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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
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DOE OSTI2023

First Measurement of Λ Electroproduction off Nuclei in the Current and Target Fragmentation Regions

Here, we report results of Λ hyperon production in semi-inclusive deep-inelastic scattering off deuterium, carbon, iron, and lead targets obtained with the CLAS detector and the Continuous Electron Beam Accelerator Facility 5.014 GeV electron beam. These results represent the first measurements of the Λ multiplicity ratio and transverse momentum broadening as a function of the energy fraction (z) in the current and target fragmentation regions. The multiplicity ratio exhibits a strong suppression at high z and an enhancement at low z. The measured transverse momentum broadening is an order of magnitude greater than that seen for light mesons. This indicates that the propagating entity interacts very strongly with the nuclear medium, which suggests that propagation of diquark configurations in the nuclear medium takes place at least part of the time, even at high z. The trends of these results are qualitatively described by the Giessen Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity ratios. These observations will potentially open a new era of studies of the structure of the nucleon as well as of strange baryons.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

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 Roper and collaborators in analyses of πN hadroproduction data, has 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 electro production 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 emerge.

Mokeev, Victor I. [Thomas Jefferson National Accel↗
DOE OSTI2022

First Measurement of $\Lambda$ Electroproduction off Nuclei in the Current and Target Fragmentation Regions

We report results of $\Lambda$ hyperon production in semi-inclusive deep-inelastic scattering off deuterium, carbon, iron, and lead targets obtained with the CLAS detector and the CEBAF 5.014 GeV electron beam. These results represent the first measurements of the $\Lambda$ multiplicity ratio and transverse momentum broadening as a function of the energy fraction ($z$) in the current and target fragmentation regions. The multiplicity ratio exhibits a strong suppression at high $z$ and an enhancement at low $z$. The measured transverse momentum broadening is an order of magnitude greater than that seen for light mesons. This indicates that the propagating entity interacts very strongly with the nuclear medium, which suggests that propagation of di-quark configurations in the nuclear medium takes place at least part of the time, even at high $z$. The trends of these results are qualitatively described by the GiBUU transport model, particularly for the multiplicity ratios. These observations will potentially open a new era of studies of the structure of the nucleon as well as of strange baryons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the Deeply Virtual Neutral Pion Electroproduction Cross Section off the Proton at 10.6 GeV using the CLAS12 Detector

Deeply virtual exclusive reactions provide unique channels to study both transverse and longitudinal properties of the nucleon simultaneously, allowing for a 3D image of nucleon substructure. This presentation will discuss work towards extracting an absolute cross section for one such exclusive process, deeply virtual neutral pion production, using 10.6 GeV electron scattering data off a proton target from the CLAS12 experiment in Jefferson Lab Hall B. This measurement is important as exclusive meson production has unique access to the chiral odd Generalized Parton Distributions, and is also a background for other exclusive processes such as Deeply Virtual Compton Scattering, making the determination of this cross section crucial for other exclusive analyses.

Johnston, Robert↗
DOE OSTI2024

A study of charge symmetry violation in fragmentation functions extracted from semi-inclusive electroproduction of charged pions from protons and deuterons

We have measured the flavor dependence of multiplicities for ?+ and ?? production in semi- inclusive deep-inelastic scattering (SIDIS) on proton and deuteron targets. We used a 10.6 GeV electron beam at Jefferson Lab, and 4 msr solid angle spectrometers (HMS for electrons, SHMS for pions), the lepton vertex spanned the kinematic range 0.3 < ? < 0.6, 2 < ?2 < 5 GeV2, and 4 < ?2 < 11 GeV2. The pion fractional momentum range was 0.3 < ? < 0.7 and the small transverse momentum range was 0 < ?? < 0.25 GeV. We used the multiplicities to form sum-and- difference ratios, testing the validity of factorization. We extracted two favored and two unfavored flavor-dependent fragmentation functions (FFs) using these multiplicities. Assuming factorization at low ?? , we find that these two FFs allow for isospin breaking (charge symmetry violation) at low ?, while converging to a common flavor independent value at the highest ? of this experiment, where the factorization is most applicable.

