arXiv subjects

A. Usman

Publications and source records attributed to A. Usman.

7 recordsLinked to original sources

arXiv2025

Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton

Deep exclusive meson production (DEMP) reactions, such as $p(\vec{e},e'\pi^+)n$, provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive $p(\vec{e},e'\pi^+)n$ reaction, as measured in the KaonLT experiment at Jefferson Lab Hall C. A 10.6 GeV longitudinally polarized electron beam was incident on an unpolarized liquid hydrogen target, and the scattered electron and produced meson were detected in two magnetic focusing spectrometers, enabling precision cross section measurements. The cross section ratio $\sigma_{LT'}/\sigma_0$ was extracted from the beam-spin asymmetry $A_{LU}$. The $t$-dependence of $\sigma_{LT'}/\sigma_0$ was determined at fixed $Q^2$ and $x_B$ over a range of kinematics from $2 2$ GeV). Furthermore, these data are combined with recent results from CLAS/CLAS12 to determine the $Q^2$-dependence of $\sigma_{LT'}/\sigma_0$ at two ($x_B$, $t$) settings. This was fairly flat, with $Q^2$ not having a measurable effect on the value of $\sigma_{LT'}/\sigma_0$ in the range explored. Results are compared to predictions from the generalized parton distribution (GPD) formalism, which relies explicitly on hard/soft factorization, and Regge formalism. The Regge models better predict $\sigma_{LT'}/\sigma_0$, which suggests that the factorization regime is not yet reached.

nucl-ex↗

arXiv2025

The SHMS 11 GeV/c Spectrometer in Hall C at Jefferson Lab

The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnetic spectrometer comprised of a series of new superconducting magnets which transport charged particles through an array of triggering, tracking, and particle-identification detectors that measure momentum, energy, angle and position in order to allow kinematic reconstruction of the events back to their origin at the scattering target. The detector system is protected from background radiation by a sophisticated shielding enclosure. The entire spectrometer is mounted on a rotating support structure which permits measurements to be taken with a large acceptance over laboratory scattering angles from 5.5 to 40 degrees, thus allowing a wide range of low cross-section experiments to be conducted. These experiments complement and extend the previous Hall C research program to higher energies.

physics.ins-det↗

arXiv2025

Studying the Strangeness $D$-Term in Hall C via Exclusive $\phi$ Electroproduction

We propose a measurement of exclusive electroproduction of $\phi$ mesons near threshold in Hall C. We will measure the |t|-dependence of the exclusive $\phi$ electroproduction cross section, which has recently been proposed as an observable sensitive to the strangeness $D$-term. The contribution of strangeness to the total $D$-term is presently unknown, with different arguments favoring $D_s$ being large, being small, or even having opposite sign from the total $D$-term. Our exploratory measurement is designed to distinguish between these hypotheses. If $D_s$ turns out to be small, $\phi$ electroproduction can be used to study the gluon $D$-term. In addition, this dataset will allow us to perform measurements of other exclusive meson final states, including the first measurement of $\eta'$ electroproduction and multi-differential measurements of $\eta$ and $\omega$ electroproduction.

nucl-ex↗

arXiv2024

Quasielastic $\overrightarrow{^{3}\mathrm{He}}(\overrightarrow{e},{e'})$ Asymmetry in the Threshold Region

A measurement of the double-spin asymmetry from electron-$^{3}$He scattering in the threshold region of two- and three-body breakup of $^{3}$He was performed at Jefferson Lab, for Q$^{2}$ values of 0.1 and 0.2 (GeV/$c$)$^{2}$. The results of this measurement serve as a stringent test of our understanding of few-body systems. When compared with calculations from plane wave impulse approximation and Faddeev theory, we found that the Faddeev calculations, which use modern nuclear potentials and prescriptions for meson-exchange currents, demonstrate an overall good agreement with data.

nucl-ex↗

arXiv2024

DEMPgen: Physics event generator for Deep Exclusive Meson Production at Jefferson Lab and the EIC

There is increasing interest in deep exclusive meson production (DEMP) reactions, as they provide access to Generalized Parton Distributions over a broad kinematic range, and are the only means of measuring pion and kaon charged electric form factors at high $Q^2$. Such investigations are a particularly useful tool in the study of hadronic structure in QCD's transition regime from long-distance interactions described in terms of meson-nucleon degrees of freedom, to short-dist ance interactions governed by hard quark-gluon degrees of freedom. To assist the planning of future experimental investigations of DEMP reactions in this transition regime, such as at Jefferson Lab and the Electron-Ion Collider (EIC), we have written a special purpose event generator, DEMPgen. Several types of DEMP reactions can be generated: $t$-channel $p(e,e^{\prime}\pi^+)n$, $p(e,e^{\prime}K^+)\Lambda[\Sigma^0]$, and $\vec{n}(e,e^{\prime}\pi^-)p$ from a polarized $^3$He target. DEMPgen is modular in form, so that additional reactions can be added over time. The generator produces kinematically-complete reaction events which are absolutely-normalized, so that projected event rates can be predicted, and detector resolution requirements studied. The event normalization is based on parameterizations of theoretical models, appropriate to the kinematic regime under study. Both fixed target modes and collider beam modes are supported. This paper presents the structure of the generator, the model parameterizations used for absolute event weighting, the kinematic distributions of the generated particles, some initial results using the generator, and instructions for its use.

hep-ph↗

arXiv2023

Detector Requirements and Simulation Results for the EIC Exclusive, Diffractive and Tagging Physics Program using the ECCE Detector Concept

This article presents a collection of simulation studies using the ECCE detector concept in the context of the EIC's exclusive, diffractive, and tagging physics program, which aims to further explore the rich quark-gluon structure of nucleons and nuclei. To successfully execute the program, ECCE proposed to utilize the detecter system close to the beamline to ensure exclusivity and tag ion beam/fragments for a particular reaction of interest. Preliminary studies confirmed the proposed technology and design satisfy the requirements. The projected physics impact results are based on the projected detector performance from the simulation at 10 or 100 fb^-1 of integrated luminosity. Additionally, a few insights on the potential 2nd Interaction Region can (IR) were also documented which could serve as a guidepost for the future development of a second EIC detector.

physics.ins-det↗

arXiv2021

Backward-angle Exclusive pi0 Production above the Resonance Region

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.

nucl-ex↗