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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Charged-particle multiplicity distributions over a wide pseudorapidity range in p–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

This paper presents the primary charged-particle multiplicity distributions in proton–lead collisions at a centre-of-mass energy per nucleon–nucleon collision of $\sqrt{s_{NN}}$ = 5.02 TeV. The distributions are reported for non-single diffractive collisions in different pseudorapidity ranges. The measurements are performed using the combined information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE. The multiplicity distributions are parametrised with a double negative binomial distribution function which provides satisfactory descriptions of the distributions for all the studied pseudorapidity intervals. The data are compared to models and analyzed quantitatively, evaluating the first four moments (mean, standard deviation, skewness, and kurtosis). The shape evolution of the measured multiplicity distributions is studied in terms of KNO variables and it is found that none of the considered models reproduces the measurements. This paper also reports on the average charged-particle multiplicity, normalised by the average number of participating nucleon pairs, as a function of the collision energy. The multiplicity results are then compared to measurements made in proton–proton and nucleus–nucleus collisions across a wide range of collision energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

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

Measuring deeply virtual Compton scattering (DVCS) 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 Compton form factors H and E . Published by the American Physical Society 2024

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
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 𝑥. 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↗
NASA NTRS1979

Gamma-ray evidence for a galactic halo

Gamma-ray evidence for the existence of a cosmic-ray halo around the Galaxy is examined. Gamma-ray data obtained by SAS-2 and COS-B and nonthermal radio continuum data are shown to indicate the nonconfinement of cosmic rays to the spiral arms and thus the existence of a larger propagation disk through which cosmic rays diffuse. The latitudinal distribution of gamma rays observed by SAS-2 is found to be consistent with the existence of a thin disk-shaped electron halo of half-thickness 1.5 kpc. The propagation of nucleons is determined indirectly from their radial distribution in the galactic plane, which is obtained from an analysis of the longitudinal distribution of gamma rays in the plane. The resulting distributions are found to be similar to the distribution of supernovae in the Galaxy, implying a galactic origin for cosmic rays and a half-thickness of less than 3 kpc.

Stecker, F. W.↗
NASA NTRS1987

Cosmic-ray propagation in the Galaxy and in the heliosphere - The path-length distribution at low energy

The energy dependence of the path-length distribution of cosmic rays at low energies, below relativistic velocities, is studied, and its implications for models of cosmic-ray confinement and propagation in the Galaxy and Galactic halo, including the effects of a possible Galactic wind, are studied. It is found that the mean free path in Galactic propagation must be fully energy-dependent, with the mean of an exponential path-length distribution increasing with increasing energy below 1 GeV per nucleon and decreasing with increasing energy above 1 GeV per nucleon. This indicates that, at low energies, diffusion is not the controlling process. The path-length distribution is not purely exponential but is depleted in short path lengths at low energies. This depletion is energy-dependent, being largest at low energies and decreasing with increasing energy.

Garcia-Munoz, M.↗
DOE OSTI2026

Next-to-next-to-leading power corrections to unpolarized Semi-Inclusive Deep Inelastic Scattering

Semi-Inclusive Deep Inelastic Scattering (SIDIS) is a key tool for exploring the three-dimensional structure of the nucleon through Transverse Momentum Dependent parton distributions and fragmentation functions. While leading-power contributions to the SIDIS cross-section are well established, next-to-leading power (NLP) corrections of order 1/Q and next-to-next-to-leading power (NNLP) corrections of order 1/Q 2 to the hadronic tensor have only recently begun to be systematically investigated. These corrections are essential for reliable phenomenology and interpretation of modern high-precision data. In recent papers by one of the authors, NNLP corrections to the Drell-Yan process were derived using the rapidity factorization formalism. In the present work, we extend this approach to SIDIS and obtain analytic expressions for the unpolarized structure functions. We derive NNLP corrections that include convolutions of unpolarized distributions, f 1 , with unpolarized fragmentation functions, D 1 , and Boer-Mulders functions, ${h}_1^{\perp }$, with Collins fragmentation functions, ${H}_1^{\perp }$. We compare our results with previous formulations, provide numerical studies, confront our predictions with HERMES and COMPASS measurements, and present predictions for future experiments at Jefferson Lab and the Electron-Ion Collider.

