Lijuan Ruan
The di-electron analysis for 200 GeV p+p collisions is presented in this article. The cocktail simulations of di-eletrons from light flavor meson decays and heavy flavor decays are reported and compared with data. The perspectives for di-lepton measurements in Au+Au collisions are discussed.
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In this contribution we report $e^{+}e^{-}$ spectra with various invariant mass and p$_{T}$ differentials in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV and U$+$U collisions at $\sqrt{s_{NN}}$=193 GeV. The structure of the t ($t\approx p^2_{\mathrm{T}}$) distributions of these mass regions will be shown and compared with the same distributions in ultra-peripheral collisions. Additionally, this contribution discusses first measurements of $μ^{+}μ^{-}$ invariant mass spectra from STAR's recently installed Muon Telescope Detector (MTD) in p$+$p and Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 Ge…
We present STAR's measurement of the $e^{+}e^{-}$ continuum as a function of centrality, invariant mass, and transverse momentum for U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Also reported are the acceptance-corrected $e^{+}e^{-}$ invariant mass spectra for minimum-bias Au+Au collisions at $\sqrt{s_{NN}}$ = 27, 39, and 62.4 GeV and U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV. The connection between the integrated $e^{+}e^{-}$ excess yields normalized by charge particle multiplicity ($dN_{ch}/dy$) at mid-rapidity and the lifetime of the fireball is discussed.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured single electrons at midrapidity and single muons at forward and backward rapidities (1.2<|y|< 2.2) for p+p and d+Au collisions at sqrt(sNN)=200 GeV. The inclusive lepton spectra exhibit excesses over light hadron sources. The excesses are attributed to semileptonic decays of charm and bottom hadrons and compared to the perturbative QCD predictions. The NLO pQCD calculation underpredicts the excess lepton production in {\it p+p} collisions. The excess lepton production in {\it d+Au} collisions scales with $N_{coll}$ at mi…
We present recent results from Al(beam)+Au(target) collisions at $\sqrt{s_{NN}}=4.9$ GeV and Au+Au collisions at $\sqrt{s_{NN}}=4.5$\kern 0.16667em GeV from the STAR fixed-target (FXT) program. We report transverse mass spectra of protons, $K^0_S$ and $Λ$, rapidity density distributions of $π^\pm$, $K^0_S$ and $Λ$, directed flow of protons, $π^\pm$, $K^0_S$ and $Λ$, and elliptic flow of protons and $π^{\pm}$. These are the first measurements of pion directed and elliptic flow in this energy range at RHIC. Pion and proton elliptic flow show mass ordering. Measurements are compared with the publ…
We present the ALICE results on the nuclear modification factor and elliptic flow of electrons and muons from open heavy-flavour hadron decays at mid-rapidity and forward rapidity in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 and 5.02 TeV for different centrality intervals. The results are compared to model calculations that include interactions of heavy quarks with the medium.
Measurements of direct photon production in p+Pb and p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$ are presented. Upper limits on the direct photon yield as a function of $p_\mathrm{T}$ are derived and compared to the results for Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 17.3$ GeV. The production of the $η$ meson, which is an important input to the direct photon signal extraction, has been determined in the $η\rightarrow 2γ$ channel for p+C collisions at $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.
The phase diagram of strongly interacting matter can be explored by analyzing data of heavy-ion collisions at different center of mass collision energies. For investigating the space-time structure of the hadron emission source, HBT correlation measurements are among the best tools. In this paper we present the latest results from the RHIC PHENIX experiment on such measurements in $\sqrt{s_{\rm NN}}=$ 39 GeV and 62 GeV Au+Au collisions.
In this paper we present the study of the azimuthal correlation function of non-photonic electrons with low-pT hadrons produced in Cu+Cu collision at sqrt(s_NN)=200 GeV measured by STAR experiment at RHIC. Possible modification of the awayside peak is observed.
Negatively charged hadron (h-) production in Au+Au collisions at BNL-RHIC is studied with the STAR experiment. Results are presented on h- multiplicity, pseudorapidity and transverse momentum distributions at sqrt(s_NN) = 130 GeV.
