arXiv subjects

L. Elouadrhiri

Publications and source records attributed to L. Elouadrhiri.

At least 19 recordsLinked to original sources

arXiv2026

Measurements of $γ_v p \to π^+ π^-p'$ Cross Sections with the CLAS12 Detector for $Q^2$ from 2.4-8.0 GeV$^2$ and $W$ from 1.4-2.1 GeV

This paper reports exclusive cross sections for the $ep \to e'π^+π^-p'$ reaction using the CLAS12 detector at Jefferson Laboratory. The extractions of fully integrated and nine single-differential cross sections are presented for the first time for photon virtualities $Q^2$ from 2.4 to 8.0 GeV$^2$ and center-of-mass energies $W$ from 1.4 to 2.1 GeV, which covers a large part of the nucleon resonance region. These data considerably extend the kinematic reach of previous measurements from CLAS that covered $Q^2$ up to 5.0 GeV$^2$. Exclusive $γ_v p \to π^+ π^-p'$ cross section measurements are of particular importance for the extraction of $γ_vpN^*$ resonance electrocouplings across the $N^*$ spectrum, especially in the mass range above 1.6 GeV where several resonances decay preferentially to the $ππN$ final states. The electrocouplings with extended $Q^2$ coverage expected from these new data will enable an improved understanding of the emergence of $N^*$ mass and structure in the transition from the strongly coupled toward the perturbative QCD regime.

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arXiv2026

First Measurement of Near-Threshold J/ψ Photoproduction on the Neutron

We report the first measurement of the total and t-differential cross sections for near-threshold J/$ψ$ photoproduction on the neutron, obtained with the CLAS12 detector at the Thomas Jefferson National Accelerator Facility. The measurements, performed using a liquid-deuterium target, also provide the incoherent total and t-differential cross sections on the bound proton, enabling the first direct comparison of near-threshold J/$ψ$ photoproduction on bound protons and neutrons. Interpreted within Vector Meson Dominance, holographic QCD, and GPD-based frameworks, the data allow for the investigation of the gluonic structure of bound nucleons. A comparison with free proton results reveals hints of modifications to the gluon structure of nucleons in the nuclear medium, within the assumptions of the extraction and on the underlying production mechanism. The comparison of bound neutron and bound proton cross sections provides new constraints on the near-threshold J/$ψ$ production mechanism, which is crucial in order to establish J/$ψ$ photoproduction as a probe of the nucleon's gluonic structure.

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arXiv2026

Multi-Differential DVCS Cross Section Measurement on the Proton in the Valence Region with CLAS12

We report the measurement of the four-fold differential cross section of deeply virtual Compton scattering (DVCS) on the proton using a longitudinally polarized 10.6 GeV CEBAF electron beam incident on a liquid-hydrogen target with the CLAS12 detector. The analysis provides 1312 data points, expanding the measured phase space in the valence quark region, 0.06 < $x_B$ < 0.58, 1.00 < $Q^2$ < 5.76 GeV$^2$, and 0.11 < $|t|$ < 1.00 GeV$^2$. DVCS cross section measurements directly constrain the real part of the DVCS amplitude through its interference with the Bethe-Heitler process, making them essential inputs to global extractions of the Compton Form Factors (CFFs), particularly the dominant CFF $H$. These data improve sensitivity to these observables and can contribute to future determinations of the proton's internal mechanical structure.

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arXiv2026

First measurement of polarized spin-density matrix elements and differential cross sections d$σ$/d$t$ in $ω$~photoproduction off the proton for $2.7 < E_γ< 5.2$ GeV using CLAS at Jefferson Lab

We report on the differential cross sections d$σ$/d$t$, the unpolarized spin-density matrix elements $ρ^0_{00}$, $ρ^0_{1-1}$, Re\,$ρ^0_{10}$, and the first extraction of the polarized elements Im\,$ρ^3_{10}$, Im\,$ρ^3_{1-1}$ for the reaction $γp\to pω$ using the CLAS spectrometer at Jefferson Laboratory. The $ω$~mesons were detected in their dominant charged decay mode, $ω\to π^+π^-π^0$, and all $t$-dependent results are presented in a fine binning for incident photon energies between 2.73 and 5.16~GeV (corresponding to the center-of-mass energy range $W \in [\,2.45,3.25\,]$~GeV). All matrix elements are first measurements for $-t > 0.6$~GeV$^2$. Moreover, differential cross sections d$σ$/d(cos\,$Θ_{\rm \,c.m.}^{\,ω}$) and the corresponding angle-dependent unpolarized spin-density matrix elements in the Adair frame are presented for the incident photon energy range 1.56--3.80~GeV (corresponding to $W \in [\,1.95,2.83\,]$~GeV). These new $ω$~photoproduction data are consistent with earlier CLAS results but extend the energy range well beyond the nucleon resonance region into the Regge regime. The comparison with Regge-theory-based model predictions shows that the new data impose more stringent constraints on our understanding of $ω$~photoproduction.

