J/psi production is considered to be a sensitive probe of the properties of quark gluon plasma created in nucleus+nucleus collisions at RHIC. In this article, the recent analysis of mid-rapidity (|y| < 1) J/psi production via the dielectron decay channel in Au+Au (year 2007) and Cu+Cu (year 2005) collisions at sqrt(sNN) = 200 GeV at STAR is reported. It is compared to STAR p+p results in order to study the nuclear modification factor as a function of transverse momentum and centrality. The results are compared to previously published data and available theoretical models.
Yields of prompt and non-prompt J/psi, as well as Y(1S) mesons, are measured by the CMS experiment via their dimuon decays in PbPb and pp collisions at sqrt(sNN) = 2.76 TeV for quarkonium rapidity |y|<2.4. Differential cross sections and nuclear modification factors are reported as functions of y and transverse momentum pt, as well as collision centrality. For prompt J/psi with relatively high pt (6.5<pt<30 GeV/c), a strong, centrality-dependent suppression is observed in PbPb collisions, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. In th…
In 2013, inclusive J/psi measurements in p-Pb collisions were performed at the LHC at sqrt(sNN) = 5.02 TeV, in order to measure the effects related to the cold nuclear matter on the J/psi production. Their evaluation is important in order to be able to disentangle hot and cold nuclear matter effects in Pb-Pb collisions. In this contribution, results on the inclusive J/psi production in p-Pb collisions, in the dimuon decay channel at forward and backward rapidity, down to zero transverse momentum, are presented and compared to theoretical models.
The Compact Muon Solenoid (CMS) is fully equipped to measure hard probes in the di-muon decay channel in the high multiplicity environment of nucleus-nucleus collisions. Such probes are especially relevant for studying the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. CMS has measured the nuclear modification factors of non-prompt J/psi (from b-hadron decays) and prompt J/psi in PbPb collisions at sqrt{s_{NN}} = 2.76 TeV. For prompt J/psi with relatively high p_T (p_T=6.5-30 GeV/c), a strong, centrality-dependent suppression …
The STAR collaboration at RHIC presents measurements of \Jpsi$\to{e^+e^-}$ at mid-rapidity and high transverse momentum ($p_T>5$ GeV/$c$) in \pp and central \cucu collisions at \sNN = 200 GeV. The inclusive \Jpsi production cross section for \cucu collisions is found to be consistent at high $p_T$ with the binary collision-scaled cross section for \pp collisions, in contrast to previous measurements at lower $p_T$, where a suppression of \Jpsi production is observed relative to the expectation from binary scaling. Azimuthal correlations of $J/ψ$ with charged hadrons in \pp collisions provide a…
Recent results indicate that the J/psi suppression pattern differs with rapidity showing a larger suppression at forward rapidity. J/psi suppression mechanisms based on energy density (such as color screening, interaction with co-movers, etc.) predict the opposite trend. On the other hand, it is expected that more c\bar{c} pairs should be available to form quarkonia at mid-rapidity via recombination. Some models provide a way to differentiate J/psi production from initially produced c\bar{c} pairs and final state recombination of uncorrelated pairs, via the rapidity and transverse momentum dep…
We present femtoscopic results for proton and Lambda correlation functions measured by ALICE in sqrt(sNN) = 2.76 TeV Pb-Pb collisions. Femtoscopic radii are extracted from pp, pbarpbar, and ppbar pairs. Comparisons of these radii with those from pion and kaon analyses reveal an approximate transverse mass scaling that is consistent with explanations of radial flow. Inelastic final state interactions are explored in baryon-antibaryon correlations functions to investigate their relationship with reduced proton yields at LHC energies.
The transverse momentum pT spectra of charged particles is measured by CMS as a function of collision centrality in PbPb collisions at sqrt(sNN) = 2.76 TeV. The results are compared to a pp reference spectrum, constructed by interpolation between sqrt(s) = 0.9 and 7 TeV measurements. The nuclear modification factor RAA is constructed by dividing the PbPb pT spectrum, normalized to the number of binary collisions (Ncoll), by the pp spectrum. Measured RAA in 0-5% centrality bin is compared to several theoretical predictions.
The transverse momentum spectra of charged particles have been measured in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV by the CMS experiment at the LHC. In the transverse momentum range pt = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 5 compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. At higher pt, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with pt in the range pt=40-100 GeV/c.
