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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 901 records · Page 50
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DOE OSTI2010

Higher order QED in high-mass e{sup +}e{sup -} pair production at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)

Lowest order and higher order QED calculations have been carried out for the RHIC high mass e{sup +}e{sup -} pairs observed by PHENIX with single zero-degree-calorimeter triggers. The lowest order QED results for the experimental acceptance are about two standard deviations larger than the PHENIX data. Corresponding higher order QED calculations are within one standard deviation of the data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Analysis of flux-integrated cross sections for quasi-elastic neutrino charged-current scattering off {sup 12}C at energies available at the MiniBooNE experiment

Flux-averaged and flux-integrated cross sections for quasi-elastic neutrino charged-current scattering on nuclei are analyzed. It is shown that the flux-integrated differential cross sections are less dependent on nuclear models than the flux-averaged ones. We calculate these cross sections using the relativistic distorted-wave impulse approximation and relativistic Fermi gas model with the Booster Neutrino Beamline flux and compare the results with the recent MiniBooNE experimental data. Within these models an axial mass M{sub A} is extracted from a fit of the measured d{sigma}/dQ{sup 2} cross section. The extracted value of M{sub A}=1.37{+-}0.05 GeV/c{sup 2} is consistent with the MiniBooNE result. While the measured and calculated double differential cross sections d{sigma}/dTdcos{theta} generally agree, the Fermi gas model predictions are typically lower than data at low muon energies and scattering angles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Charm and bottom production in inclusive double Pomeron exchange in heavy-ion collisions at energies available at the CERN Large Hadron Collider

The inclusive double Pomeron exchange cross section for heavy-quark pair production is calculated for nucleus-nucleus collisions at the Large Hadron Collider. The present estimate is based on hard diffractive factorization, corrected by absorptive corrections and nuclear effects. The theoretical uncertainties for nuclear collisions are investigated and a comparison to other approaches is presented. The production channels giving a similar final state configuration are discussed as well.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Charge conservation at energies available at the BNL Relativistic Heavy Ion Collider and contributions to local parity violation observables

Relativistic heavy ion collisions provide laboratory environments from which one can study the creation of a novel state of matter, the quark-gluon plasma. The existence of such a state is postulated to alter the mechanism and evolution of charge production, which then becomes manifest in charge correlations. We study the separation of balancing charges at kinetic freeze-out by analyzing recent results on balancing charge correlations for Au + Au collisions at {radical}(s{sub NN})=200 GeV. We find that in central collisions, the spatial points from which balancing charges are emitted are characterized by smaller relative angles. These results are consistent with the expectation that charge production occurred later in the collision, as would be expected for delayed hadronization. An alternative explanation would be that the charges were produced early, perhaps with a different mechanism where the charge production mechanism was altered from string breaking which tends to separate the charges in relative rapidity. The alternative explanation would also rely on the diffusion of charges being small. In addition we calculate the contributions from charge-balance correlations to STAR's local parity violation observable. We find that local charge conservation, when combined with elliptic flow, explains the bulk of STAR's measurement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Physics of Z{sup 0}/{gamma}*-tagged jets at energies available at the CERN Large Hadron Collider

Electroweak bosons produced in conjunction with jets in high-energy collider experiments is one of the principal final-state channels that can be used to test the accuracy of perturbative quantum chromodynamics calculations and to assess the potential to uncover new physics through comparison between data and theory. In this article we present results for the Z{sup 0}/{gamma}*+jet production cross sections at the CERN Large Hadron Collider (LHC) at leading and next-to-leading orders. In proton-proton reactions we elucidate up to O(G{sub F{alpha}s}{sup 2}) the constraints that jet tagging via the Z{sup 0}/{gamma}* decay dileptons provides on the momentum distribution of jets. In nucleus-nucleus reactions we demonstrate that tagged jets can probe important aspects of the dynamics of quark and gluon propagation in hot and dense nuclear matter and characterize the properties of the medium-induced parton showers in ways not possible with more inclusive measurements. Finally, we present specific predictions for the anticipated suppression of the Z{sup 0}/{gamma}{sup *}+jet production cross section in the quark-gluon plasma that is expected to be created in central lead-lead collisions at the LHC relative to the naive superposition of independent nucleon-nucleon scatterings.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nonequilibrium dynamics in heavy-ion collisions at low energies available at the GSI Schwerionen Synchrotron

