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Results for “photon production”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Comparison of photon-photon and photon-magnetic field pair production rates

Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense (10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field (gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

Burns, M. L.↗
DOE OSTI2021

Search for dark photons in Higgs boson production via vector boson fusion in proton-proton collisions at $ \sqrt{s} $ = 13 TeV

A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS collaboration at the LHC, using a data set corresponding to an integrated luminosity of 130 fb$^{−1}$, recorded at a center-of-mass energy of 13 TeV in 2016–2018. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for production via vector boson fusion and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, the observed (expected) 95% confidence level upper limit on the branching fraction is 3.5 (2.8)%. This is the first search for such decays in the vector boson fusion channel. Combination with a previous search for Higgs bosons produced in association with a Z boson results in an observed (expected) upper limit on the branching fraction of 2.9 (2.1)% at 95% confidence level.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1986

Electron-positron pair production by ultrarelativistic electrons in a soft photon field

The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results are obtained for the astrophysically interesting case in which the interaction between an ultrarelativistic electron and a soft photon results in electron-positron pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. It is found that the energy at which the positron distribution peaks is inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semianalytical expressions are obtained for the energy losses of the primary electrons.

Mastichiadis, A.↗
DOE OSTI2024

Gravitational production of completely dark photons with nonminimal couplings to gravity

Dark photons are a theorized massive spin-1 particle which can be produced via various mechanisms, including cosmological gravitational particle production (GPP) in the early universe. In this work, we extend previous results for GPP of dark photons to include nonminimal couplings to gravity. We find that nonminimal couplings can induce a ghost instability or lead to runaway particle production at high momentum and discuss the constraints on the parameter space such that the theory is free of instabilities. Within the instability-free regime we numerically calculate the particle production and find that the inclusion of nonminimal couplings can lead to an enhancement of the particle number. As a result, GPP of nonminimally coupled dark photons can open the parameter space for production of a cosmological relevant relic density (constituting all or part of the dark matter) as compared to the minimally-coupled theory. These results are independent of the choice of inflation model, which we demonstrate by repeating the analysis for a class of rapid-turn multi-field inflation models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2021

On-Orbit Radiometric Performance on ICESat-2

NASA’s ICESat-2 mission measures Earth’s elevation with the Advanced Topographic Laser Altimeter System (ATLAS), a 6-beam photon-counting laser altimeter. The Global Geolocated Photon data product (ATL03) is the primary source of photon information used by surface-type-specific higher-level products, along with the Atmospheric Layer Characteristics product (ATL09). ATL03 provides time-tagged, geolocated photon heights referenced to the ellipsoid and a parameter providing an initial classification of photon events as signal or background. We use this classification to evaluate ATLAS radiometry (number of signal photons per transmitted laser pulse) over short time scales and over the mission to date. The radiometric performance of ATLAS will in part determine what differences in the signal and background photon rates are significant and indicate geophysical, rather than instrumental, changes. We find the ATLAS radiometry is very stable over short time scales and exhibits a long-term decrease of ∼1 signal photon per laser pulse (∼-12%) in the strong spots over the first 1.5 years of the mission.

Aimee Gibbons↗
DOE OSTI2022

Longitudinal double helicity asymmetry $A_{LL}$ from direct photon, jet and charged pion production in polarized $\vec{p}+\vec{p}$ collisions

Understanding the proton spin composition from the quarks and gluons spin polarization and their motion is important to test various kinds of sum rules and nonperturbative properties of hadrons. At the Relativistic Heavy Ion Collider (RHIC), we collide longitudinally polarized proton beams and measure the double helicity asymmetry A_{LL} A L L , which is an important physical quantity for extracting the polarized parton distribution functions (PDFs) of the proton. Direct photon, jet and charged pion production are good channels to probe the gluon spin polarization inside the proton, with the ability to probe also the sign of the gluon spin. Direct photon production is the theoretically ``cleanest’’ channel, with little fragmentation contribution, but limited by statistics. On the other hand, jet and charged pion production have more statistics, but include more hard processes and hadronization effects. I will present the recent measurements of direct photon, jet and charged pion A_{LL} A L L s at PHENIX and show their complementary roles in extracting the gluon spin.