We report on the inclusive J/psi nuclear modification factor in p-Pb collisions at sqrt(s_NN) = 5.02 TeV as a function of rapidity y and transverse momentum p_T. The experimental coverage extends down to p_T = 0 GeV/c in the three rapidity ranges accessible by ALICE (-4.46 < y_cms < -2.96, -1.37 < y_cms < 0.46, 2.03 < y_cms < 3.53). The obtained results as a function of rapidity are in agreement with theory predictions based only on shadowing or on coherent energy loss. At forward and backward rapidity, the psi(2S) measurement complements the J/psi results. The ratio between the psi(2S) and J/…
The ratio between the prompt psi(2S) and J/psi yields, reconstructed via their decays into muon pairs, is measured in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC, corresponding to integrated luminosities of 150 inverse microbarns and 5.4 inverse picobarns, respectively. The double ratio of measured yields, (N[psi(2S)]/N[J/psi])[PbPb] / (N[psi(2S)]/ N[J/psi])[pp], is computed in three PbPb collision centrality bins and two kinematic ranges: one at midrapidity, abs(y) < 1.6, covering the transverse momentum range…
Charged particle transverse momentum (pT) spectra have been measured by CMS for pp and PbPb collisions at the same sqrt(sNN)=2.76 TeV collision energy per nucleon pairs. Calorimeter-based jet triggers are employed to enhance the statistical reach of the high-pT measurements. The nuclear modification factor (R_AA) is obtained in bins of collision centrality for the PbPb data sample dividing by the measured pp reference spectrum. In the range pT = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7. At higher pT, this suppression is sig…
ALICE is the dedicated heavy-ion experiment at the LHC. Due to the unique particle identification capabilities of the central barrel detectors (|eta|<0.9), J/psi can be measured in the di-electron channel in the very demanding environment of central Pb-Pb collisions at the LHC. In addition J/psi are measured at forward rapidity (2.5<y<4) with a dedicated muon spectrometer. ALICE is the only LHC experiment with an acceptance for J/psi that reaches down to p_T=0 at both, mid- and forward rapidity. Preliminary results on the nuclear modification factor of the inclusive J/psi production at mid- an…
Dijets in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV are studied with the CMS detector at the LHC. It is shown that the fragmentation functions of jets into charged particle tracks with transverse momenta pT > 4 GeV/c in PbPb collisions are similar to those in pp collisions, for both the leading and subleading jets. In addition, study of high statistics PbPb data acquired in 2011 shows that the quenching phenomenon exists up to highest jet pT values in excess of 300 GeV/c.
Isolated photon production is measured in pp and PbPb collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |eta|<1.44 and transverse energies E_T between 20 and 80 GeV with the CMS detector at the LHC. The measured E_T spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon E_T-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities.
Isolated photon production is measured in proton-proton and lead-lead collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80 GeV with the CMS detector at the LHC. The measured ET spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon ET-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities.
The STAR Collaboration reports measurements of differential jet shapes and semi-inclusive jet fragmentation functions in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=$ 200 GeV with the STAR detector at RHIC. Jet shapes, which represent the radial distribution of momentum carried by constituents, are measured differentially for (1) the charged particles transverse momentum and (2) the jet azimuthal angle relative to the second-order event plane. Based on the semi-inclusive population of jets recoiling from a high transverse momentum trigger hadron, jet fragmentation functions in 40-60% central h…
The first LHC measurement on ultra-peripheral heavy-ion collisions was carried out with the ALICE experiment. In this paper, ALICE results on exclusive J/psi studies in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, in the rapidity region -3.6 < y < -2.6, are given. The coherent J/psi cross section was found to be dsigma/dy_coh_J/ψ= 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst) mb. These studies favour theoretical models that include strong modifications to the nuclear gluon density, also known as nuclear gluon shadowing.
In the ALICE experiment, at forward rapidity (2.5 < y < 4), the production of heavy quarkonium states is measured via their mu+ mu- decay channels. We present the first measurement of inclusive J/Psi production, down to pT = 0, from Pb-Pb data collected at the LHC at sqrt(s_NN) = 2.76 TeV. Preliminary results on the nuclear modification factor (R_AA) and the central to peripheral nuclear modification factor (R_CP) show J/Psi suppression with no significant centrality dependence and an integrated R_AA(0-80%) = 0.49 \pm 0.03(stat.) \pm 0.11(syst.).