The updated ultrarelativistic quantum molecular dynamics (UrQMD) model, a microscopic transport model, is used to study the directed and elliptic collective flows and the nuclear stopping in Au+Au collisions at incident energies covered by INDRA and lower-energy FOPI experiments. It is seen clearly that these observables are sensitive to both the potential terms (including isoscalar and isovector parts as well as the momentum dependent term) in the equation of state (EoS) and the collision term [including the Pauli blocking and the medium-modified nucleon-nucleon elastic cross section (NNECS)]. The momentum modifications of both, the mean-field potentials and the density dependent NNECS, are found to affect the collectivity of heavy-ion collisions. At INDRA energies ({<=}150 MeV/nucleon) the dynamic transport with a soft EoS with momentum dependence and with the momentum-modified density-dependent NNECS describes the directed flow exhibited by hydrogen isotopes (Z=1) emitted at midrapidity fairly well.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Elliptic flow at energies available at the CERN Large Hadron Collider: Comparing heavy-ion data to viscous hydrodynamic predictions

I compare the first viscous hydrodynamic prediction for integrated elliptic flow in Pb-Pb collisions at the Large Hadron Collider with the first data released by the ALICE Collaboration. These new data are found to be consistent with hydrodynamic extrapolations of the Relativistic Heavy-Ion Collider data with no change in medium parameters (e.g., average viscosity). I also discuss how, in general, a precise comparison of data to theoretical calculations requires an understanding of some subtleties of the measurement - most notably the cut on transverse momentum of the particles used and the differing sensitivities to flow fluctuations and nonflow effects of the various measurement methods.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Vector meson production in coherent hadronic interactions: Update on predictions for energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

In this Rapid Communication we update our predictions for the photoproduction of vector mesons in coherent pp and AA collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies using the color dipole approach and the Color Glass Condensate formalism. In particular, we present our predictions for the first run of the LHC at half energy and for the rapidity dependence of the ratio between the J/{Psi} and {rho} cross sections at RHIC energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Dimuon radiation at relativistic energies available at the CERN Super Proton Synchrotron within a (3 + 1)D hydrodynamic + cascade model

We analyze dilepton emission from hot and dense matter using a hybrid approach based on the ultrarelativistic quantum molecular dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. During the hydrodynamic stage, the production of lepton pairs is described by radiation rates for a strongly interacting medium in thermal equilibrium. In the low-mass region, hadronic thermal emission is evaluated by assuming vector meson dominance including in-medium modifications of the {rho} meson spectral function through scattering from nucleons and pions in the heat bath. In the intermediate-mass region, the hadronic rate is essentially determined by multipion annihilation processes. Emission from quark-antiquark annihilation in the quark gluon plasma (QGP) is taken into account as well. When the system is sufficiently dilute, the hydrodynamic description breaks down and a transition to a final cascade stage is performed. In this stage dimuon emission is evaluated as commonly done in transport models. By focusing on the enhancement with respect to the contribution from long-lived hadron decays after freezeout observed at the SPS in the low-mass region of the dilepton spectra, the relative importance of the different thermal contributions and of the two dynamical stages is investigated. We find that three separated regions can be identified in the invariant mass spectra. Whereas the very low and the intermediate-mass regions mostly receive contribution from the thermal dilepton emission, the region around the vector meson peak is dominated by the cascade emission. Above the {rho}-peak region the spectrum is driven by QGP radiation. Analysis of the dimuon transverse mass spectra reveals that the thermal hadronic emission shows an evident mass ordering not present in the emission from the QGP. A comparison of our calculation to recent acceptance-corrected NA60 data on invariant as well as transverse mass spectra is performed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Fluid dynamical prediction of changed v{sub 1} flow at energies available at the CERN Large Hadron Collider