We report on the pT dependence of nuclear modification factors ($R_{CP}$) for Ks, Lambda, Xi and the Anti-Lambda/Ks ratios at mid-rapidity from Au+Au collisions at \sqrt{s_{NN}} = 39, 11.5 and 7.7 GeV. At \sqrt{s_{NN}} = 39 GeV, the $R_{CP}$ data shows a baryon/meson separation at intermediate pT and a suppression for Ks for pT up to 4.5 GeV/$c$; the Anti-Lambda/Ks shows baryon enhancement in the most central collisions. However, at \sqrt{s_{NN}} = 11.5 and 7.7 GeV, $R_{CP}$ shows much less baryon/meson separation and Anti-Lambda/Ks shows almost no baryon enhancement. These observations indica…
We investigate modification of the bottom quark production due to cold nuclear matter effects (CNM) at mid-rapidity in d+Au collisions at $\sqrt{s_{NN}} = 200$ GeV at RHIC. Our results indicate that bottom production is not suppressed due to CNM effects in those collisions. We also found that shadowing and initial $k_T$ breadboarding for charm quarks explains at low $p_T$ ($p_T < 3$ GeV/c) the enhancement of heavy flavor decay electron yield in d+Au collisions at $\sqrt{s_{NN}} = 200$ GeV compared to p+p.
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…
Upper limits on direct photon production were determined as a function of the transverse momentum for 0.7 < pT <= 3.2 GeV/c with the WA98 experiment in p+C and p+Pb collisions at sqrt(sNN) = 17.4 GeV. The results are compared to direct photon measurements in Pb+Pb collisions at sqrt(sNN) = 17.3 GeV by WA98. Implications for a possible thermal direct photon contribution are discussed.
We report the measurements of $p_T$ spectra of $K^*$ up to intermediate $p_T$ region in mid-rapidity through its hadronic decay channel using the STAR detector in Au+Au and Cu+Cu collisions at $\sqrt{s_{\mathrm{NN}}}$= 62.4 GeV and 200 GeV. Particle ratios such as $K^{*}/K$ and $K^{*}/ϕ$ is used to understand the rescattering and regeneration effect on $K^{*}$ production in the hadronic medium. The $K^*$ $v_{2}$ measurement using a high statistics Au+Au 200 GeV dataset and nuclear modification factor measurement supports the quark coalescence model of particle production in the intermediate $p…
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.
Measurements of heavy quark production and suppression in ultra-relativistic nuclear collisions probe the interactions of heavy quarks with the hot, dense medium created in the collisions. ATLAS has measured heavy quark production in $\sqrtsnn = 2.76$ \TeV \PbPb collisions via semi-leptonic decays of open heavy flavour hadrons to muons. Results are presented for the per-event muon yield as a function of muon transverse momentum, \pT, over the range of $4 < \pT < 14$ \GeV. The centrality dependence of the muon yields is characterized by the "central to peripheral" ratio, \Rcp. Muon production i…
The STAR Experiment at RHIC is capable of a wide variety of measurements of the production of strange hadrons in nuclear collisions. Measurements of the relative production of strange baryons, antibaryons, and kaons can shed light on the baryon densities achieved in these collisions and on the validity of models for production yields. We will present here preliminary results on these measurements at RHIC energies of sqrt(s_NN) = 130 GeV and 200 GeV and discuss comparisons to models.
The PHENIX experiment has measured direct photons at $\sqrt{s_{NN}}$ = 200 GeV in $p+p$, $d$+Au and Au+Au collisions. For $p_{T}$ $<$ 4 GeV/$c$, the internal conversion into $e^{+}e^{-}$ pairs has been used to measure the direct photons in Au+Au.
