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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Centrality dependence of high-pT D meson suppression in Pb-Pb collisions at $ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=2.76 $ TeV

We measured the nuclear modification factor, R-AA, of the prompt charmed mesons D°, D + and D *+ , and their antiparticles, using the ALICE detector in Pb-Pb collisions at a centre-of-mass energy √s NN = 2.76 TeV in two transverse momentum intervals, 5 < p T < 8 GeV/c and 8 < p T < 16 GeV/c, and in six collision centrality classes. Furthermore, the R AA shows a maximum suppression of a factor of 5-6 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. Finally, a comparison with the R AA of non-prompt J/Ψ from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

From quarks to nucleons in dark matter direct detection

We provide expressions for the nonperturbative matching of the effective field theory describing dark matter interactions with quarks and gluons to the effective theory of nonrelativistic dark matter interacting with nonrelativistic nucleons. We give expressions of leading and subleading order in chiral counting. In general, a single partonic operator matches onto several nonrelativistic operators already at leading order in chiral counting. Keeping only one operator at the time in the nonrelativistic effective theory thus does not properly describe the scattering in direct detection. The matching of the axial-axial partonic level operator, as well as the matching of the operators coupling DM to the QCD anomaly term, include naively momentum suppressed terms. Furthermore, these are still of leading chiral order due to pion poles and can be numerically important.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Radiation of scalar modes and the classical double copy

The double copy procedure relates gauge and gravity theories through color-kinematics replacements, and holds for both scattering amplitudes and in classical contexts. Moreover, it has been shown that there is a web of theories whose scattering amplitudes are related through operations that exchange color and kinematic factors. In this paper, we generalize and extend this procedure by showing that the classical perturbative double copy of pions corresponds to special Galileons. We consider point-particles coupled to the relevant scalar fields, and find the leading and next to leading order radiation amplitudes. By considering couplings motivated by those that would arise from extracting the longitudinal modes of the gauge and gravity theories, we are able to map the non-linear sigma model radiation to that of the special Galileon. We also construct the single copy by mapping the bi-adjoint scalar radiation to the non-linear sigma model radiation through generalized color-kinematics replacements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Search for decays of the 125 GeV Higgs boson into a Z boson and a $\rho$ or $\phi$ meson

Decays of the 125 GeV Higgs boson into a Z boson and a ρ$^{0}$(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $ \sqrt{s} $ = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb$^{−1}$. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Updated search for $ {B}_c^{+} $ decays to two charm mesons

A data set corresponding to an integrated luminosity of 9 fb -1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for B c + → D s &lowast; + — D &lowast; 0 decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to B + decays to final states with similar topologies, are obtained for sixteen $ {B}_c^{+} $ decay modes. For the decay $ {B}_c^{+}\to {D}_s^{+}{\overline{D}}^0 $, an excess with a significance of 3.4 standard deviations is found.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

The Light-Front Schrödinger Equation and Determination of the Perturbative QCD Scale from Color Confinement

The valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a relativistic equation of motion with an effective confining potential U which systematically incorporates the effects of higher quark and gluon Fock states. If one requires that the effective action which underlies the QCD Lagrangian remains conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to light front Hamiltonian theory, the potential U has a unique form of a harmonic oscillator potential, and a mass gap arises. The result is a nonperturbative relativistic light-front quantum mechanical wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number n and orbital angular momentum L. Only one mass parameter κ appears. Light-front holography thus provides a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. We also show how the mass scale κ underlying confinement and hadron masses determines the scale Λ {ovr MS} controlling the evolution of the perturbative QCD coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the light-front and its embedding in AdS space, to the perturbative QCD regime computed to four-loop order. The result is an effective coupling defined at all momenta. The predicted value Λ {ovr MS }=0.328±0.034 GeV is in agreement with the world average 0.339±0.010 GeV. The analysis applies to any renormalization scheme.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Covariant Spectator Theory and Hadron Structure

We present the first results of a study on meson spectroscopy using a covariant formalism based on the Covariant Spectator Theory (CST). Our approach is derived directly in Minkowski space and it approximates the Bethe-Salpeter equation by taking effectively into account the contributions from both ladder and crossed ladder diagrams in the qq ? interaction kernel. A general Lorentz structure of the kernel is tested and chiral constraints on the kernel are discussed. Results for the pion form factor are also presented.

