W. W. Jacobs
Production of W bosons in longitudinally polarized pp collisions provides an excellent tool to probe the flavor-dependence of sea quark polarizations in the polarized proton. Current status and future plans for the W physics program with the STAR detector at RHIC are presented along with remarks concerning our knowledge of the nature and origin of the partonic sea.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
继续探索
We report on recent results of the longitudinal double-spin asymmetry A_LL from the STAR and PHENIX experiments. Data were collected in longitudinally polarized proton-proton collisions at a center-of-mass energy of 200 GeV. The results added new constraints to the polarized gluon distribution function g(x) with the probed x range of 0:02 < x < 0:3. The results lead to the importance of probing small x.
We present preliminary results of Non-Photonic Electron (NPE) production, NPE-hadron azimuthal correlation as well as NPE elliptic flow studies at midrapidity using a data set with high statistics and low photon conversion background from $Au+Au$ collisions at $\sqrt {S_{NN}} = 200$ GeV collected at RHIC in Run 2010.
Three-dimensional source images for mid-rapidity, low transverse momentum kaon and pion pairs have been extracted from central Au+Au collisions data at \sqrt{s_{NN}} = 200 GeV by the STAR experiment at RHIC. The pion source function displays significant non-Gaussian features implying a finite pion emission duration. On the other hand, the kaon source function is essentially Gaussian, consistent with instantaneous emission from the fireball.
The first measurement of the dielectron continuum at RHIC energies was performed by the PHENIX experiment for Au+Au collisions at sqrt(s_{NN}) = 200 GeV. Mass spectra for different centralities are presented and compared with the expectations from hadron decays.
The PHENIX Experiment on the Relativistic Heavy Ion Collider (RHIC) with its use of beams of polarized protons, provides a unique environment of hard scattering between gluons and quarks complementary to that provided by deep inelastic scattering (DIS). Polarized proton proton collisions can directly probe the polarized gluon and anti-quark distributions as the collisions couple the color charges of the participants. We will give a brief overview of the PHENIX Spin Program and we will report recent results of the many probes accessible to the PHENIX experiment.
During RHIC 2010 run, STAR has collected a large amount of minimum-bias, central and high $p_{T}$ trigger data in Au+Au collisions at $\sqrt{s_{NN}} = 39$, 62.4 and 200 GeV with detector configuration for minimum photonic conversion background. In this article we report on a new high precision measurement of non-photonic electron mid-rapidity invariant yield, improved nuclear modification factor and $v_{2}$ in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. We also present measurements of mid-rapidity invariant yield at $\sqrt{s_{NN}} = 62.4$ and $v_{2}$ at $\sqrt{s_{NN}} = 39$ and 62.4 GeV.
Two-pion correlation functions in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV have been measured by the STAR (Solenoidal Tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The HBT parameters display a weak energy dependence over a broad range in $\sqrt{s_{NN}}$.
Direct photon production in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV has been measured. The result is compared to several theoretical calculations, and found that it is not inconsistent with ones including thermal radiation from QGP or jet-photon conversion process on top of a NLO pQCD expectation. The direct photon contribution in dilepton measurement is also evaluated.
Neutral pions ($π^0$) in $\sqrt{s_\mathrm{NN}}$ = 200 GeV and 62.4 GeV Au+Au collisions were measured at RHIC-PHENIX Year-4 Run. In $\sqrt{s_\mathrm{NN}}$ = 200 GeV, $π^0$ specta are measured up to p$_\mathrm{T}$ = 20 GeV/$c$. %PHENIX extended the p$_\mathrm{T}$ region of A strong suppression by a factor of $\sim$ 5 is observed and stays almost constant up to 20 GeV/$c$.
