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Niculescu, G. [James Madison University]

Publications and source records attributed to Niculescu, G. [James Madison University].

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Longitudinal spin transfer to Ξ› hyperons in semi-inclusive deep inelastic scattering with the CLAS12 spectrometer

The polarization of Ξ› hyperons is preserved in the angular distribution of their decay products. This property allows one to study the spin structure of the Ξ›. In semi-inclusive deep inelastic scattering where a high energy lepton interacts with a nucleon target and one or more hadrons and the scattered lepton are detected in the final state, the probability for a struck quark to impart the polarization of the lepton to the Ξ› may be measured. In particular, in electron-proton scattering this quantity may be related to the longitudinal light quark polarization of the Ξ›. Currently, limited experimental data cannot discriminate between different models of Ξ› spin structure. This work reports on the measurement of the longitudinal spin transfer 𝐷$^{Ξ›}_{𝐿⁒𝐿′}$ to the Ξ› using data taken by the CLAS12 spectrometer at Jefferson Lab with a 10.6 GeV longitudinally polarized electron beam and an unpolarized hydrogen target. This measurement is the most precise to date, and, in comparison with theory predictions, it offers valuable insight into the relative dominance of current and target fragmentation in Ξ› production.

deep inelastic scattering↗
DOE OSTI2026

Flavor, transverse momentum, and azimuthal dependence of charged pion multiplicities in semi-inclusive deep-inelastic scattering with 10.6 GeV electrons

Measurements of semi-inclusive deep-inelastic scattering multiplicities for πœ‹ + and πœ‹ βˆ’ from proton and deuteron targets are reported on a grid of hadron kinematic variables 𝑧, 𝑃 𝑇 , and πœ™* for leptonic kinematic variables in the range 0.3<π‘₯<0.6 and 3<𝑄 2 <5GeV 2 . Data were acquired in 2018 and 2019 at Jefferson Lab Hall C with a 10.6 GeV electron beam impinging on 10-cm-long liquid hydrogen and deuterium targets. Scattered electrons and charged pions were detected in the High Momentum Spectrometer and Super High Momentum Spectrometer, respectively. The multiplicities were fitted for each bin in (π‘₯,𝑄 2 ,𝑧,𝑃𝑑) to extract the πœ™*β€”independent 𝑀 0 and the azimuthal modulations ⟨cos⁑(πœ™*)⟩ and ⟨cos⁑(2β’πœ™*)⟩. The 𝑃𝑑 dependence of the 𝑀 0 results was found to be remarkably consistent for the four cases studied: π‘’β’π‘β†’π‘’β’πœ‹ + ⁒𝑋, π‘’β’π‘β†’π‘’β’πœ‹ βˆ’ ⁒𝑋, π‘’β’π‘‘β†’π‘’β’πœ‹ + ⁒𝑋, π‘’β’π‘‘β†’π‘’β’πœ‹ βˆ’ ⁒𝑋 over the range 0GeV<𝑃 𝑑 <0.4GeV, as were the multiplicities evaluated near πœ™*=180∘ over the extended range 0GeV<𝑃 𝑑 <0.7GeV. The Gaussian widths of the 𝑃 𝑑 dependence exhibit a quadratic increase with 𝑧. The cos⁑(πœ™*) modulations were found to be consistent with zero for πœ‹ + , in agreement with previous world data, while the πœ‹ βˆ’ moments were, in many cases, significantly greater than zero. The cos⁑(2β’πœ™*) modulations were found to be consistent with zero. The higher statistical precision of this dataset of about 20 000 individual multiplicity values, compared with previously published data, should allow improved determinations of quark transverse momentum distributions and higher twist contributions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurement of beam-recoil observables 𝐢 π‘₯ and 𝐢 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 𝐢 π‘₯ and 𝐢 𝑧 . Here, we extend the kinematic range up to invariant mass π‘Š = 3.33 GeV from the previous limit of π‘Š = 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 constraining 𝑑-channel processes that dominate at higher π‘Š but extend into the resonance region.

