Suppression In Au Research Articles

Beam energy and system size dependence of heavy flavor production at STAR

We report the measurements of quarkonia (J/ψ and ψ(2S)) in heavyion collisions via the e+e− decay channel at midrapidity (|y| < 1) by the STAR experiment. The centrality and transverse momentum dependence of the yield ratio of ψ(2S) to J/ψ is measured for the first time in heavy-ion collisions at RHIC. These results, together with the new measurement of collision energy dependence of inclusive J/ψ suppression in Au+Au collisions, allow for a systematic study of the quarkonium production in the medium. In addition, we present the first measurement of J/ψ polarization in heavy-ion collisions at RHIC in both the Helicity and the Collins-Soper frames, which provides a new insight for studying the properties of the Quark-Gluon Plasma created in heavy-ion collisions.

Measurement of Sequential ϒ Suppression in Au+Au Collisions at sqrt[s_{NN}]=200 GeV with the STAR Experiment.

We report on measurements of sequential ϒ suppression in Au+Au collisions at sqrt[s_{NN}]=200 GeV with the STAR detector at the Relativistic Heavy Ion Collider (RHIC) through both the dielectron and dimuon decay channels. In the 0%-60% centrality class, the nuclear modification factors (R_{AA}), which quantify the level of yield suppression in heavy-ion collisions compared to p+p collisions, for ϒ(1S) and ϒ(2S) are 0.40±0.03(stat)±0.03(sys)±0.09(norm) and 0.26±0.08(stat)±0.02(sys)±0.06(norm), respectively, while the upper limit of the ϒ(3S) R_{AA} is 0.17 at a 95%confidence level. This provides experimental evidence that the ϒ(3S) is significantly more suppressed than the ϒ(1S) at RHIC. The level of suppression for ϒ(1S) is comparable to that observed at the much higher collision energy at the Large Hadron Collider. These results point to the creation of a medium at RHIC whose temperature is sufficiently high to strongly suppress excited ϒ states.

Determining the jet transport coefficient q̂ from inclusive hadron suppression measurements using Bayesian parameter estimation

We report a new determination of q̂, the jet transport coefficient of the quark-gluon plasma. We use the JETSCAPE framework, which incorporates a novel multistage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the Matter and Lbt jet quenching models, are compared to experimental measurements of inclusive hadron suppression in Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and Pb+Pb collisions at the CERN Large Hadron Collider (LHC). The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of q̂ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of Matter and Lbt. In the multistage approach, the switch between Matter and Lbt is governed by a virtuality scale Q0. Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of q̂/T3 extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature T, with 90% credible region (CR) depending on the specific choice of model configuration. The choice of Matter+Lbt, with switching at virtuality Q0, has 90% CR of 2<q̂/T3<4 for pT,jet>40 GeV/c. The value of Q0, determined here for the first time, is in the range 2.0–2.7 GeV.9 MoreReceived 23 February 2021Accepted 21 July 2021DOI:https://doi.org/10.1103/PhysRevC.104.024905©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHydrodynamic modelsJets & heavy flavor physicsParticle & resonance productionRelativistic heavy-ion collisionsTechniquesBayesian methodsNuclear Physics

Measurement of inclusive J/ψ suppression in Au+Au collisions at [formula omitted] GeV through the dimuon channel at STAR

J/ψ suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive J/ψ production at mid-rapidity through the dimuon decay channel in Au+Au collisions at sNN=200 GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The J/ψ yields are measured in a wide transverse momentum (pT) range of 0.15 GeV/c to 12 GeV/c from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the J/ψ yield is suppressed by a factor of approximately 3 for pT>5 GeV/c relative to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The J/ψ nuclear modification factor displays little dependence on pT in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by J/ψ mesons in the QGP.

Latest results on ϒ production in heavy-ion collisions from the STAR experiment

We report on the latest measurements of the production of ϒ mesons in heavy-ion collisions from the STAR experiment at RHIC. New measurements of the nuclear modification factors of the ϒ(1S+2S+3S) and ϒ(1S) states in U+U collisions at are presented as a function of the number of participants (Npart) in the collisions. In addition, the suppression of ϒ(1S) and ϒ(2S+2S) is presented versus the quark-antiquark binding energy. Preliminary results on ϒ suppression in Au+Au collisions at , reconstructed via the dimuon channel, are also reported.

