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V. I. Mokeev

Publications and source records attributed to V. I. Mokeev.

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

Measurements of $γ_v p \to π^+ π^- p'$ Cross Sections with the CLAS Detector for $Q^{2}$ from 2.0--5.0~GeV$^{2}$ and $W$ from 1.400--2.125~GeV

Observables in the electroproduction of the $π^+π^-p$ reaction channel off the proton that are sensitive to the polarization of the virtual photon are presented for the first time in addition to the extraction of the nine single-differential and fully integrated cross sections within the kinematics area of 2.0~GeV$^2 < Q^2 < 5.0$~GeV$^2$ and 1.400~GeV $< W < 2.125$~GeV measured with the CLAS detector in Hall B at Jefferson Lab. The extraction of the unpolarized cross sections has been considerably improved in comparison with previously published results from this same dataset, offering finer binning over the five-dimensional hadronic reaction phase space, and including essential advances in the acceptance evaluation by implementing a new technique to stabilize the cross section extraction and minimize the systematic uncertainty associated with the simulation statistics. These improvements are of particular importance for the extraction of the $γ_v p N^*$ electrocouplings from these data.

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arXiv2026

First Results on Nucleon Resonance Electroexcitation Amplitudes from $ep \to e'π^+π^-p'$ Cross Sections at $W$ from $1.56-1.76$ GeV and $Q^2$ from $2.0-5.0$ GeV$^2$

The first results on the electroexcitation amplitudes or the $γ_vpN^*$ electrocouplings for nucleon resonances ($N^*$s) in the third resonance region are presented. They were obtained from $π^+π^-p$ electroproduction differential cross sections measured with the CLAS detector and analyzed using the Jefferson Lab-Moscow State University (JM) reaction model. The analysis covers the invariant mass range of the final-state hadrons $W$ from 1.56 to 1.76~GeV and virtual photon four-momentum squared $Q^2$ from 2.0 to 5.0~GeV$^2$. Consistent results on the electroexcitation amplitudes of the $N(1675)5/2^-$ and $N(1680)5/2^+$ obtained from independent analyses of both $πN$ and $π^+π^-p$ final states, demonstrate the capability of reaction models to extract the $γ_v p N^*$ electrocouplings for $N^*$s in the third resonance region. Also, for the first time, the electrocouplings of the $Δ(1700)3/2^-$ and $N(1720)3/2^+$, which predominantly decay into $ππN$ final states, have become available for $Q^2 > 2.0$~GeV$^2$. Finally, contributions from a new $N'(1720)3/2^+$ baryon state to the $π^+π^-p$ differential cross sections have been observed for $Q^2 < 5.0$~GeV$^2$. The new results on resonance electrocouplings in the third resonance region offer new opportunities to explore various aspects of the strong QCD regime responsible for the generation of nucleon excited states, in particular, shedding light on the emergence of hadron mass in connection with dynamical chiral symmetry breaking.

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arXiv2026

Quark--hadron duality in inclusive electron--proton scattering at high $Q^{2}$: structure functions and truncated moments from CLAS12

We present a high-precision study of quark--hadron duality in inclusive electron--proton scattering in the nucleon resonance region, extending to $Q^2\approx10~\mathrm{GeV}^2$, based on recent CLAS12 cross-section measurements at Jefferson Lab. The data, taken with a 10.6~GeV beam, span $2.55 \le Q^2 \le 10.4~\mathrm{GeV}^2$ and cover the full resonance region up to $W\approx2.5~\mathrm{GeV}$. To reach the CLAS12 kinematics, we develop a phenomenological high-$Q^2$ extension of the Argonne--Osaka (ANL-Osaka) dynamical coupled-channels framework, anchored to the original calculation at $Q_0^2=2.774~\mathrm{GeV}^2$ and constrained by the measured cross sections. This enables an ANL-Osaka-constrained longitudinal--transverse decomposition and determination of the proton structure function $F_2(W,Q^2)$, from which we evaluate $W$-truncated Cornwall--Norton moments $M_2(Q^2)$. Comparison with the CJ15 global QCD analysis, including target-mass and higher-twist corrections, shows consistency at the cross-section, structure-function, and truncated-moment levels, providing quantitative evidence for both local and global quark--hadron duality at substantially higher $Q^2$ than previously explored. We further identify a threshold effect in the partonic calculation: the finite-$Q^2$ corrections do not enforce the physical pion-production threshold, and the residual discrepancy in the first resonance region is consistent with this effect rather than a breakdown of duality. Within the coupled-channel description, the single-pion channel alone underestimates the inclusive resonance-region strength above the $Δ(1232)$, which is carried predominantly by the multi-meson channels, as required for duality.