Peña, M. T.↗
DOE OSTI2016

Perspective on the Origin of Hadron Masses

The energy-momentum tensor in chiral QCD, T-mu nu, exhibits an anomaly, viz. Theta(0) := T-mu mu not equal 0. Measured in the proton, this anomaly yields m(p)(2), where m(p) is the proton's mass; but, at the same time, when computed in the pion, the answer is m(pi)(2) = 0. Any attempt to understand the origin and nature of mass, and identify observable expressions thereof, must explain and unify these two apparently contradictory results, which are fundamental to the nature of our Universe. Given the importance of Poincare-invariance in modern physics, the utility of a frame-dependent approach to this problem seems limited. That is especially true of any approach tied to a rest-frame decomposition of T-mu nu because a massless particle does not possess a rest-frame. On the other hand, the dynamical chiral symmetry breaking paradigm, connected with a Poincare-covariant treatment of the continuum bound-state problem, provides a straightforward, simultaneous explanation of both these identities, and also a diverse array of predictions, testable at existing and proposed facilities. From this perspective, = 0 owing to exact, symmetry-driven cancellations which occur between one-body dressing effects and two-body-irreducible binding interactions in any well-defined computation of the forward scattering amplitude that defines this expectation value in the pseudoscalar meson. The cancellation is incomplete in any other hadronic bound state, with a remainder whose scale is set by the size of one-body dressing effects.

Roberts, Craig D.↗
DOE OSTI2017

Polarized 3 He target and Final State Interactions in SiDIS

Jefferson Lab is starting a wide experimental program aimed at studying the neutron’s structure, with a great emphasis on the extraction of the parton transverse-momentum distributions (TMDs). To this end, Semi-inclusive deep-inelastic scattering (SiDIS) experiments on polarized $^3$He will be carried out, providing, together with proton and deuteron data, a sound flavor decomposition of the TMDs. Here, given the expected high statistical accuracy, it is crucial to disentangle nuclear and partonic degrees of freedom to get an accurate theoretical description of both initial and final states. In this contribution, a preliminary study of the Final State Interaction (FSI) in the standard SiDIS, where a pion (or a Kaon) is detected in the final state is presented, in view of constructing a realistic description of the nuclear initial and final states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

N* Experiments and Their Impact on Strong QCD Physics

Here, I give a brief overview of experimental studies of the spectrum and the structure of the excited states of the nucleon and what we learn about their internal structure. The focus is on the effort to obtain a more complete picture of the light-quark baryon excitation spectrum employing electromagnetic beams, and on the study of the transition form factors and helicity amplitudes and their dependence on the size of the four-momentum transfer $Q^2$, especially on some of the most prominent resonances. These were obtained in pion and eta electroproduction experiments off proton targets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Photo- and Electro-excitation of Bound Neutrons and Protons

Data for pion photo-productions off the neutron ( γn→πN ) have been mainly extracted from deuteron-target data ( γd→πNN ) by applying kinematical cuts thereby isolating the quasi-free samples. We critically explore if the neutron-target data obtained through this conventional procedure can be contaminated by final state interactions (FSI) and/or the kinematical cuts. The analysis is conducted with a theoretical model for γd→πNN that takes account of the impulse mechanisms supplemented by the NN and πN rescattering mechanisms. We show that the FSI effects still visibly remain in the extracted γ ‘n’ →πN unpolarized cross sections and polarization asymmetries E even after the kinematical cuts are applied. We also find the FSI effects on γ ‘n’ →π 0 n can be somewhat different from those on γ ‘p’ →π 0 p .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Hadron Spectroscopy and Dynamics from Light-Front Holography and Superconformal Algebra

QCD is not supersymmetrical in the traditional sense – the QCD Lagrangian is based on quark and gluonic fields, not squarks nor gluinos. However, its hadronic eigensolutions conform to a representation of superconformal algebra, reflecting the underlying conformal symmetry of chiral QCD and its Pauli matrix representation. The eigensolutions of superconformal algebra provide a unified Regge spectroscopy of meson, baryon, and tetraquarks of the same parity and twist as equal-mass members of the same 4-plet representation with a universal Regge slope. The pion $q\bar{q}$ eigenstate has zero mass for m q = 0. The superconformal relations also can be extended to heavy-light quark mesons and baryons. The combined approach of light-front holography and superconformal algebra also provides insight into the origin of the QCD mass scale and color confinement. A key observation is the remarkable dAFF principle which shows how a mass scale can appear in the Hamiltonian and the equations of motion while retaining the conformal symmetry of the action. When one applies the dAFF procedure to chiral QCD, a mass scale κ appears which determines universal Regge slopes, hadron masses in the absence of the Higgs coupling, and the mass parameter underlying the Gaussian functional form of the nonperturbative QCD running coupling: α s (Q 2 ) ∝ exp-Q 2 /4κ 2 , in agreement with the effective charge determined from measurements of the Bjorken sum rule. The mass scale κ underlying hadron masses can be connected to the parameter Λ $\overline{MS}$ in the QCD running coupling by matching its predicted nonperturbative form to the perturbative QCD regime. The result is an effective coupling α s (Q 2 ) defined at all momenta. In conclusion, one also obtains empirically viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