Jet-like correlations with direct-photon and neutral-pion triggers at sNN=200 GeV

Azimuthal correlations of charged hadrons with direct-photon ($\gamma_{dir}$) and neutral-pion ($\pi^{0}$) trigger particles are analyzed in central Au+Au and minimum-bias $p+p$ collisions at $\sqrt{s_{_{NN}}} = 200$ GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity from central Au+Au collisions are compared with $p+p$ collisions to quantify the suppression in Au+Au collisions. The suppression of the away-side associated-particle yields per $\gamma_{dir}$ trigger is independent of the transverse momentum of the trigger particle ($p_{T}^{\mathrm{trig}}$), whereas the suppression is smaller at low transverse momentum of the associated charged hadrons ($p_{T}^{\mathrm{assoc}}$). Within uncertainty, similar levels of suppression are observed for $\gamma_{dir}$ and $\pi^{0}$ triggers as a function of $z_{T}$ ($\equiv p_T^{\mathrm{assoc}}/p_T^{\mathrm{trig}}$). The results are compared with energy-loss-inspired theoretical model predictions. Our studies support previous conclusions that the lost energy reappears predominantly at low transverse momentum, regardless of the trigger energy.

Suppression of ϒ production in [formula omitted] and [formula omitted] collisions at [formula omitted

We report measurements of ϒ meson production in p+p, d+Au, and Au+Au collisions using the STAR detector at RHIC. We compare the ϒ yield to the measured cross section in p+p collisions in order to quantify any modifications of the yield in cold nuclear matter using d+Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p+p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for ϒ(1S+2S+3S) in the rapidity range |y|<1 in d+Au collisions of RdAu=0.79±0.24(stat.)±0.03(syst.)±0.10(p+p syst.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au+Au collisions, we measure a nuclear modification factor of RAA=0.49±0.1(stat.)±0.02(syst.)±0.06(p+psyst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state ϒ mesons in Au+Au collisions. The additional suppression in Au+Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in d+Au is still needed before any definitive statements about the nature of the suppression in Au+Au can be made.

New Measurement of Heavy-Flavor Electron v2 and Separation of Bottom and Charm Using VTX in PHENIX

Heavy quarks are important probes to understand the properties of the Quark Gluon Plasma (QGP) created in the relativistic heavy-ion collision. The PHENIX measurement of electrons from heavy-flavor decays shows large flow and strong suppression in Au+Au collisions at 200 GeV [1][2], which is not well understood. In these proceedings, we will present both the new PHENIX heavy-flavor electron v2 results in Au+Au collisions at 62.4 GeV collisions using the Hadron Blind Detector (HBD) and the latest PHENIX measurement of charm and bottom separately in p+p collisions at 200 GeV with the recently installed Silicon Vertex Track (VTX).

STRONGLY INTERACTING QGP AND QUARKONIUM SUPPRESSION AT RHIC AND LHC ENERGIES

We have developed an equation of state for strongly interacting quark–gluon plasma (QGP) in the framework of strongly coupled plasma with appropriate modifications to take account of color and flavor degrees of freedom and the interactions among themselves. For this purpose we used the effective potential to improve the plasma parameter (Γ) by correcting the full Cornell potential with a dielectric function embodying the effects of the deconfined medium and not its Coulomb part alone and obtain the equation of state in terms of Γ. Our results on thermodynamic observables viz. pressure, energy density, speed of sound etc. nicely fit to the results of lattice equation of state for gluon, massless as well massive flavored plasma. We have then employed our equation of state to estimate the quarkonium suppression in an expanding QGP produced in the relativistic heavy-ion collisions. We have found that our predictions matches with the recent PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions at BNL RHIC within the limit of other uncertainties. We have also predicted for the ϒ suppression in Pb+Pb collisions at LHC energy which could be tested in the ALICE experiments at CERN LHC.

Recent PHENIX results on open heavy flavor

Throughout the history of the RHIC physics program, questions concerning the dynamics of heavy quarks have generated much experimental and theoretical investigation. A major focus of the PHENIX experiment is the measurement of these quarks through their semi-leptonic decay channels at mid and forward rapidity. Heavy quark measurements in p+p collisions give information on the production of heavy flavor, without complications from medium effects. New measurements in d +Au and Cu+Cu indicate surprising cold nuclear matter effects on these quarks at midrapidity and provide a new baseline for interpretation of the observed suppression in Au+Au collisions. When considered all together, these measurements present a detailed study of nuclear matter across a wide range of system size and temperature. Here, we present preliminary PHENIX measurements of non-photonic electron spectra and their centrality dependence in d+Au and Cu+Cu and discuss their implications on the current understanding of parton energy loss in the nuclear medium.