Substantial collective flow is observed in collisions between lead nuclei at Large Hadron Collider (LHC) as evidenced by the azimuthal correlations in the transverse momentum distributions of the produced particles. Our calculations indicate that the global v{sub 1}-flow, which at RHIC peaked at negative rapidities (named third flow component or antiflow), now at LHC is going to turn toward forward rapidities (to the same side and direction as the projectile residue). Potentially this can provide a sensitive barometer to estimate the pressure and transport properties of the quark-gluon plasma. Our calculations also take into account the initial state center-of-mass rapidity fluctuations, and demonstrate that these are crucial for v{sub 1} simulations. In order to better study the transverse momentum flow dependence we suggest a new ''symmetrized''v{sub 1}{sup S}(p{sub t}) function, and we also propose a new method to disentangle global v{sub 1} flow from the contribution generated by the random fluctuations in the initial state. This will enhance the possibilities of studying the collective Global v{sub 1} flow both at the STAR Beam Energy Scan program and at LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Suppression of high-p{sub T} hadrons in Pb+Pb collisions at energies available at the CERN Large Hadron Collider

The nuclear modification factor R{sub AA}(p{sub T}) for large transverse momentum pion spectra in Pb+Pb collisions at {radical}(s)=2.76 TeV is predicted within the next-to-leading order perturbative QCD parton model. The effect of jet quenching is incorporated through medium-modified fragmentation functions within the higher-twist approach. The jet transport parameter that controls medium modification is proportional to the initial parton density, and the coefficient is fixed by data on the suppression of large-p{sub T} hadron spectra obtained at the BNL Relativistic Heavy Ion Collider. Data on charged hadron multiplicity dN{sub ch}/d{eta}=1584{+-}80 in central Pb+Pb collisions from the ALICE experiment at the CERN Large Hadron Collider are used to constrain the initial parton density both for determining the jet transport parameter and the 3 + 1 dimensional (3 + 1D) ideal hydrodynamic evolution of the bulk matter that is employed for the calculation of R{sub PbPb}(p{sub T}) for neutral pions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Shape and flow fluctuations in ultracentral Pb + Pb collisions at the energies available at the CERN Large Hadron Collider

In ultracentral heavy-ion collisions, anisotropic hydrodynamic flow is generated by density fluctuations in the initial state rather than by geometric overlap effects. For a given centrality class, the initial fluctuation spectrum is sensitive to the method chosen for binning the events into centrality classes. We show that sorting events by total initial entropy or by total final multiplicity yields event classes with equivalent statistical fluctuation properties, in spite of viscous entropy production during the fireball evolution. With this initial entropy-based centrality definition we generate several classes of ultracentral Pb + Pb collisions at CERN Large Hadron Collider energies and evolve the events using viscous hydrodynamics with nonzero shear but vanishing bulk viscosity. Comparing the predicted anisotropic flow coefficients for charged hadrons with CMS data we find that both the Monte Carlo Glauber (MC-Glb) and Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) models produce initial fluctuation spectra that are incompatible with the measured final anisotropic flow power spectrum, for any choice of the specific shear viscosity. In spite of this failure, we show that the hydrodynamic model can qualitatively explain, in terms of event-by-event fluctuations of the anisotropic flow coefficients and flow angles, the breaking of flow factorization for elliptic, triangular, and quadrangular flow measured by the CMS experiment. For elliptic flow, this factorization breaking is large in ultracentral collisions. Finally, we conclude that the bulk of the experimentally observed flow factorization breaking effects are qualitatively explained by hydrodynamic evolution of initial-state fluctuations, but that their quantitative description requires a better understanding of the initial fluctuation spectrum.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Shadowing effects on J/ψ and Υ production at energies available at the CERN Large Hadron Collider