We report the measurement of first (\textit {n} = 1) and higher order(\textit{n} = 2-5) harmonic coefficients ($v_{n}$) of the azimuthal anisotropy in the distribution of the particles produced in U+U collisions at $\sqrt{s_{NN}}$ =193 GeV, recorded with the STAR detector at RHIC. The differential measurement of $(v_{n})$ is presented as a function of transverse momentum ($p_{T}$) and centrality. We also present $v_{n}$ measurement in the ultra-central collisions. These data may provide strong constraints on the theoretical models of the initial condition in heavy ion collisions and the transp…
We report on the first measurement of Mutual Coulomb Dissociation in heavy ion collisions. We employ forward calorimeters to measure neutron multiplicity at beam rapidity in peripheral collisions. The cross-section for simultaneous electromagnetic breakup of Au nuclei at $\sqrt{s_{NN}}=130$ GeV is $σ_{MCD}=3.67\pm 0.25$ barns in good agreement with calculations.
Two particle azimuthal correlations with strange trigger particles ($K^0_S,Λ,Ξ$) are presented in Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR at RHIC. The near-side associated yield is investigated as a function of centrality, $p_T$, and strangeness content of the trigger to investigate possible flavour or meson/baryon differences. The system size dependence of both the jet-like correlations and the long range pseudorapidity correlations is studied to give insight into the origin of these two components.
We present charged particle densities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at Sqrt{s_NN}=200 GeV. For the 5% most central events we obtain dN_ch/deta(eta=0) = 625 +/- 55 and N_ch(-4.7<= eta <= 4.7) = 4630+-370, i.e. 14% and 21% increases, respectively, relative to Sqrt{s_NN}=130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around mid-rapidity. These results constrain current models of particle production at the highest RHIC energy.
The production of Lambda(1520) in p+p and Au+Au collisions provided by the RHIC at sqrt{s_NN}=200 GeV are investigated using the STAR detector. A preliminary Sigma(1385) signal is also shown. Models predict that a late rescattering phase in ultra-relativistic heavy ion collisions should lower the measured yields of these resonances. This reduction is presently confirmed through the Lambda(1520)/Lambda ratio which has been calculated for p+p collisions and compared with Au+Au collisions.
Direct photon production in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV has been measured in the $p_T$ range of 1$<$$p_T$$<$5 GeV/$c$. The yield as acfunction of centrality is in agreement with published data of the RHIC 2002 run, and with results from a new method that explores very low mass dileptons. The result is compared to several theoretical calculations, and it is found that the measurement is not inconsistent with calculations including thermal photon contributions.
The hyperon-hyperon and hyperon-nucleon interactions are important in search for exotic hadrons such dibaryon as a bound state of two baryons. $Λ$-$Λ$ correlation has been measured in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 200 GeV at RHIC-STAR experiment using high statistics data recently taken, which has been found to clearly show the anti-correlation. The first measurements of p-$Ξ$ and $Ξ$-$Ξ$ correlations in Au+Au collisions have been shown. The p-$Ξ$ correlation function shows the strong attractive interaction, which is consistent with HAL QCD calculation. $Ξ$-$Ξ$ correlation has als…
One of the primary goals of high-energy heavy-ion collisions is to establish the QCD phase diagram and search for possible phase boundaries. The planned RHIC energy scan program will explore this exciting physics topic using heavy-ion collisions at various center of mass energies. The first test run with Au+Au collisions at $\sqrt{s_{NN}}$ = 9.2 GeV took place in early 2008. We present the results on identified particle ratios, azimuthal anisotropy parameters (v1 and v2) and HBT at midrapidity using data from this run. These results are compared to data for both lower and higher center of mass…
Particle correlations at small relative velocities can be used to study the space-time evolution of hot and expanding system created in heavy ion collisions. Baryon and antibaryon source sizes extracted from baryon-baryon correlations complement the information deduced from the correlation studies of identical pions. Correlations of non-identical particles are sensitive also to the space-time asymmetry of their emission. High statistics data set of STAR experiment allows us to present the results of baryon-baryon correlation measurements at various centralities and energies, as well as to take…