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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

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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arXiv2025

Roper Resonance Structure and Exploration of Emergent Hadron Mass from CLAS Electroproduction Data

The $N(1440)1/2^+$ nucleon resonance, first identified in 1964 by L.D. Roper and collaborators in analyses of $πN$ hadroproduction data have continued to provide pivotal insights that serve to advance our understanding of nucleon excited states. In this contribution, we present results from studies of the structure of the Roper resonance based on exclusive $πN$ and $π^+π^-p$ electroproduction data measured with the CLAS detector at Jefferson Lab. These analyses have revealed the Roper resonance as a complex interplay between an inner core of three dressed quarks and an external meson--baryon cloud. Analyses of the CLAS results on the evolution of the Roper resonance electroexcitation amplitudes with photon virtuality $Q^2$, within the framework of the Continuum Schwinger Method, have conclusively demonstrated the capability to gain insight into the strong interaction dynamics responsible for generating more than 98\% of hadron mass. Further extension of such studies to higher $Q^2$--through experiments currently underway with the CLAS12 detector and in the future with a potential CEBAF energy upgrade to 22 GeV--offers the only foreseeable opportunity to explore the full range of distances where the dominant portion of hadron mass and resonance structure emerges.

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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

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

Insight into Emergence of Hadron Mass from $\boldmath N^*$ Electroexcitation Amplitudes

The emergence of hadron mass represents one of the most challenging and still open problems in contemporary hadron physics. The results on the nucleon resonance electroexcitation amplitudes available from the CLAS data on $πN$ and $π^+π^-p$ electroproduction analyzed within the continuum Schwinger method open up a new avenue for gaining insight into the strong interaction dynamics that are responsible for the generation of the dominant part of hadron mass. Future prospects of these studies in experiments of the 12-GeV era with CLAS12 and after a potential increase of the CEBAF energy up to 22 GeV will offer a unique opportunity to explore the full range of distances where the dominant part of hadron mass and $N^*$ structure emerge from QCD.

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arXiv2023

Toward a generative modeling analysis of CLAS exclusive $2π$ photoproduction

AI-supported algorithms, particularly generative models, have been successfully used in a variety of different contexts. In this work, we demonstrate for the first time that generative adversarial networks (GANs) can be used in high-energy experimental physics to unfold detector effects from multi-particle final states, while preserving correlations between kinematic variables in multidimensional phase space. We perform a full closure test on two-pion photoproduction pseudodata generated with a realistic model in the kinematics of the Jefferson Lab CLAS g11 experiment. The overlap of different reaction mechanisms leading to the same final state associated with the CLAS detector's nontrivial effects represents an ideal test case for AI-supported analysis. Uncertainty quantification performed via bootstrap provides an estimate of the systematic uncertainty associated with the procedure. The test demonstrates that GANs can reproduce highly correlated multidifferential cross sections even in the presence of detector-induced distortions in the training datasets, and provides a solid basis for applying the framework to real experimental data.

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arXiv2023

First Results on Nucleon Resonance Electroexcitation Amplitudes from $ep\to e'π^+π^-p'$ Cross Sections at $W$ from 1.4-1.7 GeV and $Q^2$ from 2.0-5.0 GeV$^2$

The electroexcitation amplitudes or $γ_vpN^*$ electrocouplings of the $N(1440)1/2^+$, $N(1520)3/2^-$, and $Δ(1600)3/2^+$ resonances were obtained for the first time from the $ep \to e'π^+π^-p'$ differential cross sections measured with the CLAS detector at Jefferson Lab within the range of invariant mass $W$ of the final state hadrons from 1.4--1.7 GeV for photon virtualities $Q^2$ from 2.0--5.0 GeV$^2$. The electrocouplings were determined in independent fits of the $π^+π^-p$ cross sections within three overlapping $W$ intervals with a substantial contribution from each of the three resonances listed above. Consistent results on the electrocouplings extracted from the data in these $W$ intervals provide evidence for their reliable extraction. These studies extend information on the electrocouplings of the $N(1440)1/2^+$ and $N(1520)3/2^-$ available from this channel over a broader range of $Q^2$. The electrocouplings of the $Δ(1600)3/2^+$, which decays preferentially into $ππN$ final states, have been determined for the first time. Our results provide further evidence for the structure of these resonances in terms of an interplay between the inner core of three dressed quarks and an external meson-baryon cloud.