What Hath Weinberg Wrought? Reflections on What Weinberg’s Papers on ‘Nuclear Forces from Chiral Lagrangians’ did and did not Accomplish

Here, I discuss selected legacies of Weinberg's application of chiral Lagrangians to nuclear physics: (1) the use of the chiral expansion to organize the interaction of pions and photons with a nucleus; (2) the much-debated question of why and how the potential derived from a chiral Lagrangian should be inserted in the Schrodinger equation; (3) the emergence of "pionless EFT" as a tool for diagnosing universal correlations that are present in quantum few-body systems of very different sizes, and, perhaps most important of all, (4) an epistemological shift in what is expected of a nuclear-physics calculation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Nuclear axial current operators to fourth order in chiral effective field theory

We present the complete derivation of the nuclear axial charge and current operators as well as the pseudoscalar operators to fourth order in the chiral expansion relative to the dominant one-body contribution using the method of unitary transformation. We demonstrate that the unitary ambiguity in the resulting operators can be eliminated by the requirement of renormalizability and by matching of the pion-pole contributions to the nuclear forces. We give expressions for the renormalized single-, two- and three-nucleon contributions to the charge and current operators and pseudoscalar operators including the relevant relativistic corrections. We also verify explicitly the validity of the continuity equation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Antihelium-3 sensitivity for the GRAMS experiment

The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation balloon/satellite mission utilizing a Liquid Argon Time Projection Chamber (LArTPC) detector to measure both MeV gamma rays and antinuclei produced by dark matter annihilation or decay. The GRAMS can identify antihelium-3 events based on the measurements of X-rays and charged pions from the decay of the exotic atoms, Time of Flight (TOF), energy deposition, and stopping range. This paper shows the antihelium-3 sensitivity estimation using a GEANT4 Monte Carlo simulation. For the proposed long-duration balloon (LDB) flight program (35 days x 3 flights) and future satellite mission (2-year observation/10-year observation), the sensitivities become 1.47 × 10 −7 [m 2 s sr GeV/n] −1 and 1.55 × 10 −9 [m 2 s sr GeV/n] −1 /3.10 x 10 -10 [m 2 s sr GeV/n] −1 , respectively. The results indicate that GRAMS can extensively investigate various dark matter models through the antihelium-3 measurements.

Antihelium-3↗
DOE OSTI2014

High precision photon flux determination for photon tagging experiments

The Jefferson Laboratory PrimEx Collaboration has developed and implemented a method to control the tagged photon flux in photoproduction experiments at the 1% level over the photon energy range from 4.9 to 5.5 GeV. This method has been successfully implemented in a high precision measurement of the neutral pion lifetime. Here, we outline the experimental equipment and the analysis techniques used to accomplish this. These include the use of a total absorption counter for absolute flux calibration, a pair spectrometer for online relative flux monitoring, and a new method for post-bremsstrahlung electron counting.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

A threshold gas Cerenkov detector for the spin asymmetries of the nucleon experiment

In this study, we report on the design, construction, commissioning, and performance of a threshold gas Cerenkov counter in an open configuration, which operates in a high luminosity environment and produces a high photo-electron yield. Part of a unique open geometry detector package known as the Big Electron Telescope Array, this Cerenkov counter served to identify scattered electrons and reject produced pions in an inclusive scattering experiment known as the Spin Asymmetries of the Nucleon Experiment E07-003 at the Thomas Jefferson National Accelerator Facility (TJNAF) also known as Jefferson Lab. The experiment consisted of a measurement of double spin asymmetries A || and A ⊥ of a polarized electron beam impinging on a polarized ammonia target. The Cerenkov counter's performance is characterised by a yield of about 20 photoelectrons per electron or positron track. Thanks to this large number of photoelectrons per track, the Cerenkov counter had enough resolution to identify electron-positron pairs from the conversion of photons resulting mainly from π 0 decays.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