In non-central nuclear collisions, the created matter should exhibit strong vorticity, which induces spin polarization. Global polarization is a good tool to investigate the dynamics of the system. Global polarization of $Λ$ and $\barΛ$ hyperons has been measured at $\sqrt{s_{\mathrm{NN}}}$ = 2.4 GeV - 5.02 TeV in various experiments. We have measured the global polarization of $Λ$ hyperons in Au+Au collisions with fixed-target configuration at $\sqrt{s_{\mathrm{NN}}}$ = 7.2 GeV at RHIC-STAR experiment. The non-zero signal is observed and it follows the global trend of $Λ$ global polarization …
The PHENIX experiment at RHIC measured $ω$, $η$ and $K_{S}^{0}$-meson production at high $p_{T}$ in $p+p$, $d+Au$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ $GeV$. Measurements performed in different hadronic decay channels give consistent results. The measured ratios of all three mesons to $π^{0}$ are found to be flat as a function of $p_{T}$ in $p+p$ collisions and equal to $ω/π^{0}=0.81\pm0.02\pm0.07$, $η/π^{0}=0.48\pm0.02\pm0.02$ and $K_{S}^{0}/π^{0}=0.45\pm0.01\pm0.05$. Nuclear modification factor measured for $ω$-mesons in central Au+Au collisions is $R_{AA}=0.4\pm0.15$.
We present the first measurements of the double spin asymmetries A_NN and A_SS at sqrt{s}=200 GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). The data were collected in the four momentum transfer t range 0.01<|t|<0.03 (GeV/c)^2. The measured asymmetries, which are consistent with zero, allow us to estimate upper limits on the double helicity-flip amplitudes phi_2 and phi_4 at small t as well as on the difference Delta(sigma_T) between the total cross sections for transversely polarized protons with antiparallel or parallel spin …
Thermal photons can provide information on the temperature of the new state of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are expected to be the dominant direct photon source. Therefore, a possible excess compared to a pure decay photon signal due to a thermal photon contribution should be seen in the double ratio (gamma/gamma(pi^0))_{Measured}/(gamma/gamma(pi^0))_{Simulated}, if sufficient accuracy can be reached. We present a method to reconstruct direct photons by measuring e^+e^- pairs from external photon conversions.
The production of $W^{\pm}$ bosons in longitudinally polarized $\vec{p}+\vec{p}$ collisions at RHIC provides a new means of studying the spin-flavor asymmetries of the proton sea quark distributions. Details of the $W^{\pm}$ event selection in the $e^{\pm}$ decay channel at mid-rapidity are presented, along with preliminary results for the production cross section and parity-violating single-spin asymmetry, $A_L$, from the STAR Collaboration's 2009 data at $\sqrt{s}=500$ GeV.
The pi0 meson has been a crucial proble for observing jet quenching in ultrarelativistic heavy-ion collisions at RHIC. Measurements of the eta meson in the same collisions have also shed light on a possible dependence of the observed suppression on the particle species. The preliminary pi0 nuclear modification factor R_AA from the 2004 RHIC run allowed a first systematic comparison between a precise measurement with high statistics and theoretical calculations, constraining model parameters such as the initial gluon density dN^g/dy, and the transport coefficient qhat. The final pi0 spectra and…
Large transverse single-spin asymmetries (TSSA) in hadron production at forward rapidity have been observed in polarized $p$+$p$ interactions for many decades, over a large range of center-of-mass energies, and have led to the investigation of spin-momentum correlations such as the Sivers and Collins effects. In the last few years, it has been discovered at RHIC that these single-spin asymmetries may be enhanced or suppressed in $p$+$A$ collisions, and the nuclear-size and centrality dependence have been studied. A variety of phenomena have been observed and likely they do not have all a singl…
The polarized proton beams at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory provide a unique environment to observe hard scattering between gluons and quarks. The PHENIX experiment has recorded collisions at $\sqrt(s_{NN})=$200 GeV and 62.4 GeV to yield data which are complementary to those measured by deep inelastic scattering experiments. Polarized proton-proton collisions can directly probe the polarized gluon and anti-quark distributions as the collisions couple the color charges of the participants. The PHENIX detector is well suited to measure many final-state par…