The STAR Collaboration presents new measurements of inclusive charged hadron distributions for $p_{T} <$ 12 GeV/c from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Charged hadron suppression at high $p_{T}$ is similar in shape and magnitude at all centralities to that observed previously at $\sqrt{s_{NN}}$ = 130 GeV for $p_{T} <$ 6 GeV/c. The ratio of spectra from central and peripheral Au+Au collisions shows that hadron suppression is approximately constant within 6 $< p_{T} <$ 12 GeV/c. The ratios of charged hadron spectra at the two beam energies show a 15-20% increase in yield at low $p_…
The measurement of J/{psi} azimuthal anisotropy is presented as a function of transverse momentum for different centralities in Au+Au collisions at {sqrt{s_{NN}}} = 200 GeV. The measured J/{psi} elliptic flow is consistent with zero within errors for transverse momentum between 2 and 10 GeV/c. Our measurement suggests that J/{psi} with relatively large transverse momentum are not dominantly produced by coalescence from thermalized charm quarks, when comparing to model calculations.
Azimuthal correlations between high energy photons from $π^0$ decay ($p_T^γ < 10.5$ GeV) and charged hadrons ($p_T^{hadron}$ above a threshold of 2, 3 or 4 GeV/c) have been measured in p+p and d+Au collisions at $\sqrt{s}=200$ GeV. Clear jet-like correlations are observed at $Δϕ=0$ and 180 degrees, with peak widths decreasing with increasing $p_T^{hadron}$. Jet $<j_T>$ and $\sqrt{< k_T^2 >}$ in d+Au collisions are deduced from the distributions. {\it These results are presented in Quark Matter 2004 poster session.
In this paper we present the study of the azimuthal correlation function of non-photonic electrons with low-pT hadrons produced in Cu+Cu collision at sqrt(s_NN) = 200 GeV measured by STAR experiment at RHIC. Possible modification of the awayside peak is observed.
New measurements are presented for charged hadron azimuthal correlations at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV. They are compared to earlier measurements obtained at sqrt(s_NN) = 130 GeV and in Pb+Pb collisions at sqrt(s_NN) = 17.2 GeV. Sizeable anisotropies are observed with centrality and transverse momentum (p_T) dependence characteristic of elliptic flow (v_2). For a broad range of centralities, the observed magnitudes and trends of the differential anisotropy, v_2(p_T), change very little over the collision energy range sqrt(s_NN) = 62-200 GeV, indicating sa…
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.
We present elliptic flow, $v_2$, measurements for charged and identified particles at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5 and 39 GeV at STAR. We compare the inclusive charged hadron $v_2$ to those from high energies at RHIC ($\sqrt{s_{NN}}$ = 62.4 and 200 GeV), at LHC ($\sqrt{s_{NN}}$ = 2.76 TeV). A significant difference in $v_2$ between baryons and anti-baryons is observed and the difference increases with decreasing beam energy. We observed the $v_2$ of $ϕ$ meson is systematically lower than other particles in Au+Au collisions at $\sqrt{s_{NN}}$ = 11.5 GeV.
In this talk, we report an analysis of elliptic flow ($v_2$), non-flow ($δ_{2}$), and $v_2$ fluctuations ($σ_{v_{2}}$) for the STAR collaboration at middle rapidity in $\sqrt{s_{_{NN}}}=200$ GeV Au+Au collisions. We compare the results to models of the fluctuations in the initial eccentricity of the overlap zone.
Different regions on the QCD phase diagram can be investigated by varying the collision energy and the centrality in heavy-ion collisions. In our latest measurements at the PHENIX experiment at RHIC, we utilize Lévy-type sources to describe the measured HBT correlation functions. In this paper we report the current status of the analysis of the centrality and beam energy dependence of the Lévy source parameters in Au+Au collisions from $\sqrt{s_{NN}}$ = 15 GeV to $\sqrt{s_{NN}}$ = 200 GeV.
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.
We report preliminary results of hypertriton observation in heavy-ion collisions at RHIC. We have identified 157 +- 30 candidates in the current sample containing ~10^8 Au+Au events at \sqrt{s_{NN}} = 200 GeV. The production rate of hypertriton is close to that of helium 3. No extra penalty factor is observed for hypertriton, in contrast to results observed at the AGS.