Bhatt, Hem↗
DOE OSTI2025

Exploring the Nucleon Structure via Deep Electroproduction Processes

Understanding the internal structure of the nucleon is a fundamental goal of modern physics, which aims at a comprehensive framework describing the internal dynamics of quarks and gluons. Among other structure functions, Generalized Parton Distributions (GPDs) offer a powerful framework for describing the nucleon dynamics by correlating the longitudinal momentum and the transverse position of its internal partons. Such a correlation provides a three-dimensional picture of the nucleon and enables access to fundamental properties, including the internal pressure distributions and the parton’s angular momentum contribution to the nucleon's total spin, thereby playing a central role in resolving the nucleon spin puzzle. At the Thomas Jefferson National Facility (JLab), polarized electron beam experiments allow for probing GPDs through the measurement of hard exclusive processes. Among the cleanest experimental channels, we find the electro-production of a real photon through the Deeply Virtual Compton Scattering (DVCS) mechanism. The first data-taking period of the CLAS12 program, taking place in 2018, allowed for unique DVCS Beam Spin Asymmetry (BSA) measurements in the phase space covered by a 10.6 GeV polarized electron beam impinging on an unpolarized liquid hydrogen target. Although detecting all final-state particles ensures exclusivity of the process, conservation laws indicate that it is not mandatory. I adopt an approach omitting the direct detection of the recoil proton, providing a simplified yet effective event selection strategy that boosts statistics and gives access to a larger phase space sensitive to the underlying GPD dynamics through BSA and cross section measurements. The Double DVCS (DDVCS) process promises a dedicated mapping of GPDs. Contributing to the electro-production of a lepton pair cross-section, the DDVCS reaction extends DVCS by allowing the final-state photon to be virtual, enriching the kinematic phase space and providing unique access to the internal correlations encoded by GPDs. A feasibility study is conducted to assess the potential of future DDVCS measurements at Jefferson Lab and the future Electron-Ion Collider (EIC). While Jefferson Lab will provide DDVCS measurements in the valence region through the SoLID$\mu$ and $\mu$CLAS12 experimental projects, in the long term, the EIC will provide complementary measurements in the sea region, both accessing unprecedented information about GPDs in a phase space region otherwise inaccessible. Taken together, these investigations demonstrate both the current capabilities and future opportunities for probing GPDs through exclusive processes. The experimental analysis of DVCS at CLAS12 provides precise measurements within an established framework, while the phenomenological study of DDVCS opens the door to richer and more comprehensive explorations with future detectors and facilities.

Alvarado, Juan [Université Paris-Saclay: Gif-sur-Y↗
DOE OSTI2022

Search For Excited Cascade Hypersons (¿*-) Using the CLAS12 Spectrometer at Jefferson Laboratory

The number of experimentally observed doubly strange Cascade states to date is far fewer than has been predicted theoretically. The CLAS12 Very Strange physics program (E12- 11-005A) at the Thomas Jefferson National Accelerator Facility aims to study the electroproduction of these states using the newly upgraded CEBAF Large Acceptance Spectrometer for 12 GeV (CLAS12) in experimental Hall B. In this project, the reaction ep ! e0K+K+??? ! e0K+K+K?(?=?0) is studied using CLAS12 Run Group A (RG-A) data sets taken by impinging electron beams of 10:2 and 10:6 GeV energies on an LH2 target. Scattered electrons are detected with either the Forward Detector (FD), covering a polar angle range of 5? to 35? to study electroproduction, or with the Forward Tagger (FT), covering a polar angle range of 2:5? to 4:5?, to study quasi-real photoproduction. The CLAS12 detector with nearly a 4? solid angle coverage is used to detect scattered electrons and charged kaons in the ?final state. ?=?0 hyperons are reconstructed using the missing mass technique to explore intermediate doubly-strange hyperons (???) that decay to K? and ?=?0. No statistically significant ??? states other than the ???(1530) were found in the missing mass spectra based on the currently available statistics in the CLAS12-FD acceptance only. A maximum log-likelihood method is implemented to determine the statistical significance and the upper limits on the ???(1820) electroproduction cross section by constructing 95% confidence level boundaries on the ???(1820) yields. Additional research was conducted to investigate the upper limit electroproduction cross section of the reaction ep ! e0K+K+??? ! e0K+K+K?(?=?0) as a function of the electroproduced ??? mass and the differential cross section ( d?dMM(e0K+K+) ) as a function of missing mass MM(e0K+K+) for electroproduction and quasi-real photoproduction processes.