Ji, Zhongling↗
DOE OSTI2026

Rotating synchrotron radiation: Photon emission from magnetized and rotating quark-gluon plasma

This paper investigates the production of nonprompt photons originating from rotating synchrotron radiation (RoSyRa), specifically the emission of photons by a rigidly rotating quark-gluon plasma in thermal equilibrium, in the presence of an external magnetic field. We compute the nonprompt photon spectrum and its elliptic flow (𝑣 2 ) at midrapidity. In particular, we investigate the finite-volume effects. We find that at low transverse momentum, the magnetic field induces a significant 𝑣 2 , while the plasma rotation boosts the synchrotron radiation of negatively charged quarks. These findings make RoSyRa a viable candidate mechanism to resolve the “direct photon puzzle.”

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Heralded Generation of Correlated Photon Pairs from CdS/CdSe/CdS Quantum Shells

Quantum information processing demands efficient quantum light sources (QLS) capable of producing high-fidelity single photons or entangled photon pairs. Single epitaxial quantum dots (QDs) have long been proven to be efficient sources of deterministic single photons; however, their production via molecular-beam epitaxy presents scalability challenges. Conversely, colloidal semiconductor QDs offer scalable solution processing and tunable photoluminescence, but suffer from broader linewidths and unstable emissions. This leads to spectrally inseparable emission from exciton (X) and biexciton (XX) states, complicating the production of single photons and triggered photon pairs. Here, in this work, we demonstrate that colloidal semiconductor quantum shells (QSs) achieve significant spectral separation (∼75–80 meV) and long temporal stability of X and XX emissive states, enabling the observation of exciton-biexciton bunching in colloidal QDs. Our low-temperature single-particle measurements show cascaded XX-X emission of single photon pairs for over 200 s, with minimal overlap between X and XX features. The X-XX distinguishability allows for an in-depth theoretical characterization of cross-correlation strength, placing it in perspective with photon pairs of epitaxial counterparts. These findings highlight a strong potential of semiconductor quantum shells for applications in quantum information processing.

biexciton↗
DOE OSTI2020

First Measurement of Λ c Baryon Production in Au + Au Collisions at s N N = 200 GeV

Herein we report on the first measurement of the charmed baryon Λ c ± production at midrapidity ( | y | < 1 ) in Au + Au collisions at s NN = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The Λ c / D 0 [denoting ( Λ c + + Λ c - ) / ( D 0 + D ¯ 0 ) ] yield ratio is measured to be 1.08 ± 0.16 ( stat ) ± 0.26 ( sys ) in the 0%–20% most central Au + Au collisions for the transverse momentum ( p T ) range 3 < p T < 6 GeV / c . This is significantly larger than the pythia model calculations for p + p collisions. The measured Λ c / D 0 ratio, as a function of p T and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au + Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured Λ c / D 0 ratio.

13000 GeV-cms/nucleon↗
NASA NTRS1983

Active galaxies and the diffuse Gamma-Ray background

A model for the origin of relativistic particles and gamma rays in active galactic nuclei and quasars, together with recent HEAO-1 observations of the spectra of active galaxies from 2 to 165 keV, provide the basis for a reexamination of the nature of the extragalactic gamma ray background. Active galaxies account for the observed background if their X-ray spectra steepen to E.021 above 100 keV, as observed in Cen-A, together with a further steepening to E.021 as a result of absorption of gamma rays by photon-photon pair production interactions with X-ray photons. The compactness of active galaxies required to give this steepening is consistent with estimates of their typical luminosity and radius.

Kazanas, D.↗
NASA NTRS1983

Galactic absorption of high-energy gamma-rays from Cygnus X-3

The importance of cosmic blackbody photons as an absorbing gas for the attenuation of high-energy photons via pair production in photon-photon collision is examined for the specific case of gamma rays from Cyg X-3. Recent observational results on this photon flux in the range from 2 x 10 to the 15th to 2 x 10 to the 16th eV are corrected for this attenuation. The absorption optical depth to the source is about unity, and the corrected flux is about a factor of three higher; as a result, it does not extrapolate from the data at lower energies (10 to the 12th eV).