The BRAHMS collaboration has measured inclusive proton and anti-proton spectra at several rapidities (0 < y < 3) for Au+Au collisions at sqrt(s_NN) = 200 GeV. Rapidity densities of protons, anti-protons, and net-protons [N(p)-N(p-bar)] are presented as a function of rapidity.
The yields of identified particles have been measured at RHIC for Au+Au collisions at sqrt{s_NN} = 200 GeV using the PHOBOS spectrometer. The ratios of antiparticle to particle yields near mid-rapidity are presented. The first measurements of the invariant yields of charged pions, kaons and protons at very low transverse momenta are also shown.
In this proceedings, we present our first measurements of $ϕ$ meson and $Ξ^-$ hyperon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.
Mid-rapidity Omega and anti-Omega production in Au+Au collisions at RHIC is studied with the STAR experiment. We report preliminary results on yields and spectra at $\sqrt{s_{NN}}$ = 130 and 200 GeV. Production relative to negatively charged hadrons (h-) as well as thermal freeze-out and collective expansion are discussed.
We present $ΛΛ$ correlation measurements in heavy-ion collisions for Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV using the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). The Lednický-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the $ΛΛ$ correlation function and interaction parameters for di-hyperon searches are discussed.
The properties of the phi-meson have been measured via its e+e- and K+K- decay channels in Au+Au collisions at sqrt{s_NN} = 200 GeV by the PHENIX experiment. The preliminary yields and temperatures derived for the minimum bias and several centrality bins in both decay channels are presented.
We present the centrality dependence of the azimuthal angle correlation shapes between a trigger and associated charged hadrons in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV from the STAR experiment. The away-side structure is significantly modified in central collisions and is characterised in terms of a doubly-peaked yield. A minimum in the <$p_T$> of hadrons opposite to the trigger particle is also investigated.
We report the recent results of event anisotropy analysis focused on $v_2$ in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at PHENIX.
We present a measurement of the pseudorapidity density of primary charged particles near mid-rapidity in Au+Au collisions at sqrt(s_NN) = 130 GeV as a function of the number of participating nucleons. These results are compared to models in an attempt to discriminate between competing scenarios of particle production in heavy ion collisions.
We present preliminary results from D^0 meson measurements through the hadronic decay channel in minimum bias Au+Au collisions at \sqrt{s_{NN}} = 200 GeV at STAR. The measurements are performed using a secondary vertexing technique that exploits the resolution given by the Silicon detectors available in STAR.
We present preliminary results from a two-pion intensity interferometry analysis from Au+Au collisions at sqrt{s_{NN}}=200 GeV measured in the STAR detector at RHIC. The dependence of the apparent pion source on multiplicity and transverse momentum are discussed and compared with preliminary results from d+Au and p+p collisions at the same beam energy.
We investigate the squeezed back-to-back correlations (BBC) of $K^+$$K^-$, caused by the mass modification of the particle in the dense medium formed in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Au+Au collisions at $\sqrt{s_{NN}}=62.4$ GeV. Considering some kaons may be not affected by the medium, we further study the BBC functions of $K^+$$K^-$ when parts of all kaons have a mass-shift. Our results indicate that the BBC functions of $K^+$$K^-$ can be observed when only about 10$\%$ of all kaons have a mass-shift in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and the peripheral collisions …
In this paper, results on the J/$ψ$ cross section and polarization measured via the dielectron decay channel at mid-rapidity in $p+p$ collisions at $\sqrt{s}$ = 200 and 500 GeV in the STAR experiment are discussed. The first measurement of $ψ(2S)$ to J/$ψ$ ratio at $\sqrt{s}$ = 500 GeV is also reported.
We have measured the ratios of antiparticles to particles for charged pions, kaons and protons near mid-rapidity in central Au+Au collisions at sqrt(s_NN) = 130 GeV. For protons, we observe pbar/p = 0.60 +/- 0.04 (stat.) +/- 0.06 (syst.) in the transverse momentum range 0.15 < p_T < 1.0 GeV/c. This leads to an estimate of the baryo-chemical potential mu_B of 45 MeV, a factor of 5-6 smaller than in central Pb+Pb collisions at sqrt(s_NN) = 17.2 GeV.