deep inelastic scattering↗
NASA NTRS1982

Fluid dynamical description of relativistic nuclear collisions

On the basis of both a conventional relativistic nuclear fluid dynamic model and a two fluid generalization that takes into account the interpenetration of the target and projectile upon contact, collisions between heavy nuclei moving at relativistic speeds are calculated. This is done by solving the relevant equations of motion numerically in three spatial dimensions by use of particle in cell finite difference computing techniques. The effect of incorporating a density isomer, or quasistable state, in the nuclear equation of state at three times normal nuclear density, and the effect of doubling the nuclear compressibility coefficient are studied. For the reaction 20Ne + 238U at a laboratory bombarding energy per nucleon of 393 MeV, the calculated distributions in energy and angle of outgoing charged particles are compared with recent experimental data both integrated over all impact parameters and for nearly central collisions.

Nix, J. R.↗
NASA NTRS1985

The effect of the relative nuclear size on the nucleus-nucleus interactions

The experimental data on the interactions of light nuclei (d, He(4), C(12)) at the momentum 4.2 GeV/cA with the carbon nuclei were taken in the 2-m propane bubble chamber. The distributions in the number of interacting nucleons, the spectra of protons, the mean energies of secondary pions and protons, the mean fractions of energy transferred to the pion and nucleon components are presented. The results of the investigation of the mechanism of nucleus-nucleus interactions can be used to calculate the nuclear cascades in the atmosphere.

Erofeeva, I. N.↗
NASA NTRS1977

Gamma rays and large scale galactic structure

Gamma ray astronomy is now beginning to provide a new look at the galactic structure and the distribution of cosmic rays, both electrons and nucleons, within the galaxy. The observations are consistent with a galactic spiral-arm model in which the cosmic rays are linearly coupled to the interstellar gas on the scale of the spiral arms. The agreement between the predictions of the model and the observations for regions of the plane where both 21-cm and 2.6-mm CO surveys exist emphasizes the need to extend these observations to include the entire plane. Future gamma-ray observations with more sensitivity and better angular resolutions, combined with these radio surveys, should shed new light on the distribution of cosmic rays, the nature of the galaxy, and the location and intensity of the spiral arms.

Kniffen, D. A.↗
DOE OSTI2024

N* Physics with CLAS12 at Jefferson Lab

Nucleons are the most fundamental bound three-body systems in Nature. With the CLAS12 spectrometer at Jefferson Lab, the spectrum and the structure of nucleon resonances is explored. This includes studies of exclusive piN, pi+pi-p, KLambda, and KSigma electroproduction reactions and the evolution of the electrocouplings of resonances with photon virtuality Q^2. Such type of studies with CLAS have revealed a complex interplay between a core of dressed quarks and an external meson-baryon cloud inside of the excited nucleon states. With CLAS12, also measurements of N -> N* transitions in the DIS region have been performed, addressing the three-dimensional structure of nucleon resonances through their transition GPDs (generalized parton distributions). In the future, the increase of the CEBAF energy and the upgrade of the CLAS12 spectrometer to study exclusive electroproduction channels at higher luminosities and photon virtualities will offer a unique opportunity to study the nucleon excitation mechanisms.

Achenbach, Patrick↗
NASA NTRS1972

Primary and secondary particle contributions to the depth dose distribution in a phantom shielded from solar flare and Van Allen protons

Calculations have been made using the nucleon-meson transport code NMTC to estimate the absorbed dose and dose equivalent distributions in astronauts inside space vehicles bombarded by solar flare and Van Allen protons. A spherical shell shield of specific radius and thickness with a 30-cm-diam. tissue ball at the geometric center was used to simulate the spacecraft-astronaut configuration. The absorbed dose and the dose equivalent from primary protons, secondary protons, heavy nuclei, charged pions, muons, photons, and positrons and electrons are given as a function of depth in the tissue phantom. Results are given for solar flare protons with a characteristic rigidity of 100 MV and for Van Allen protons in a 240-nautical-mile circular orbit at 30 degree inclination angle incident on both 20-g/sq cm-thick aluminum and polyethylene spherical shell shields.