Khanal, Achyut↗
DOE OSTI2020

Excited nucleon spectrum and structure studies with CLAS and CLAS12

The study of the spectrum and structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The CLAS detector in Hall B has provided the dominant part of the available world data on most relevant meson electroproduction channels off the nucleon in the resonance region for Q2 up to 5 GeV2. Analyses of CLAS data for the exclusive channels πN, ηN, and π+π-p on a proton target have provided the only results available on the Q2 evolution of the electro-excitation amplitudes for the transitions from the initial photon-proton to the final N* states in the mass range up to W =1.8 GeV. These electrocouplings allow for exploration of the internal structure of the produced excited nucleon states. This work has made it clear that consistent results from independent analyses of several exclusive channels with different resonance hadronic decay parameters and non-resonant backgrounds but the same N* electro-excitation amplitudes, is essential to have confidence in the extracted results. Starting in early 2018, a program to study the spectrum and structure of N* states in various exclusive electroproduction channels using the new CLAS12 spectrometer commenced. These studies will probe the structure of N* states in the mass range up to W =3 GeV and for Q2 as low as 0.05 GeV2 and as high as 10-12 GeV2, thus providing a means to access N* structure information spanning a broad range of distance scales. Quasi-real photoproduction studies are also planned to search for additional N* states, the so-called hybrid baryons, for which the glue serves as an active structural component. In this talk the N* programs from both CLAS and CLAS12 will be reviewed.

Carman, D. S.↗
DOE OSTI2024

Determination of Pion and Kaon Structure Using the Sullivan Process at Moderate to large Fractional Momentum

Significant progress has been made in describing the structure of hadrons in terms of Quantum ChromoDynamics (QCD) degrees of freedom. The recently developed framework of Generalized Parton Distribtions (GPDs) may provide the path towards three-dimensional imaging of the hadronic structure. Integrating the GPDs over the fractional momentum (x), the form factors are obtained which are integrally related to understanding the emergent hadron mass-generating mechanism (EHM) embedded in QCD and the mass-scale that characterizes the proton [Roberts (2016)]. The Sullivan process, in which one scatters electrons off the proton?s virtual meson cloud and thus creates a meson target, is used to probe this structure. Studies of kaon electroproduction offer unique opportunities in this. The last two decades saw a dramatic improvement in the precision of charged meson form factor data, and new results have become available on the transition form factor. The KaonLT experiment (E12-09-011) carried out in Hall C at Jefferson Lab (Jlab) was designed to measure longitudinal/transverse (L/T) separated kaon cross sections required to access form factors and GPDs [Bosted et al. (2008)]. KaonLT aimed to confirm the exclusive kaon electroproduction mechanism, which is essential for determining the kaon form factor and investigating GPDs. The results obtained from this experiment have provided the highest Q2 for L-T separated kaon electroproduction cross section, and it is the first time that a separated kaon cross-section measurement has been carried out above W = 2:2GeV.