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arXiv2026

Measurement of the near-threshold J$/ψ$ photoproduction cross section with the CLAS12 experiment

We present measurements of the total and differential cross sections for near-threshold J/$ψ$ photoproduction obtained with the CLAS12 detector at the Thomas Jefferson National Accelerator Facility. The results are based on data collected during the Fall 2018 and Spring 2019 running periods, using electron beams with energies of 10.6 and 10.2 GeV, respectively, scattered off a liquid-hydrogen target. Near-threshold J$/ψ$ photoproduction offers a unique sensitivity to the strong interaction in the non-perturbative regime of Quantum Chromodynamics (QCD). The energy dependence of the cross section constrains the underlying J$/ψ$ production mechanisms, including multi-gluon exchange and potential baryonic excitations. Additionally, the $t$-dependence of the differential cross section can be related to the transverse spatial distribution of gluons in the proton, providing critical input for theoretical descriptions of the gluonic structure of the proton. An interpretation of the results in terms of the gluon content of the proton is presented, providing new experimental constraints on QCD-inspired models of the proton structure and the role of gluonic degrees of freedom in hadronic mass generation.

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arXiv2026

Electro- and photoproduction of muon pairs with $μ$CLAS12: Double Deeply Virtual Compton Scattering, Timelike Compton Scattering, and $J/ψ$ production

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV (CLAS12) at the Thomas Jefferson National Accelerator Facility has played a central role in advancing the understanding of nucleon and nuclear structure. As increasingly precise data become available, new physics opportunities emerge that extend beyond the current capabilities of CLAS12. In this article, a program to explore the quark and gluon structure of the nucleon through di-muon electro- and photoproduction is presented. Its primary focus is the measurement of beam-spin asymmetries in Double Deeply Virtual Compton Scattering, $ep \rightarrow e^\prime μ^+ μ^-p^\prime $. By independently varying the incoming and outgoing photon virtualities and momentum transfer, the DDVCS measurement provides access to the Generalized Parton Distributions over their full three-dimensional phase space, extending beyond the kinematic constraints of Deeply Virtual Compton Scattering and Timelike Compton Scattering. In addition, the large acceptance and high luminosity of the $μ$CLAS12 experiment will enable precision measurements of near-threshold $J/ψ$ production and high-statistics studies of Timelike Compton Scattering.

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arXiv2026

First Study of the Nuclear Response to Fast Hadrons via Angular Correlations between Pions and Slow Protons in Electron-Nucleus Scattering

We report on the first measurement of angular correlations between high-energy pions and slow protons in electron-nucleus ($eA$) scattering, providing a new probe of how a nucleus responds to a fast-moving quark. The experiment employed the CLAS detector with a 5-GeV electron beam incident on deuterium, carbon, iron, and lead targets. For heavier nuclei, the pion-proton correlation function is more spread-out in azimuth than for lighter ones, and this effect is more pronounced in the $πp$ channel than in earlier $ππ$ studies. The proton-to-pion yield ratio likewise rises with nuclear mass, although the increase appears to saturate for the heaviest targets. These trends are qualitatively reproduced by state-of-the-art $eA$ event generators, including BeAGLE, eHIJING, and GiBUU, indicating that current descriptions of target fragmentation rest on sound theoretical footing. At the same time, the precision of our data exposes model-dependent discrepancies, delineating a clear path for future improvements in the treatment of cold-nuclear matter effects in $eA$ scattering.

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arXiv2026

Frascati 22 GeV Workshop Summary

This document summarizes the outcomes of the "Science at the Luminosity Frontier: Jefferson Lab at 22 GeV" workshop, held at the INFN Laboratori Nazionali di Frascati in December 2024. The primary goal of the workshop was to critically assess and refine the scientific case for a proposed energy upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) to 22 GeV. This document intends to capture the progress on developing the scientific case since the publication of a lengthy "White Paper" in summer 2024 signed by about 450 authors.