Santoro, R. T.↗
DOE OSTI2024

Nucleon tomography and total angular momentum of valence quarks from synergy between lattice QCD and elastic scattering data

We present an exploratory work on integrating lattice-QCD results with experimental data for elastic scattering. Within the framework of generalized parton distributions, this approach allows for the extraction of detailed information about nucleon tomography and the total angular momentum carried by valence quarks. To accomplish this reliably, we introduce a new quantity, the “double ratio,” which significantly reduces the systematic uncertainties inherent in lattice QCD computations. Moreover, we introduce a “shadow” term in the extraction procedure, which is sensitive only to lattice-QCD results. This term allows us to investigate the model dependence of the extraction, providing a more flexible description of the nucleon that goes beyond the previously considered bell-shaped distribution.

Lattice QCD↗
DOE OSTI2025

Measurement of isolated prompt photon production in pp and p–Pb collisions at the LHC

This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p–Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p–Pb collisions at centre-of-mass energies per nucleon pair of $\sqrt{s_{NN}}$ = 5.02 Te and 8.16 TeV, as well as in pp collisions at $\sqrt{s}$ = 5.02 TeV and 8 TeV. The cross section is obtained at midrapidity (|γ| < 0.7) using a charged-track based isolation momentum p$^{iso,~ch}_{T}$ < 1.5 GeV/c in a cone with radius R = 0.4. The data for both collision systems are well reproduced by perturbative QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor R pA for both collision energies is consistent with unity for p T > 20 GeV/c. However, deviations from unity (R pA < 1) of up to 20% are observed for p T < 20 GeV/c with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Nucleon structure studies: DVCS on polarised protons with the CLAS12 experiment, and development of Micromegas detectors for EIC

The quark and gluon structure of nucleons is crucial for understanding the origin of their mass and spin. This information is encoded in structure function such as Generalised Parton Distributions (GPDs), which provide a three-dimensional picture of the nucleon in terms of its constituents. Deeply Virtual Compton Scattering (DVCS) offers the most direct access to GPDs, but their extraction requires high-precision measurements of multiple observables over a wide kinematic range. In 2022 and 2023 the CLAS12 experiment at Jefferson Lab (JLab) collected data from polarised electron scattering on a longitudinally polarised proton target, enabling the first measurement of polarised DVCS asymmetries at JLab 12GeV kinematics. This thesis will present preliminary measurement of the beam, target and double spin DVCS asymmetries from the CLAS12 polarised proton target data. Nucleon structure studies will also constitute a major part of the physics program at the future Electron Ion Collider (EIC). The development of the first detector at the EIC is ongoing and it requires light Micro-Pattern Gaseous Detectors (MPGDs) for its tracking system. This thesis further reports initial tests of Micromegas MPGDs with a two-dimensional readout developed for EIC.

Polcher, Samy [Univ. Paris-Saclay, Gif-sur-Yvette ↗
DOE OSTI2024

New Data-Driven Constraints on the Sign of Gluon Polarization in the Proton

Recently, the possible existence of negative gluon helicity Δ g has been observed to be compatible with existing empirical constraints, including from jet production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider, and lattice QCD data on polarized gluon Ioffe time distributions. We perform a new global analysis of polarized parton distributions in the proton with new constraints from the high- x region of deep-inelastic scattering (DIS). A dramatic reduction in the quality of the fit for the negative Δ g replicas compared to those with positive Δ g suggests that the negative Δ g solution cannot simultaneously account for high- x polarized DIS data along with lattice and polarized jet data. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1984

Survey of He(+)/He(2+) abundance ratios in energetic particle events

First results of a systematic study of the helium ionic charge distribution in the energy range 0.4-0.62 MeV per nucleon in energetic particle events are reported. Large fluctuations of the He(+)/He(2+) ratios are found, especially at low interplanetary particle fluxes. The ratios exceeded a value of 0.3 for 41 days and a value of 1.0 for 11 days out of the 216 days analyzed. The median of the distribution is He(+)/He(2+) = 0.11. No obvious association with optical flare events could be observed for the events richest in He(+). No significant differences were found between the proton energy spectra and the elemental abundances of helium relative to hydrogen and heavy ions for He(+)-rich events versus events low in He(+). However, it has been found that generally He(+)-rich events are predominantly low in energetic particle intensity.

Hovestadt, D.↗