(^{12}\)C and \(^{27}\)Al, obtained with an electron beam polarized transverse to ...its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of \(B_n\) on \(^{12}\)C and provide a first measurement on \(^{27}\)Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average lab scattering angle for both targets was 7.7 degrees, and the average \(Q^2\) for both targets was 0.02437 GeV\(^2\) (Q=0.1561 GeV). The asymmetries are \(B_n\) = -10.68 \(\pm\) 0.90 stat) \(\pm\) 0.57 (syst) ppm for \(^{12}\)C and \(B_n\) = -12.16 \(\pm\) 0.58 (stat) \(\pm\) 0.62 (syst) ppm for \(^{27}\)Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q-dependence of all the far-forward angle (theta < 10 degrees) data from \(^{1}\)H to \(^{27}\)Al can be described by the same slope out to \(Q \approx 0.35\) GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep.
The proposed measurement is a dedicated study of the exclusive electroproduction process,1H(e,e'p)pi0, in the backward-angle regime (u-channel process) above the resonance region. The produced pi0 is ...emitted 180 degrees opposite to the virtual-photon momentum. This study also aims to apply the well-known Rosenbluth separation technique that provides the model-independent differential cross-sections at the never explored u-channel kinematics region. Currently, the "soft-hard transition" in u-channel meson production remains an interesting and unexplored subject. The available theoretical frameworks offer competing interpretations for the observed backward-angle cross section peaks. In a "soft" hadronic Regge exchange description, the backward meson production comes from the interference between nucleon exchange and the meson produced via re-scattering within the nucleon. Whereas in the "hard" GPD-like backward collinear factorization regime, the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes (TDAs), otherwise known as super skewed parton distributions (SuperSPDs). Both TDAs and SPDs are universal non-perturbative objects of nucleon structure accessible only through backward-angle kinematics. The separated cross sections:sigma_T,sigma_L and T/L ratio at Q2=2-6 GeV2, provide a direct test of two predictions from the TDA model. The magnitude and u-dependence of the separated cross sections also provide a direct connection to the re-scattering Regge picture. The extracted interaction radius (from u-dependence) at different Q2 can be used to study the soft-hard transition in the u-channel kinematics. The acquisition of these data will be an important step forward in validating the existence of a backward factorization scheme of the nucleon structure function and establishing its applicable kinematic range.
We report high-precision measurements of the Deeply Virtual Compton
Scattering (DVCS) cross section at high values of the Bjorken variable $x_B$.
DVCS is sensitive to the Generalized Parton ...Distributions of the nucleon, which
provide a three-dimensional description of its internal constituents. Using the
exact analytic expression of the DVCS cross section for all possible
polarization states of the initial and final electron and nucleon, and final
state photon, we present the first experimental extraction of all four
helicity-conserving Compton Form Factors (CFFs) of the nucleon as a function of
$x_B$, while systematically including helicity flip amplitudes. In particular,
the high accuracy of the present data demonstrates sensitivity to some very
poorly known CFFs.
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