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arXiv2026

Measurement of the nucleon spin structure functions for 0.01<$Q^2$<1 GeV$^2$ using CLAS

The spin structure functions of the proton and the deuteron were measured during the EG4 experiment at Jefferson Lab in 2006. Data were collected for longitudinally polarized electron scattering off longitudinally polarized NH$_3$ and ND$_3$ targets, for $Q^2$ values as small as 0.012 and 0.02 GeV$^2$, respectively, using the CEBAF Large Acceptance Spectrometer (CLAS). This is the archival paper of the EG4 experiment that summaries the previously reported results of the polarized structure functions $g_1$, $A_1F_1$, and their moments $\overline Γ_1$, $\overline γ_0$, and $\overline I_{TT}$, for both the proton and the deuteron. In addition, we report on new results on the neutron $g_1$ extracted by combining proton and deuteron data and correcting for Fermi smearing, and on the neutron moments $\overline Γ_1$, $\overline γ_0$, and $\overline I_{TT}$ formed directly from those of the proton and the deuteron. Our data are in good agreement with the Gerasimov-Drell-Hearn sum rule for the proton, deuteron, and neutron. Furthermore, the isovector combination was formed for $g_1$ and the Bjorken integral $\overline Γ_1^{p-n}$, and compared to available theoretical predictions. All of our results provide for the first time extensive tests of spin observable predictions from chiral effective field theory ($χ$EFT) in a $Q^2$ range commensurate with the pion mass. They motivate further improvement in $χ$EFT calculations from other approaches such as the lattice gauge method.

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arXiv2025

Multidimensional Measurements of Beam Single Spin Asymmetries in Semi-inclusive Deep-inelastic Charged Kaon Electroproduction off Protons in the Valence Region

Measurements of beam single spin asymmetries in semi-inclusive deep inelastic electron scattering (SIDIS) with positively charged kaons off protons have been performed with 10.6 and 10.2 GeV incident electron beams using the CLAS12 spectrometer at Jefferson Lab. We report an analysis of the electroproduction of positively charged kaons over a large kinematic range of fractional energy, Bjorken $x$, transverse momentum, and photon virtualities $Q^2$ ranging from 1 GeV$^2$ up to 6 GeV$^2$. This is the first published multi-dimensionally binned CLAS12 measurement of a kaon SIDIS single spin asymmetry in the valence quark regime. The data provide constraints on the structure function ratio $F_{LU}^{\sinϕ}/F_{UU}$, where $F_{LU}^{\sinϕ}$ is a quantity with a leading twist of twist-3 that can reveal novel aspects of the quark-gluon correlations within the nucleon. The impact of the data on understanding the underlying reaction mechanisms and their kinematic variation is explored using theoretical models for the different contributing twist-3 parton distribution functions (PDFs) and fragmentation functions (FFs).

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arXiv2025

Measurement of Beam-Recoil Observables $C_x$ and $C_z$ for $K^+Λ$ Photoproduction

Exclusive photoproduction of $K^+ Λ$ final states off a proton target has been an important component in the search for missing nucleon resonances and our understanding of the production of final states containing strange quarks. Polarization observables have been instrumental in this effort. The current work is an extension of previously published CLAS results on the beam-recoil transferred polarization observables $C_x$ and $C_z$. We extend the kinematic range up to invariant mass $W=3.33$~GeV from the previous limit of $W=2.5$~GeV with significantly improved statistical precision in the region of overlap. These data will provide for tighter constraints on the reaction models used to unravel the spectrum of nucleon resonances and their properties by not only improving the statistical precision of the data within the resonance region, but also by constraining $t$-channel processes that dominate at higher $W$ but extend into the resonance region.

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arXiv2025

Proton Transparency and Neutrino Physics: New Methods and Modeling

Extracting accurate results from neutrino oscillation and cross section experiments requires accurate simulation of the neutrino-nucleus interaction. The rescattering of outgoing hadrons (final state interactions) by the rest of the nucleus is an important component of these interactions. We present a new measurement of proton transparency (defined as the fraction of outgoing protons that emerge without significant rescattering) using electron-nucleus scattering data recorded by the CLAS detector at Jefferson Laboratory on helium, carbon, and iron targets. This analysis by the Electrons for Neutrinos ($e4ν$) collaboration uses a new data-driven method to extract the transparency. It defines transparency as the ratio of electron-scattering events with a detected proton to quasi-elastic electron-scattering events where a proton should have been knocked out. Our results are consistent with previous measurements that determined the transparency from the ratio of measured events to theoretically predicted events. We find that the GENIE event generator, which is widely used by oscillation experiments to simulate neutrino-nucleus interactions, needs to better describe both the nuclear ground state and proton rescattering in order to reproduce our measured transparency ratios, especially at lower proton momenta.