Trotta, Richard↗
DOE OSTI2022

New baryon states in exclusive meson photo-/electroproduction with CLAS

Impressive progress achieved in the past decade in experimental studies of exclusive meson photoproduction off protons and global multichannel amplitude analyses has resulted in the discovery of several long-awaited new nucleon resonances, with a decisive impact from the results of KΛ and KΣ photoproduction measured with the CLAS detector at Jefferson Lab. Further extension of these efforts towards combined studies of exclusive meson photo- and electroproduction data off protons will be presented. A new excited state of the nucleon, the N 0 (1720)3/2 +, discovered from combined analyses of π +π -p photo- and electroproduction data, in addition to new resonances discovered in photo- and hadroproduction data, demonstrate the promising prospects of this new research avenue for the discovery of additional new resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Electromagnetic production of kaons on the nucleon

Studies of the electromagnetic production of strange quarks started in the 1950s as something of a curiosity that puzzled experimentalists and theorists alike. Eventually, a nascent understanding of these processes began to take shape through the first pioneering experiments dedicated to explore photo- and electroproduction that were carried out in the period from the 1950s to the 1980s. As the datasets increased, concomitant advances in theoretical models were realized. However, these initial studies also made clear that more precise data was essential to continue to move forward. A paradigm shift occurred in the 1990s with the development of second-generation facilities at ELSA, MAMI, SPring-8, and JLab. High-intensity, high duty-factor accelerators, coupled with novel detector systems and advances in computing and readout electronics, brought nuclear physics experiments forward by orders of magnitude in counting statistics compared to the first-generation efforts. This was an utter boon to strangeness physics investigations, and to date, more than 50 dedicated experiments in kaon photo- and electroproduction have been completed at facilities around the world, leading to a host of experimental observables that have enabled significant advances in the exploration of strongly interacting systems that decay via $s\bar{s}$ quark pair creation. These data have proven to be an essential complementary pathway to study the spectrum and structure of the excited states of the nucleon, and the search for missing and exotic baryon configurations. As well, investigations in these channels are requisite for exploring hypernuclear production as a probe of the $YN$ interaction and for studies of the electromagnetic form factors of strange mesons. This review was designed to provide the first-ever in-depth overview of both the experimental and theoretical progress in the field of the electromagnetic production of strangeness. This work looks back over 70 years of past developments, discusses ongoing work and near-term plans, and details future possibilities being considered for third-generation facilities. Extensive lists of the available datasets and theoretical models are provided, together with a comprehensive supporting bibliography of the field. Throughout this work, the primary impacts of these explorations are highlighted, along with connections to a wide range of related phenomenological applications. An important goal of this review is to provide a complete, (reasonably) self-contained guide into this field prepared at a level that is relevant for both new and seasoned scientists, whether experimentalists, phenomenologists, or theorists, to better understand what has been accomplished by so many dedicated folks-each building on what has come before-and to appreciate the exciting future potential for continued studies in this area.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Photo- and Electrocouplings of Nucleon Resonances

Advances in the exploration of the spectrum and structure of the excited states of the nucleon from experiments with electromagnetic probes on proton targets are presented here. Impressive progress has been achieved in the studies of exclusive meson photoproduction in experiments with continuous electron beams and with detectors of almost 4π acceptance. The high-quality data, coupled with the advances in the amplitude analyses of exclusive photo- and hadroproduction data, allow for the observation of several long-awaited new baryon states known previously as the “missing” resonances. Studies of exclusive meson electroproduction in the resonance region with the CLAS detector at JLab have provided the dominant part of the available world information on exclusive meson electroproduction observables. These data offer unique information on the structure of most well-established excited nucleon states in the mass region up to 1.8 GeV in terms of the evolution of their electroexcitation amplitudes with momentum transfer of the virtual photon. We discuss the impact of these results on the insight into the strong interaction dynamics that underlie the generation of the full spectrum of nucleon resonances of distinctively different structure. These results shed light on the emergence of hadron mass, which is one of the most important and still open problems in the Standard Model. The extension of the nucleon resonance stud

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