Measurement of [formula omitted] and γ in d+Au collisions at [formula omitted] by PHENIX experiment

Previous results indicated that high p T particle suppression in Au+Au interactions is a final state effect, since R d A ratios were compatible with unity, albeit within large experimental errors. It is important to test this conclusion to higher precision since the modification of structure functions may be involved. Recent d+Au data taken in 2008 improve the integrated luminosity by about a factor of thirty compared to the 2003 data. A more precise measurement of both π 0 and γ at higher p T will shed new light on whether the initial state in the heavy nuclei is modified.

Anomalous ϕ Meson Suppression in Au+Au Collisions at [formula omitted] Measured by the PHENIX Experiment at RHIC

The PHENIX experiment at RHIC has measured the ϕ-meson production at mid-rapidity in p + p , d+Au, Cu+Cu and Au+Au collisions at s N N = 200 GeV via the K +K − decay mode. The transverse momentum spectra of the ϕ-meson and the nuclear modification factor as a function of centrality are reviewed here.

Formula omitted] production in heavy ion collisions and gluon saturation

We calculate the inclusive J / ψ production in heavy ion collisions including the effects of gluon saturation in the wave functions of the colliding nuclei. We argue that the dominant production mechanism in proton–nucleus and nucleus–nucleus collisions for heavy nuclei is different from the one in hadron–hadron interactions. We find that the rapidity distribution of primary J / ψ production is more peaked around midrapidity than the analogous distribution in elementary pp collisions. We discuss the consequences of this fact on the experimentally observed J / ψ suppression in Au–Au collisions at RHIC energies.

J/ψ suppression and p T spectra in RHIC and LHC energy collisions

In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy, $\sqrt{s}=200$ GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T J/ψ. Sequential melting of charmonium states (χ c , ψ ′ and J/ψ), with melting temperatures $T_{\chi_{c}}=T_{\psi^{\prime}}\approx1.2T_{c}$ , T J/ψ≈2T c and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ p T spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ p T spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy, $\sqrt{s}=5500$ GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ p T distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC.

Sequential melting of charmonium states in an expanding quark–gluon plasma and J/ψ suppression at RHIC and LHC energy collisions

We have developed a hydrodynamic model to study sequential melting of charmonium states in an expanding quark–gluon plasma (QGP) medium. According to the initial fluid temperature profile, J/ψ's are randomly distributed in the transverse plane. As the fluid evolves in time, the free streaming J/ψ's are suppressed if the local fluid temperature exceeds a critical temperature. PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions at mid-rapidity are explained by sequential melting of the charmonium states, χc, ψ′ and J/ψ, in the expanding medium. The critical temperatures TJ/ψ ≈ 2.09Tc and agree with lattice-motivated calculations. The feed-down fraction F depends on whether the cold nuclear matter effect is included or not. It changes from F = 0.3 with cold nuclear matter effect included to F = 0.5 when the effect is neglected. The model fails to reproduce the PHENIX data on the centrality dependence of J/ψ suppression in Cu+Cu collisions at mid-rapidity, indicating that the mechanism of J/ψ suppression is different in Au+Au and Cu+Cu collisions. We also use the model to predict for the centrality dependence of J/ψ suppression in Pb+Pb collisions at LHC energy, = 5500 GeV. In LHC energy, J/ψ's are more suppressed in mid central collisions than in Au+Au collisions at RHIC energy.

Quantitative constraints on the transport properties of hot partonic matter from semi-inclusive single high transverse momentum pion suppression in Au+Au collisions atsNN=200GeV

The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum pi(0)'s in Au+Au collisions at root s(NN) = 200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN(g)/dy, the medium transport coefficient , or the initial energy-loss parameter epsilon(0). We find that high-transverse-momentum pi(0) suppression in Au+Au collisions has sufficient precision to constrain these model-dependent parameters at the +/- 20-25% (one standard deviation) level. These constraints include only the experimental uncertainties, and further studies are needed to compute the corresponding theoretical uncertainties.