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arXiv2025

Recoil Polarization in $K^+Y$ Electroproduction in the Nucleon Resonance Region with CLAS12

Hyperon recoil polarization measurements for the exclusive electroproduction of $K^+Λ$ and $K^+Σ^0$ final states from an unpolarized proton target have been carried out using the CLAS12 spectrometer at Jefferson Laboratory. The measurements at beam energies of 6.535~GeV and 7.546~GeV span the range of four-momentum transfer $Q^2$ from 0.3 to 4.5~GeV$^2$ and invariant mass $W$ from 1.6 to 2.4~GeV, while covering the full center-of-mass angular range of the $K^+$. These new $Λ$ polarization observables extend the existing data in a similar kinematic range but from a significantly larger dataset. However, they represent the first electroproduction measurements of this observable for the $Σ^0$. These data will allow for better exploration of the reaction mechanism in strangeness production, for further understanding of the spectrum and structure of excited nucleon states that couple to $KY$, and for improved insight into the strong interaction in the non-perturbative domain.

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arXiv2025

Inclusive Electron Scattering in the Resonance Region off a Hydrogen Target with CLAS12

Inclusive electron scattering cross sections off a hydrogen target at a beam energy of 10.6 GeV have been measured with data collected from the CLAS12 spectrometer at Jefferson Laboratory. These first absolute cross sections from CLAS12 cover a wide kinematic area in invariant mass W of the final state hadrons from the pion threshold up to 2.5 GeV for each bin in virtual photon four-momentum transfer squared $Q^2$ from 2.55 to 10.4~GeV$^2$ owing to the large scattering angle acceptance of the CLAS12 detector. Comparison of the cross sections with the resonant contributions computed from the CLAS results on the nucleon resonance electroexcitation amplitudes has demonstrated a promising opportunity to extend the information on their $Q^2$ evolution up to 10 GeV$^2$. Together these results from CLAS and CLAS12 offer good prospects for probing the nucleon parton distributions at large fractional parton momenta $x$ for $W$ < 2.5 GeV, while covering the range of distances where the transition from the strongly coupled to the perturbative regimes is expected.

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arXiv2024

First Measurement of Deeply Virtual Compton Scattering on the Neutron with Detection of the Active Neutron

Measuring Deeply Virtual Compton Scattering on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of Generalized Parton Distributions (GPDs). Neutron targets play a complementary role to transversely polarized proton targets in the determination of the GPD $E$. This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks' angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the GPDs $H$ and $E$.

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arXiv2024

Colloquium: Gravitational Form Factors of the Proton

The physics of the gravitational form factors of the proton, and their understanding within quantum chromodynamics, has advanced significantly in the past two decades through both theory and experiment. This Colloquium provides an overview of this progress, highlights the physical insights unveiled by studies of gravitational form factors, and reviews their interpretation in terms of the mechanical properties of the proton.

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arXiv2023

Beam Charge Asymmetries for Deeply Virtual Compton Scattering on the Proton at CLAS12

The parameterization of the nucleon structure through Generalized Parton Distributions (GPDs) shed a new light on the nucleon internal dynamics. For its direct interpretation, Deeply Virtual Compton Scattering (DVCS) is the golden channel for GPDs investigation. The DVCS process interferes with the Bethe-Heitler (BH) mechanism to constitute the leading order amplitude of the $eN \to eNγ$ process. The study of the $epγ$ reaction with polarized positron and electron beams gives a complete set of unique observables to unravel the different contributions to the $ep γ$ cross section. This separates the different reaction amplitudes, providing a direct access to their real and imaginary parts which procures crucial constraints on the model dependences and associated systematic uncertainties on GPDs extraction. The real part of the BH-DVCS interference amplitude is particularly sensitive to the $D$-term which parameterizes the Gravitational Form Factors of the nucleon. The separation of the imaginary parts of the interference and DVCS amplitudes provides insights on possible higher-twist effects. We propose to measure the unpolarized and polarized Beam Charge Asymmetries (BCAs) of the $\vec{e}^{\pm}p \to e^{\pm}p γ$ process on an unpolarized hydrogen target with {\tt CLAS12}, using polarized positron and electron beams at 10.6 GeV. The azimuthal and $t$-dependences of the unpolarized and polarized BCAs will be measured over a large $(x_B,Q^2)$ phase space using a 100 day run with a luminosity of 0.66$\times 10^{35}$cm$^{-2}\cdot$s$^{-1}$.

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arXiv2023

The mechanical radius of the proton

We present the first determination of the proton mechanical radius. The result was obtained by employing a novel theoretical approach that connects experimental data of deeply virtual Compton scattering with the spin = 2 interaction that is characteristic of gravity coupling with matter. We find that the proton mechanical radius is significantly smaller than its charge radius, consistent with the latest Lattice QCD computation.

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