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arXiv2023

Resonant contributions to polarized proton structure functions

Nucleon resonance contributions to the polarized proton $g_1$ and $g_2$ structure functions are computed from resonance electroexcitation amplitudes extracted from CLAS exclusive meson electroproduction data. Including resonances in the mass range up to 1.75 GeV, and taking into account the interference between excited states, we compare the resonant contributions with the polarized proton structure function and polarization asymmetry data from Jefferson Lab 6 GeV measurements. All resonance-like structure observed in the polarized structure functions and asymmetries can be attributed to the resonant contributions, confirming their essential role in the behavior of $g_1$ and $g_2$ in the resonant region over the entire range $Q^2 < 7.5$ GeV$^2$ covered by the measurements. Comparing the resonance contributions with the $g_1$ and $g_2$ structure functions computed from parton distribution functions extrapolated from the deep-inelastic region, we also quantify the degree to which quark-hadron duality holds for $g_1$ and $g_2$ and their moments.

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arXiv2023

Polarized proton structure in the resonance region

In view of the precise data available on inclusive polarized electron scattering off polarized proton targets in the nucleon resonance excitation region, we compare these results with the coherent sum of resonant contributions to the polarized structure function $g_1$ and virtual photon asymmetry $A_1$. To this goal, we employ the nucleon resonance electroexcitation amplitudes determined for photon virtualities $Q^2$ $<$ 5.0 GeV$^2$ from analyses of the CLAS data on exclusive electroproduction off protons in the resonance region. Most of the well established resonances of four star PDG status in the mass range up to 1.75~GeV are included. We find that the resonance-like structures observed in the inclusive $g_1$ data are related to the resonant contributions in the entire range of photon virtuality $Q^2$ where the data on $g_1$ are available. In the range of invariant mass of the final hadron system $W$ $>$ 1.5 GeV, the data on the asymmetry $A_1$ are well reproduced even when accounting for resonant contributions only, especially for the larger values of $Q^2$ and energies analysed. This observation offers an interesting hint to quark-hadron duality seen in polarized inclusive electron scattering observables.

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arXiv2023

Exclusive $π^{-}$ Electroproduction off the Neutron in Deuterium in the Resonance Region

New results for the exclusive and quasi-free cross sections off neutrons bound in deuterium $γ_vn(p) \rightarrow pπ^{-} (p)$ are presented over a wide final state hadron angle range with a kinematic coverage of the invariant mass ($W$) up to 1.825 GeV and the virtual photon four-momentum transfer squared ($Q^{2}$) from 0.4 to 1.0 GeV$^2$. The exclusive structure functions were extracted and their Legendre moments were obtained. Final-state-interaction contributions have been kinematically separated from the extracted quasi-free cross sections off bound neutrons solely based on the analysis of the experimental data. These new results will serve as long-awaited input for phenomenological analyses to extract the $Q^{2}$ evolution of previously unavailable $n \to N^{*}$ electroexcitation amplitudes and to improve state-of-the-art models of neutrino scattering off nuclei by augmenting the already available results from free protons.

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arXiv2022

Observation of azimuth-dependent suppression of hadron pairs in electron scattering off nuclei

We present the first measurement of di-hadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the GiBUU model, which suggests that hadrons form near the nuclear surface and undergo multiple-scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei

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arXiv2022

Symplectic Effective Field Theory for Nuclear Structure Studies

A Symplectic Effective Field Theory that unveils the observed emergence of symplectic symmetry in atomic nuclei is advanced. Specifically, starting from a simple extension of the harmonic-oscillator Lagrangian, an effective field theory applied against symplectic basis states is shown to yield a Hamiltonian system with one fitted parameter. The scale of the system can be determined self consistently as the ratio of the average volume of a nucleus assumed to be spherical to its volume as determined by the average number of oscillator quanta, which is stretched by the fact that the plane-wave solution satisfies the equations of motion at every order without the need for perturbative corrections. As an application of the theory, results for 20Ne, 22Ne and 22Mg are presented that yield energy spectra, B(E2) values, and matter radii in good agreement with experimentally measured results.

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