In minimum bias (0-80%) Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, the elliptic flow ($v_{2}$) measurements for di-electrons from the low to intermediate mass region are presented. The differential elliptic flow as a function of transverse momentum in different mass regions are also reported. The simulated and measured $v_{2}$ of di-electrons are compared in the mass regions of $M_{ee}<0.14$ GeV/$c^{2}$ and $0.14<M_{ee}<0.3$ GeV/$c^{2}$.
Measurements of cross-sections and transverse single spin asymmetries of identified charged hadrons at forward rapidities from transversely polarized proton collisions at $\sqrt{s}$ = 200 GeV are presented. The results are discussed in the context of interplay between perturbative and non-perturbative QCD effects.
The production of dibaryons, light nuclei and hypertriton in the most central Au+Au collisions at $\sqrt{s_{NN}}=$ 11.5 and 200 GeV are investigated by using a naive coalescence model. The production of light nuclei is studied and found that the production rate reduces by a factor of 330 (1200) for each extra nucleon added to nuclei at $\sqrt{s_{NN}}=$ 11.5 (200) GeV. The $p_{T}$ integrated yield of multistrange hadrons falls exponentially as strangeness quantum number increases. We further investigate strangeness population factor $S_{3}, S_{2}$ as a function of transverse momentum as well as…
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…
In this proceeding, we present on our first measurements of identified particle ($π$, $K$, $p$, $K_{s}^{0}$, $Λ$, $ϕ$, $Ξ^{-}$) production and anisotropic flow ($v_{1}$, $v_{2}$) in Au+Au collisions at ${\sqrt{s_{\rm NN}} = \rm{3\,GeV}}$. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.
We predict the elliptic flow parameter v_2 in U+U collisions at sqrt{s_{NN}}=200 GeV and in Pb+Pb collisions at sqrt{s_{NN}} = 2.76 TeV using a hybrid model in which the evolution of the quark gluon plasma is described by ideal hydrodynamics with a state-of-the-art lattice QCD equation of state, and the subsequent hadronic stage by a hadron cascade model.
In hydrodynamical modeling of ultrarelativistic heavy-ion collisions, the freeze-out is typically assumed to take place at a surface of constant temperature or energy density. A more physical approach is to assume that freeze-out takes place at a surface of constant Knudsen number. We evaluate the Knudsen number as a ratio of the expansion rate of the system to the pion scattering rate, and apply the constant Knudsen number freeze-out criterion to ideal hydrodynamical description of heavy-ion collisions at RHIC ($\sqrt{s_\mathrm{NN}}=200$ GeV) and the LHC ($\sqrt{s_\mathrm{NN}}=2760$ GeV) ener…
We present the direct photon production for $1<p_{T}<10$ GeV/$c$ derived from continuum in the dielectron invariant mass region $0.1<M_{ee}<0.3$ GeV/$c^{2}$ from one billion $\sqrt{s_{NN}}=200$ GeV Au+Au events taken in year 2010 and 2011. A clear excess in the invariant yield compared to the number of binary collision scaled $p+p$ reference is observed in the \pt~range 1-4 GeV/$c$. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct photon invariant yield.
We report the direct virtual photon invariant yields in the transverse momentum ranges $1\!<\!p_{T}\!<\!3$ GeV/$c$ and $5\!<\!p_T\!<\!10$ GeV/$c$ at mid-rapidity derived from the dielectron invariant mass continuum region $0.10<M_{ee}<0.28$ GeV/$c^{2}$ for 0-80\% minimum-bias Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. A clear excess in the invariant yield compared to the number-of-binary-collisions ($N_{bin}$) scaled $p+p$ reference is observed in the $p_T$ range $1\!<\!p_{T}\!<\!3$ GeV/$c$. For $p_T\!>6$ GeV/$c$ the production follows $N_{bin}$ scaling. Model calculations with contributions…
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