We present the results for the measurement of $ϕ$ meson production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion Collider (RHIC). Using the event mixing technique, spectra and yields are obtained from the $ϕ\to K^{+}K^{-}$ decay channel for different centrality bins in Au+Au collisions and in pp collisions. We observe that the spectrum shape in Au+Au collisions depends weakly on the centrality and the shape of the spectrum in pp collisions is significantly different from that in Au+Au collisions. In Au+Au collisions, the extracted yield of $ϕ$ meson is flat…
The production of $W$ bosons in polarized $p+p$ collisions at RHIC provides an excellent tool to probe the proton's sea quark distributions. At leading order $W^{-(+)}$ bosons are produced in $\bar{u}+d\,(\bar{d}+u)$ collisions, and parity-violating single-spin asymmetries measured in longitudinally polarized $p+p$ collisions give access to the flavor-separated light quark and antiquark helicity distributions. In this proceedings we report preliminary results for the single-spin asymmetry, $A_L$ from data collected in 2012 by the STAR experiment at RHIC with an integrated luminosity of 72 pb$^…
Thermal photons can provide information on the temperature of the new state of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are expected to be the dominant direct photon source. Therefore, a possible excess compared to a pure decay photon signal due to a thermal photon contribution should be seen in the double ratio (γ/γ(π^{0}))_{Measured}/(γ/γ(π^{0}))_{Simulated}, if sufficient accuracy can be reached. We present a method to reconstruct direct photons by measuring e^{+}e^{-}--pairs from external photon conversions.
We analyse the recently available experimental data on direct photon productions from Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV RHIC and from Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV LHC energies. The transverse momentum ($p_T$) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at temperatures $T_i$=404 and 546 MeV with initial thermalisation times $τ_i$=0.2 and 0.1 fm/c respectively for RHIC and LHC energies. The theoretical evalutions agree reasonably well with the experimental observations. The thermal window for the LHC energy is justified t…
We present the preliminary results on direct photon interferometry measurements in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 and 200 GeV using the STAR (Solenoidal Tracker at RHIC) detector. Photons are reconstructed via $e^+/e^-$ conversions in STAR Time Projection Chamber(TPC) and energy deposited by photons in STAR Barrel Electromagnetic Calorimeter(BEMC). The two-photon correlations are measured using (1) both photons measured using BEMC; (2) one photon from conversions and the other measured with BEMC. Both the methodologies and the possible constraints in the correlation function m…
We perform a study of $W$-boson production in polarized proton-proton collisions through next-to-next-to-leading order (NNLO) in perturbative QCD. This calculation is required to extend the extraction of polarized parton distribution functions to NNLO accuracy. We present differential distributions at $\sqrt{s}=510$ GeV, relevant for comparison to measurements from the Relativistic Heavy Ion Collider (RHIC). The NNLO QCD corrections significantly reduce the scale dependence of the cross section. We compare the longitudinal single-spin asymmetries as a function of lepton pseudorapidity to RHIC …
The PHENIX and STAR Collaborations at the Relativistic Heavy-Ion Collider and ALICE, CMS, ATLAS and LHCb Collaborations at the Large Hadron Collider have measured the production of charmonium and bottonium states as well as open heavy flavor hadrons via their hadronic and semi-leptonic decays at mid-rapidity and in the semi-muonic decay channel at forward rapidity in pp, p--A and A--A collisions in an energy domain that ranges from $\sqrt{s}$ = 0.2 TeV to $\sqrt{s}$ = 13 TeV in pp collisions and from $\sqrt{s_{\rm NN}}$ = 0.2 TeV to $\sqrt{s_{\rm NN}}$ = 5.02 TeV in A--A collisions. In this co…
We study inclusive heavy quarkonium production with definite polarizations in polarized proton-proton collisions using the non-relativistic QCD color-octet mechanism. We present results for rapidity distributions of cross sections and spin asymmetries for the production of J/psi and psi' with specific polarizations in polarized p-p collisions at \sqrt s = 200 GeV and 500 GeV at the RHIC within the PHENIX detector acceptance range.