Electrons↗
DOE OSTI2025

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 π‘₯, transverse momentum, and photon virtualities 𝑄 2 ranging from 1 GeV 2 up to 6 GeV 2 . This is the first published multidimensionally binned CLAS12 measurement of a kaon SIDIS single-spin asymmetry in the valence quark regime. The data provide constraints on the structure function ratio $𝐹^{sin \spaceπœ™}_{πΏβ’π‘ˆ}$⁑/$𝐹_{π‘ˆβ’π‘ˆ}$, where $𝐹^{sin \spaceπœ™}_{πΏβ’π‘ˆ}$ 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).

form factors↗
DOE OSTI2025

New Measurements of the Deuteron-to-Proton 𝐹 2 Structure-Function Ratio

Nucleon structure functions, as measured in lepton-nucleon scattering, have historically provided a critical observable in the study of partonic dynamics within the nucleon. However, at very large parton momenta, it is both experimentally and theoretically challenging to extract parton distributions due to the probable onset of nonperturbative contributions and the unavailability of high-precision data at critical kinematics. Extraction of the neutron structure and the d quark distribution have been further challenging because of the necessity of applying nuclear corrections when utilizing scattering data from a deuteron target to extract the free neutron structure. However, a program of experiments has been carried out recently at the energy-upgraded Jefferson Lab electron accelerator aimed at significantly reducing the nuclear correction uncertainties on the d quark distribution function at large partonic momentum. This allows leveraging the vast body of deuterium data covering a large kinematic range to be utilized for d quark parton distribution function extraction. In this Letter, we present new data from experiment E12-10-002, carried out in Jefferson Lab Experimental Hall C, on the deuteron to proton cross section ratio at large Bjorken π‘₯. These results significantly improve the precision of existing data and provide a first look at the expected impact on quark distributions extracted from parton distribution function fits.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Recoil polarization in 𝐾 + β’π‘Œ 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 and 7.546 GeV span the range of four-momentum transfer 𝑄 2 from 0.3 to 4.5GeV 2 and invariant mass π‘Š from 1.6 to 2.4 GeV, while covering the full center-of-mass angular range of the 𝐾 + . These new Ξ› 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 Ξ£ 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 πΎβ’π‘Œ, and for improved insight into the strong interaction in the nonperturbative domain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurement of single- and double-polarization observables in the photoproduction of πœ‹ + β’πœ‹ βˆ’ meson pairs off the proton using CLAS at Jefferson Laboratory

The photoproduction of πœ‹ + β’πœ‹ βˆ’ meson pairs off the proton has been studied in the reaction π›Ύβ’π‘β†’π‘β’πœ‹ + β’πœ‹ βˆ’ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the beam and target asymmetries, 𝐼 𝑠,𝑐 and 𝑃 π‘₯,𝑦 , have been measured along with the beam-target double-polarization observables, 𝑃$^{𝑠,𝑐}_{π‘₯,𝑦}$, using a transversely polarized target with center-of-mass energies ranging from 1.51 GeV up to 2.04 GeV. These data and additional πœ‹β’πœ‹ photoproduction observables from CLAS and experiments elsewhere were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from 𝑠-channel resonance production are observed in addition to 𝑑-channel exchange processes. The data indicate significant contributions from 𝑁* and Ξ”* resonances in the third and fourth resonance regions.

QCD phenomenology↗
DOE OSTI2025

Photoproduction of two charged pions off protons in the resonance region

Photoproduction of charged pions pairs off protons is studied within the invariant masses of the final state hadrons from 1.6 to 2.4 GeV at the Thomas Jefferson National Accelerator Facility with the CLAS detector. The total and differential cross sections and spin-density matrix elements are presented for the isobars pρ 0 (770), Ξ”(1232) ++ Ο€ βˆ’ , and Ξ”(1232) 0 Ο€ + . The data are included in the Bonn-Gatchina coupled-channel analysis and provide the information necessary to determine the branching fractions of Nρ(770) decays for most known N* and Ξ”* resonances. For the first time, the Nρ branching ratios are obtained here from an event-based likelihood to Ξ³p β†’ Ο€ + Ο€ βˆ’ p.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Dihadron azimuthal correlations in deep-inelastic scattering off nuclear targets

We measured the nuclear dependence of the di-pion azimuthal correlation function in deepinelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) and a 5 GeV electron beam. As the nuclear-target size increases, transitioning from deuterium to carbon, iron, and lead, the correlation function broadens monotonically. Its shape exhibits a significant dependence on kinematics, including the transverse momentum of the pions and the difference in their rapidity. None of the various Monte-Carlo event generators we evaluated could fully replicate the observed correlation functions and nuclear effects throughout the entire phase space. As the first study of its kind in DIS experiments, this research provides an important baseline for enhancing our understanding of the interplay between the nuclear medium and the hadronization process in these reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