Gould, R. J.↗
NASA NTRS2002

Regimes of Pulsar Pair Formation and Particle Energetics

We investigate the conditions required for the production of electron-positron pairs above a pulsar polar cap (PC) and the influence of pair production on the energetics of the primary particle acceleration. Assuming space-charge limited flow acceleration including the inertial frame-dragging effect, we allow both one-photon and two-photon pair production by either curvature radiation (CR) photons or photons resulting from inverse-Compton scattering of thermal photons from the PC by primary electrons. We find that,, while only the younger pulsars can produce pairs through CR, nearly all known radio pulsars are capable of producing pairs through non-resonant inverse-Compton scatterings. The effect of the neutron star equations of state on the pair death lines is explored. We show that pair production is facilitated in more compact stars and more a massive stars. Therefore accretion of mass by pulsars in binary systems may allow pair production in most of the millisecond purser population. We also find that two-photon pair production may be important in millisecond pursers if their surface temperatures are above approx. or equal to three million degrees K. Pursers that produce pairs through CRT wilt have their primary acceleration limited by the effect of screening of the electric field. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sup 1/2, sub rot) dependence. The acceleration voltage drop in pursers that produce pairs only through inverse-Compton emission will not be limited by electric field screening. In this regime, the high-energy luminosity should follow a L(sub HE) proportional to dot-E(sub rot) dependence. Thus, older pursers will have significantly lower gamma-ray luminosity.

Harding, Alice K.↗
DOE OSTI2021

An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab

Positron beams, both polarized and unpolarized, are identified as important ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors of the energy-momentum tensor. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector

This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb -1 of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688±23(stat) $^{+75}_{-71}$(syst) fb, to be compared with the standard model prediction of 515$^{+36}_{-42}$ fb at next-to-leading order in QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

A measurement of the charge asymmetry in top-quark pair ($t\bar{t}$) production in association with a photon is presented. The measurement is performed in the single-lepton $t\bar{t}$ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb –1 . The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be A C =–0.003 ± 0.029 in agreement with the Standard Model expectation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1992

Radiation transfer in gamma-ray bursts

We have calculated gamma-ray radiative transport in regions of high-energy density, such as gamma-ray burst source regions, using a discrete ordinate, discrete energy group method. The calculations include two-photon pair production and annihilation, as well as three-photon annihilation. The radiation fields itself acts as an absorbing medium, and the optical depth depends on its intensity, so the problem is intrinsically nonlinear. Spherical divergence produces effective collimation of the flux. At high optical depth the high energy (E is greater than 1 MeV) portion of the emergent spectrum assumes a nearly universal form. An approximate limit is derived for the high-energy flux from a gamma-ray burst source region of given size, and the implications of this limit for the distance to the 1979 March 5 event are briefly discussed. We discuss more generally the problem of very luminous bursts, and implications of Galactic halo distances for flare models.

Carrigan, B. J.↗
DOE OSTI2020

Photon induced $K\Lambda $ production on the proton at $E_{\gamma} < 3$ GeV

The associated photoproduction of $K\Lambda$ from the proton for $E_{\gamma} < 3$ GeV is studied using an isobar model in which the non-resonant contributions corresponding to $s$, $t$, $u$ channel diagrams are obtained from a non-linear sigma model with chiral SU(3) symmetry. The model also predicts a contact term and its coupling strength in a natural way to preserve gauge symmetry. The parameters used are the pion decay constant $f_{\pi}$, vector and axial vector current couplings of the baryon octet in terms of the symmetric and antisymmetric couplings $D$ and $F$. In the non-resonant sector, the model is almost parameter free except a common cut-off parameter $\Lambda_{B}$, to describe the hadronic form factors at the strong kaon-nucleon-hyperon($KN\Lambda$) vertices. In the resonance sector, contribution from the various nucleon resonances($R$) in the $s$ channel, hyperon resonances($Y^{*}$) in the $u$ channel, and the kaon resonances($K^{*}$ and $K_{1}$) in the $t$ channel, which are present in the PDG having spin $\le \frac{3}{2}$ and mass $<2$ GeV with significant branching ratio in $K\Lambda$ decay mode have been considered. In the case of the nucleon resonances($R$), the couplings $\gamma NR$ at the electromagnetic vertices are determined in terms of the helicity amplitudes and the $RK\Lambda$ couplings at the strong vertices are determined by the partial decay width of the resonances($R$) decaying to $K\Lambda$. The strong and the electromagnetic couplings of $u$ and $t$ channel resonances are fitted to reproduce the experimental data of CLAS and SAPHIR. The numerical results are presented for the total and differential scattering cross sections and are compared with the available experimental data from CLAS and SAPHIR as well as with some of the recent theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