The transverse energy distributions ($E_{T}$) have been measured for Au + Au collisions at $\sqrt{s_{NN}} = 62.4$ GeV by the STAR experiment at RHIC. They have been obtained from two measurements, the hadronic transverse energy ($E_{T}^{had}$) and the electromagnetic transverse energy($E_{T}^{em}$). $E_{T}^{had}$ has been measured from the tracks obtained by Time Projection Chamber (TPC) excluding the electrons and positrons. $E_{T}^{em}$ has been obtained by the STAR Barrel Electromagetic Calorimeter (BEMC) which measures the energy of electrons, positrons and photons. The measure of transver…
Identified pi^[+/-] K^[+/-], p and p-bar transverse momentum spectra at mid-rapidity in sqrt(s_NN)=130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. The multiplicity densities scale faster than the number of participating nucleons. Kaon and nucleon yields per participant increase faster than the pion yields. In central collisions at high transverse momenta (p_T greater than 2 GeV/c), anti-proton and proton yields a…
We present the first measurements of the $ρ(770)^0$, $K^*$(892), $Δ$(1232)$^{++}$, $Σ$(1385), and $Λ$(1520) resonances in $d$+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV, reconstructed via their hadronic decay channels using the STAR detector at RHIC. The masses and widths of these resonances are studied as a function of transverse momentum ($p_T$). We observe that the resonance spectra follow a generalized scaling law with the transverse mass ($m_T$). The $<p_T>$ of resonances in minimum bias collisions is compared to the $<p_T>$ of $π$, $K$, and $\bar{p}$. The $ρ^0/π^-$, $K^*/K^-$, $Δ^{++}…
The recent preliminary results from central Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 130 GeV from the STAR experiment at RHIC are presented and discussed along with the results on the $Λ$(1520) production in cental Pb+Pb and p+p collisions at $\sqrt{s} = $ 17 GeV from the NA49 experiment at the SPS. The $Λ$(1520) is measured with the invariant mass reconstruction of the decay products in the hadronic channel (K$^{-}$, p). The mean $Λ$(1520) multiplicity scaled by the number of participants decreases from p+p to Pb+Pb collisions at the same energy of $\sqrt{s}$ = 17 GeV. An upper limit estima…
We study inclusive $χ_{cJ}$ production with definite polarizations in polarized proton-proton collisions at $\sqrt{s}$ = 200 GeV and 500 GeV at RHIC by using non-relativistic QCD (NRQCD) color-octet mechanism. We present results of rapidity distribution of $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ production with specific polarizations in polarized p-p collisions at RHIC within the PHENIX detector acceptance range. We also present the corresponding results for the spin asymmetries.
In this analysis we measure the azimuthal angle($ϕ$) dependence of hadrons with respect to the reaction plane ($Ψ_{RP}$) in events that were triggered by a high-$p_T$ $π^0$ of 5-10 GeV. Fitting the distribution of hadrons with a function of the type $ξ(1+2v_2\cos{(2(ϕ-Ψ_{RP})}))$, we observe that there is no significant statistical difference between $v_2$ inclusive hadrons and those hadrons from hard scattering events. We also compare the near-side jet widths using PYTHIA simulations with $h^{\pm}$-$h^{\pm}$ correlations in Au+Au at $\sqrt{s_{NN}}=200$ GeV.
