Low Momentum Direct Photon Measurement

Direct photons have long been considered as golden probes to study the properties of the Quark Gluon Plasma (QGP). They do not interact strongly with the medium and are produced at all stages of the collision, hence carrying information of the entire evolution of the system to the detectors. The PHENIX experiment discovered a large excess of low pT photons in Au+Au collisions at √sNN = 200 GeV compared to reference p+p collisions, which has been interpreted as thermal radiation from the QGP and hadron gas medium. At the same time, the excess photons show a large elliptic and triangular flow. These results are challenging for the current theoretical models to describe simultaneously, because on one hand the large yield suggests early stage emissions when the temperature is high, on the other hand the large anisotropy is expected to be formed only at later stages of the collision when the system has cooled off and the thermal photon production rate is expected to be smaller. Using a variety of high statistics datasets across different collision systems and energies in PHENIX, simultaneous analyses of yields and azimuthal asymmetries of direct photons with higher precision are performed to provide more constraints to the theoretical calculations. In this talk, we will present recent results on low pT direct photons measured via their external conversions to electron-positron pairs, including new results from Au+Au at lower beam energies of 39 and 62.4 GeV, as well as Cu+Cu at 200GeV.

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Study the early stage of heavy ion collisions with direct photons

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194514602300 ◽

2014 ◽

Vol 29 ◽

pp. 1460230 ◽

Cited By ~ 1

Author(s):

Fu-Ming Liu ◽

Sheng-Xu Liu

Keyword(s):

Collective Motion ◽

Early Stage ◽

Heavy Ion ◽

Gluon Plasma ◽

Transverse Momentum Spectrum ◽

Direct Photons ◽

Ion Collisions ◽

Phenix Collaboration ◽

Early Beginning ◽

Hadronic Data

Based on the modelling of the collective motion in AuAu collisions at [Formula: see text] at centrality 0-20% and 20-40% and PbPb collisions at [Formula: see text] at centrality 0-40% with a 3+1D event-averaged ideal hydrodynamics constrained with hadronic data, we study the transverse momentum spectrum and elliptic flow of direct photons and find that the recent direct photon data from both PHENIX collaboration at RHIC and ALICE collaboration at LHC favour an early beginning of collective expansion (τ0 < 0.6 fm/c) and a late formation of quark gluon plasma (τ ~ 2 fm/c).

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The ϕ meson production in small collision systems observed by PHENIX

EPJ Web of Conferences ◽

10.1051/epjconf/202225805010 ◽

2022 ◽

Vol 258 ◽

pp. 05010

Author(s):

Mariia Mitrankova ◽

Alexander Berdnikov ◽

Yaroslav Berdnikov ◽

Dmitry Kotov ◽

Iurii Mitrankov

Keyword(s):

Collective Behavior ◽

Quark Gluon Plasma ◽

Meson Production ◽

Theoretical Models ◽

Gluon Plasma ◽

Hadron Production ◽

Enhancement Effect ◽

Light Hadron ◽

200 Gev ◽

Strangeness Enhancement

The measurements of light hadron production in small collision systems (such as p+Al, p+Au, d+Au, 3He+Au) may allow to explore the quarkgluon plasma formation and to determine the main hadronization mechanism in the considered collisions. Such research has become particularly crucial with the observation of the light hadrons collective behavior in p/d/3He+Au collisions at √SNN = 200 GeV and in p+Al collisions at the same energy at forward and backward rapidities. Among the large variety of light hadrons, ϕ meson is of particular interest since its production is sensitive to the presence of the quark-gluon plasma. The paper presents the comparison of the obtained experimental results on ϕ meson production to different light hadron production in p+Al and 3He+Au at √SNN = 200 GeV at midrapidity. The comparisons of ϕ meson production in p+Al, p+Au, d+Au, and 3He+Au collisions at √SNN = 200 GeV at midrapidity to theoretical models predictions (PYTHIA model and default and string melting versions of the AMPT model) are also provided. The results suggest that the QGP can be formed in p/d/3He+Au collisions, but the volume and lifetime of the produced medium might be insufficient for observation of strangeness enhancement effect. Conceivably, the main hadronization mechanism of ϕ meson production in p+Al collisions is fragmentation, while in p/d/3He+Au collisions this process occurs via coalescence.

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Measurements of the Υ Meson Production in Au + Au Collisions by the STAR Experiment

Proceedings ◽

10.3390/proceedings2019010046 ◽

2019 ◽

Vol 10 (1) ◽

pp. 46

Author(s):

Oliver Matonoha

Keyword(s):

Theoretical Calculations ◽

Meson Production ◽

Heavy Ion ◽

Gluon Plasma ◽

Relativistic Heavy Ion Collisions ◽

Decay Channels ◽

Ion Collisions ◽

200 Gev ◽

Star Experiment ◽

Colour Screening

In ultra-relativistic heavy-ion collisions, creation of a novel state of matter, the quark-gluon plasma (QGP), has been observed. Suppressed production of quarkonia, caused by the colour screening of the binding force, has been proposed as a direct evidence of the QGP formation. At RHIC energies, other phenomena such as the regeneration and co-mover absorption, are expected to have a small effect for the bottomonium family, which makes Υ a cleaner probe of the screening effect compared to the J / ψ meson. In these proceedings, the latest measurements of the Υ production suppression in Au + Au collisions at s NN = 200 GeV via the di-muon and di-electron decay channels by the STAR experiment at RHIC are presented and compared with data from the LHC and theoretical calculations. Moreover, Υ production measurements in p + p and p + Au collisions are also reported, providing a baseline and a quantification of the cold nuclear matter effects, respectively.