J/ψ suppression in the threshold model at RHIC and LHC energy

In the QGP-based threshold model (Blaizot et al 2000 Phys. Rev. Lett. 85 4012, Blaizot and Ollitrault 1996 Phys. Rev. Lett. 77 1703), in addition to the normal nuclear absorption, J/ψ's are subjected to an ‘anomalous’ suppression such that above a threshold density nJ/ψ, all the J/ψ's are melted. In the threshold model we have analyzed the recent PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions at RHIC. Feedback from decay of the state χ is accounted for. J/ψ's are anomalously suppressed above a threshold density, nJ/ψ = 3.57 ± 0.17 fm−2. Threshold density for anomalous suppression of the state χ is uncertain to a large extent, nχ = 0.32 ± 0.32 fm−2. The fraction F of the state χ cannot be determined unambiguously, depending on the nuclear absorption, it can vary from 20% to 40%. We have also predicted for the suppression in Pb+Pb collisions at LHC energy. In central Pb+Pb collisions, J/ψ's are suppressed by a factor of 3–4. The suppression pattern is rather similar to that in Au+Au collisions, if not slighty less in central collisions. Using the PHENIX data on the participant number dependence of the Bjorken energy density, we have also estimated the QGP formation time. For critical temperature Tc = 192 MeV, the estimated QGP formation time ranges between 0.07 and 0.09 fm c−1.

Formula omitted] suppression in [formula omitted] collisions at RHIC: Colour screening scenario in the bag model at variable participant numbers

We have modified the colour screening theory of Chu and Matsui by properly incorporating bag model equation of state for quark–gluon plasma (QGP). We have also chosen the pressure parametrization rather than parameterizing energy density in the transverse plane. We assume that the QGP dense medium is expanding in the longitudinal direction obeying Bjorken boost invariant scaling law. Sequential melting of χc, ψ′ and J/ψ is also considered in this scenario. We have applied above formulation to the recent PHENIX experimental data of J/ψ suppression in Au+Au collisions at RHIC. We find that the model gives a good description of data at mid-rapidity in terms of survival probability versus number of participants without any necessity of implementing (3+1)-dimensional expansion of the deconfined medium.

J/ψproduction in Au+Au and Cu+Cu collisions atsNN=200GeV and the threshold model

Using the quark gluon plasma (QGP) motivated threshold model, where all the $J/\ensuremath{\psi}$'s are suppressed above a threshold density, we have analyzed the recent PHENIX data on the participant number dependence of the nuclear modification factor for $J/\ensuremath{\psi}$'s, in Au+Au collisions, at RHIC energy, $\sqrt{s}{}_{\mathit{NN}}=200$ GeV. Centrality dependence of midrapidity $J/\ensuremath{\psi}$ suppression in Au+Au collisions are well explained in the model for threshold density ${n}_{c}\ensuremath{\approx}3.6\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}2}$. PHENIX data on $J/\ensuremath{\psi}$ suppression at forward rapidity data are not explained in the model. The analysis strongly supports deconfined matter formation in central Au+Au collisions at midrapidity. We have also analyzed the preliminary PHENIX data on $J/\ensuremath{\psi}$ suppression in Cu+Cu collisions. Cu+Cu data are not explained in the threshold model.

J/ψproduction in Au+Au collisions atsNN=200GeV and the nuclear absorption

It is shown that a quantum chromodynamics-based nuclear absorption model, with few parameters fixed to reproduce experimental $J/\ensuremath{\psi}$ yield in 200 GeV proton-proton/proton-nucleon and 450 GeV proton-nucleon collisions, can explain the preliminary PHENIX data on the centrality dependence of $J/\ensuremath{\psi}$ suppression in Cu+Cu collisions at Relativistic Heavy Ion Collider (RHIC) energy, $\sqrt{{s}_{\mathit{NN}}}=200$ GeV. However, the model does not give a satisfactory description for the preliminary PHENIX data on the centrality dependence of $J/\ensuremath{\psi}$ suppression in Au+Au collisions. The analysis suggests that in Au+Au collisions, $J/\ensuremath{\psi}$ are suppressed in a medium unlike the medium produced in CERN Super Proton Synchrotron energy nuclear collisions or in RHIC energy Cu+Cu collisions.