We report on the first measurement of the single spin analyzing power (A_N) at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result, averaged over the whole t-interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A_N. The difference could be explained by an additional contribution of a hadronic spi…
Measurements from the RHIC experiments show strong suppression of high-pT hadrons in central Au+Au collisions. The PHENIX experiment has observed strong suppression of $π^0$ and charged hadron yields in central Au+Au collisions for pT > 5 GeV/c regardless of pT and particle species. The observed suppression is interpreted in terms of energy loss of quarks in a high-density medium. The PHENIX Year-4 Au+Au measurements have extended the pT reach of the $π^0$ spectra to 20 GeV/c. And the PHENIX Year-5 Cu+Cu measurements performed for the study of particle production in a lighter system and they c…
The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transversely or longitudinally polarized proton beams at = 200-500 GeV to gain deeper insigh t into the spin structure and dynamics of the proton. These studies provide fundamental insight into Quantum Chromodynamics (QCD). One of the main objectives is the determination of the polarized gluon distribution function, g, through the measurement of the longitudinal double-spin asymmetry, ALL, for various processes. Inclusive hadron and jet prod…
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 \sqrt{s_{NN}}=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.
Results on physics at RHIC using outgoing leptons and photons will be presented from Au+Au collisions at nucleon-nucleon c.m. energies $\sqrt{s_{NN}}=130$ and 200 GeV and from p-p collisions at $\sqrt{s}=200$ GeV. Introduction and motivation will be presented both from the theoretical and experimental perspectives. Topics include open charm production via single $e^{\pm}$, $J/Ψ\to e^+ + e^-$, $μ^+ + μ^-$ and inclusive photon production.
We present the mid-rapidity $(D^{0} + \bar{D^{0}})/2$ yield measured in $\sqrt{s_{NN}}$ = 200 GeV Cu+Cu collisions at RHIC via direct reconstruction through the $Kπ$ decay channel. A charm cross-section is reported and compared to theoretical predictions and to previous RHIC experimental results.
Direct photons are an important tool for the detection of the quark-gluon plasma in ultra-relativistic nucleus-nucleus collisions. Direct-photon measurements were made in Pb+Pb collisions at sqrt{s_NN}=17.2 GeV and in Au+Au collisions at sqrt{s_NN}=200 GeV. These results are reviewed and compared with model calculations.
We present a detailed study of particle production at mid-rapidity in proton + proton collisions at RHIC for sqrt(s)=200GeV. The transverse momentum spectra and the <pT> of inclusive hadrons and identified particles as a function of multiplicity are measured in minimum bias, "soft" and "hard" event classes. It is found that the multiplicity dependence of <pT> in soft events in proton + proton collisions does not change from RHIC to Tevetron while there is no such scaling behavior in minimum-bias and hard events. The baryon and strangeness production derived from the particle ratios of K-/pi- a…
Electromagnetic probes are ideally suited to investigate hot and dense matter produced in high energy heavy ion collisions. They do not undergo strong interactions and thus probe the time evolution of the collision. The dielectron continuum is rich in physics. Dalitz decays of light hadrons and direct decays of vector mesons, which might be modified in the medium, and correlated charm decays contribute to the spectrum. Furthermore, exotic states, e.g quasi-particles predicted to exist in the medium only beyond the phase transition, might leave their footprint in the continuum. Although correla…
The status of the search for direct photons in Au+Au collisions at sqrt{s_NN} = 130 GeV and sqrt{s_NN} = 200 GeV with the PHENIX experiment is presented. Within errors, no excess of direct photons was found in a first analysis pass done on a limited data set. Significantly reduced systematic and statistical uncertainties are expected in future analyses.