Proton-nucleus collisions have been used as a intermediate baseline for the determination of cold medium effects. They lie between proton-proton collisions in vacuum and nucleus-nucleus collisions which are expected to be dominated by hot matter effects. Modifications of the quark densities in nuclei relative to those of the proton are well established although those of the gluons in the nucleus are not well understood. We focus on the effect of these on quarkonium production in proton-lead collisions at the LHC at a center of mass energy of 5.02 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Beam-energy dependence of charge balance functions from Au + Au collisions at energies available at the BNL Relativistic Heavy Ion Collider

Balance functions have been measured in terms of relative pseudorapidity ( Δη ) for charged particle pairs at the BNL Relativistic Heavy Ion Collider (RHIC) from Au + Au collisions at $\sqrt{s}$$_{NN}$ = 7.7 GeV to 200 GeV using the STAR detector. These results are compared with balance functions measured at the CERN Large Hadron Collider from Pb + Pb collisions at $\sqrt{s}$$_{NN}$ = 2.76 TeV by the ALICE Collaboration. The width of the balance function decreases as the collisions become more central and as the beam energy is increased. In contrast, the widths of the balance functions calculated using shuffled events show little dependence on centrality or beam energy and are larger than the observed widths. Balance function widths calculated using events generated by UrQMD are wider than the measured widths in central collisions and show little centrality dependence. The measured widths of the balance functions in central collisions are consistent with the delayed hadronization of a deconfined quark gluon plasma (QGP). Finally, the narrowing of the balance function in central collisions at $\sqrt{s}$$_{NN}$ = 7.7 GeV implies that a QGP is still being created at this relatively low energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Vector-boson-tagged jet production in heavy ion collisions at energies available at the CERN Large Hadron Collider [Vector boson-tagged jet production in heavy ion collisions at the LHC]

Here, vector-boson-tagged jet production in collisions of heavy nuclei opens new opportunities to study parton shower formation and propagation in strongly interacting matter. It has been argued to provide a golden channel that can constrain the energy loss of jets in the quark-gluon plasma created in heavy ion reactions. We present theoretical results for isolated-photon-tagged and Z 0 -boson-tagged jet production in Pb + Pb collisions with √s NN = 5.02TeV at the LHC. Specifically, we evaluate the transverse momentum imbalance x JV distribution and nuclear modification factor I AA of tagged jets and compare our theoretical calculations to recent experimental measurements by ATLAS and CMS collaborations. Our analysis, which includes both collisional and radiative energy losses, sheds light on their relative importance versus the strength of jet-medium interactions and helps quantify the amount of out-of-cone radiation of predominantly prompt quark-initiated jets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Effects of bulk viscosity and hadronic rescattering in heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

Here, we describe ultrarelativistic heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider with a hybrid model using the IP-Glasma model for the earliest stage and viscous hydrodynamics and microscopic transport for the later stages of the collision. We demonstrate that within this framework the bulk viscosity of the plasma plays an important role in describing the experimentally observed radial flow and azimuthal anisotropy simultaneously. Finally, we further investigate the dependence of observables on the temperature below which we employ the microscopic transport description.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Harmonic decomposition of three-particle azimuthal correlations at energies available at the BNL Relativistic Heavy Ion Collider

Here, we present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from √ s NN=7.7 to 200 GeV using the STAR detector. The quantity < cos(mΦ 1 +nΦ 2 –(m+n)Φ 3 ) >, with Φ being the azimuthal angles of the particles is evaluated as a function of √ s NN, collision centrality, transverse momentum, p T , pseudorapidity difference, Δη, and harmonics (m and n). These data provide detailed information on global event properties such as the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on Δη is observed for most harmonic combinations, which is consistent with breaking of longitudinal boost invariance. An interesting energy dependence is observed when one of the harmonics m,n, or m+n is equal to two, for which the correlators are dominated by the two-particle correlations relative to the second-harmonic event plane. These measurements can be used to constrain models of heavy-ion collisions over a wide range of temperature and baryon chemical potential.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