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Exploring the Partonic Phase at Finite Chemical Potential in and out-of Equilibrium

Particles ◽

10.3390/particles3010015 ◽

2020 ◽

Vol 3 (1) ◽

pp. 178-192 ◽

Cited By ~ 1

Author(s):

O. Soloveva ◽

P. Moreau ◽

L. Oliva ◽

V. Voronyuk ◽

V. Kireyeu ◽

...

Keyword(s):

Cross Sections ◽

Chemical Potential ◽

Transport Coefficients ◽

Gluon Plasma ◽

Entropy Density ◽

Baryon Chemical Potential ◽

Equilibrium Study ◽

200 Gev ◽

Quasiparticle Model ◽

Scattering Cross Sections

We study the influence of the baryon chemical potential μ B on the properties of the Quark–Gluon–Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature T c from lattice Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity η and bulk viscosity ζ over entropy density s, i.e., η / s and ζ / s in the ( T , μ ) plane and compare to other model results available at μ B = 0 . The out-of equilibrium study of the QGP is performed within the Parton–Hadron–String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential μ B in each individual space-time cell where partonic scattering takes place. The traces of their μ B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV ≤ s N N ≤ 200 GeV.

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Signatures of QGP at RHIC and the LHC

AAPPS Bulletin ◽

10.1007/s43673-021-00014-3 ◽

2021 ◽

Vol 31 (1) ◽

Author(s):

T. Niida ◽

Y. Miake

Keyword(s):

Heavy Ion Collisions ◽

Heavy Ion ◽

Gluon Plasma ◽

High Energy ◽

Jet Quenching ◽

Theoretical Studies ◽

Debye Screening ◽

Direct Photons ◽

Ion Collisions ◽

Experimental And Theoretical Studies

AbstractThe progress over the 30 years since the first high-energy heavy-ion collisions at the BNL-AGS and CERN-SPS has been truly remarkable. Rigorous experimental and theoretical studies have revealed a new state of the matter in heavy-ion collisions, the quark-gluon plasma (QGP). Many signatures supporting the formation of the QGP have been reported. Among them are jet quenching, the non-viscous flow, direct photons, and Debye screening effects. In this article, selected signatures of the QGP observed at RHIC and the LHC are reviewed.

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Direct photons in 200 GeV , , and Au+Au from PHENIX

Nuclear Physics A ◽

10.1016/j.nuclphysa.2006.06.125 ◽

2006 ◽

Vol 774 ◽

pp. 731-734 ◽

Cited By ~ 15

Author(s):

S. Bathe

Keyword(s):

Direct Photons ◽

200 Gev

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A Modified Thermal Boundary Resistance Model for FCC Structures

ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2 ◽

10.1115/mnhmt2009-18175 ◽

2009 ◽

Author(s):

Ruijie Zhao ◽

Yunfei Chen ◽

Kedong Bi ◽

Meihui Lin ◽

Zan Wang

Keyword(s):

Phonon Scattering ◽

Phonon Dispersion ◽

Theoretical Calculations ◽

Theoretical Models ◽

Md Simulations ◽

Boundary Resistance ◽

Nonequilibrium Molecular Dynamics ◽

Thermal Boundary Resistance ◽

Inelastic Channel ◽

The Right

A modified lattice-dynamical model is proposed to calculate the thermal boundary resistance at the interface between two fcc lattices. The nonequilibrium molecular dynamics (MD) simulation is employed to verify the theoretical calculations. In our physical model, solid crystal argon is set at the left side and the right side structure properties are tunable by setting the atomic mass and the interactive energy strength among atoms with different values. In the case of mass mismatch, the predictions of the lattice-dynamical (LD) model agree well at low temperature while the calculations of the diffuse mismatch model (DMM) based on the detailed phonon dispersion agree well at high temperature with the MD simulations. The modified LD model, considering a partially specular and partially diffuse phonon scattering, can explain the simulations reasonably in the whole temperature rage. The good agreement between the theoretical calculations and the simulations may be attributed to that phonon scattering mechanisms are dominated by elastic scattering at the perfect interfaces. In the case of interactive energy strength mismatch, the simulations are under the predictions of both the theoretical models, which may be attributed to the fact that this mismatch can bring about an outstanding contribution to opening up an inelastic channel for heat transfer at the interfaces.

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ELECTRON/POSITRON EXCESSES IN THE COSMIC RAY SPECTRUM AND POSSIBLE INTERPRETATIONS

International Journal of Modern Physics D ◽

10.1142/s0218271810018268 ◽

2010 ◽

Vol 19 (13) ◽

pp. 2011-2058 ◽

Cited By ~ 74

Author(s):

YI-ZHONG FAN ◽

BING ZHANG ◽

JIN CHANG

Keyword(s):

Dark Matter ◽

Supernova Remnant ◽

Cosmic Ray ◽

Theoretical Models ◽

New Physics ◽

Observational Constraints ◽

Correct Interpretation ◽

Observational Feature ◽

Electron Positron ◽

Observational Status

The data collected by ATIC, PPB-BETS, FERMI-LAT and HESS all indicate that there is an electron/positron excess in the cosmic ray energy spectrum above ~100 GeV, although different instrumental teams do not agree on the detailed spectral shape. PAMELA also reported clearly the excessive feature of the fraction of positron above several GeV, but with no excess in antiprotons. Here we review the observational status and theoretical models of this interesting observational feature. We pay special attention to various physical interpretations proposed in the literature, including modified supernova remnant models for the e± background, new astrophysical sources, and new physics (the dark matter models). We suggest that although most models can make a case to interpret the data, with the current observational constraints the dark matter interpretations, especially those invoking annihilation, require much more exotic assumptions than some other astrophysical interpretations. Future observations may present some "smoking-gun" observational tests to differentiate different models and to identify the correct interpretation of the phenomenon.

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