STAR's measurements of directed flow ($v_1$) around midrapidity for $π^{\pm}$, K$^{\pm}$, K$_S^0$, $p$ and $\bar{p}$ in Au + Au collisions at $\sqrtsNN = 200$ GeV are presented. A negative $v_1(y)$ slope is observed for most of produced particles ($π^{\pm}$, K$^{\pm}$, K$_{S}^{0}$ and $\bar{p}$). In 5-30% central collisions a sizable difference is present between the $v_1(y)$ slope of protons and antiprotons, with the former being consistent with zero within errors. The $v_1$ excitation function is presented. Comparisons to model calculations (RQMD, UrQMD, AMPT, QGSM with parton recombination,…
Transverse momentum spectra for neutral pions have been measured by the WA98 experiment in sqrt{s_{nn}}=17.3 GeV Pb+Pb collisions at the CERN SPS and by the PHENIX experiment in sqrt{s_{nn}}=130 GeV Au+Au collisions at RHIC. The neutral pion yields in central collisions for both reaction systems are compared to scaled transverse momentum spectra for nucleon-nucleon reactions at the respective energy. At SPS energies neutral pion production at high $p_T$ is enhanced compared to the n+n reference while at RHIC a significant suppression of high-pT neutral pions is observed.
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, and $p$($\bar{p}$) are studied at mid-rapidity $(\lvert y \rvert < 0.1)$ for different centrality classes. We also present mid-rapidity measurement of particle yields $(dN/dy)$ and particle ratios in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV. The kinetic freeze-out parameters ($T_{kin}$ and $\langle β\rangle$) are extracted from parti…
The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is carrying out a spin physics program in high-energy polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200-500\,$GeV to gain a deeper insight into the spin structure and dynamics of the proton. One of the main objectives of the spin physics program at RHIC is the extraction of the polarized gluon distribution function based on measurements of gluon initiated processes, such as hadron and jet production. The STAR detector is well suited for the reconstruction of various final states involving jets, $…
Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity in Pb+Pb reactions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-}, by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV. The modification factor R_{AA} shows a rapid increase with transverse momentum in the covered region. The modification factor R_{CP} shows saturation well below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200 GeV RHIC results closely in the available transve…
Experimental results on heavy-quark production in proton-proton, deuteron-gold, and gold-gold collisions at sqrt(s_(NN)) = 200 GeV at the Relativistic Heavy Ion Collider (RHIC) are reviewed.
We present high transverse momentum ($p_T$) measurements made at the Relativistic Heavy Ion Collider (RHIC) for Au+Au, d+Au, and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV, as well as for Au+Au collisions at $\sqrt{s_{NN}} = 62$ GeV. We observe a suppression in the yield of high $p_T$ hadrons measured in central Au+Au collisions, relative to the yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions. This observation, together with the absence of such a suppression in d+Au collisions, leads to the conclusion that a dense medium is formed in central Au+Au collisions.
Direct photons provide a insightful tool to study the different stages of a heavy ion collision, especially the formation of a quark-gluon plasma, without being influenced by the strong interaction and hadronization processes. The yield of direct photons can be determined based on the inclusive photon yield and the background from hadronic decays. We present a new analysis technique applied to PHENIX Run4 Au+Au dataset. It uses strict particle identification(PID) in the Electromagnetic Calorimeter(EMCal) and a charged particle veto to extract a clean photon signal. These photons are then tagge…
We report the first measurements of azimuthal anisotropy at midrapidity originated from the dipole asymmetry due to fluctuations in the initial geometry in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. The signal is almost symmetric in pseudorapidity and we report it as a function of pseudorapidity and transverse momentum for different centrality. Results are compared with available model predictions
The J/$ψ$ yields in heavy ion collisions are expected to be a promising probe of deconfined matter, since theoretical models predict that the J/$ψ$ production could be strongly suppressed due to color screening effect in a Quark Gluon Plasma. In addition, one of the interesting predictions that has emerged recently is the J/$ψ$ enhancement at RHIC energy via competing mechanisms such as recombination. The PHENIX collaboration has measured J/$ψ$ production via its decay into lepton pairs in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV. The nuclear modification factor $R_{\rm AA}$ for…
扫码添加微信好友，提出您的宝贵建议 👇
💡 备注请填写：网站反馈
发表机构由 AI 从论文文本抽取，如发现错误，欢迎反馈修正建议。