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities 2.2 < y < 2.2 in Au+Au collisions at sqrt(s_NN) = 200 GeV. The J/psi invariant yield and nuclear modification factor R_AA as a function of centrality, transverse momentum and rapidity are reported. A suppression of J/psi relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy J/Psi data at the Super Proton Synchrotron (SPS) invoking only J/psi destruction based on the local medium density would predict a significantly…
J/Psi production in p+p collisions at sqrt(s) = 200 GeV has been Measured in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) over a rapidity range of -2.2 < y < 2.2 and a transverse momentum range of 0 < pT < 9 GeV/c. The statistics available allow a detailed measurement of both the pT and rapidity distributions and are sufficient to constrain production models. The total cross section times branching ratio determined for J/Psi production is B_{ll} sigma_pp^J/psi = 178 +/- 3(stat) +/- 53(syst) +/- 18(norm) nb.
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…
J/psi production has been measured in proton-proton collisions at sqrt(s)= 200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at RHIC. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 3.99 +/- 0.61(stat) +/- 0.58(sys) +/- 0.40(abs) micro barns. The mean transverse momentum is 1.80 +/- 0.23(stat) +/- 0.16(sys) GeV/c.
Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodyna…
The relative modification of the prompt psi(2S) and J/psi yields from pp to PbPb collisions, at the center of mass energy of 5.02 TeV per nucleon pair, is presented. The analysis is based on pp and PbPb data samples collected by the CMS experiment at the LHC in 2015, corresponding to integrated luminosities of 28.0 inverse picobarns and 464 inverse microbarns, respectively. The double ratio of measured yields of prompt charmonia reconstructed through their decays into muon pairs, (N[psi(2S)]/N[J/psi])[PbPb] / (N[psi(2S)]/N[J/psi])[pp], is determined as a function of PbPb collision centrality a…
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.
In this paper, results on the J/psi cross section and polarization measured via the dielectron decay channel at mid-rapidity in p+p collisions at 200 and 500 GeV in the STAR experiment are discussed. Also, first measurements of the J/psi production as a function of the charged-particle multiplicity density and of psi(2S) to J/psi ratio at 500 GeV are reported.
First results are presented from J/Psi -> ee and J/Psi -> μμmeasurements by the PHENIX experiment at RHIC. These results are from a preliminary analysis of dielectrons from AuAu and pp data and dimuons from pp data measured in the RHIC run 2. A total cross section for J/Psi production in sqrt{s} = 200 GeV pp collisions of 3.8 \pm 0.6 (stat) \pm 1.3 (sys) microbarns is found. The J/Psi -> ee yield is presented versus number of binary collisions.
The nuclear modification factor RAA and the azimuthal anisotropy coefficient v[2] of prompt and nonprompt (i.e. those from decays of b hadrons) J/psi mesons, measured from PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta pt > 6.5 GeV/c and rapidity abs(y) < 2.4, extending down to pt = 3 GeV/c in the 1.6 < abs(y) < 2.4 range. The v[2] of prompt J/psi is found to be nonzero, but with no strong dependence on centrality, rapidity, or pt over the full kinem…
Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 inverse microbarns is analyzed. Jets are reconstructed using combined information from tracking and calorimetry. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the sa…
J/psi suppression induced by color screening of its constituent quarks was proposed 26 years ago as a signature of the formation of a quark gluon plasma in heavy-ion collisions. Recent results from ALICE in Pb-Pb collisions exhibit a smaller suppression with respect to previous measurements at the SPS and RHIC. The study of azimuthal anisotropy in particle production gives information on the collective hydrodynamic expansion at the early stage of the fireball, where the matter created in high-energy nuclear collisions is expected to be in a deconfined state. In particular, J/psi elliptic flow …
We analyze the relative azimuthal ($Δϕ$) distribution of same-charge and opposite-charge particle pairs. We then remove elliptic flow background using the ZYAM method. Comparisons between near angle $Δϕ$ peak widths are presented for various centralities.
The cross section for coherent J/psi photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, X[n]0[n], is measured with the CMS experiment in ultra-peripheral PbPb collisions at sqrt(s[NN]) = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 inverse microbarns, collected during the 2011 PbPb run. The J/psi mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dsigma[coh,X[n]0[n]] / d…
The measurements of charged-particle multiplicity and transverse energy at mid-rapidity in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV are reported as a function of centrality. The fraction of the inelastic cross section recorded by the ALICE detector is estimated using a Glauber model. The results scaled by the number of participating nucleons are compared with pp collisions at the same collision energy, to similar results obtained at significantly lower energies, and with models based on different mechanisms for particle production in nuclear collisions.
We report new quarkonia measurements necessary to understand production mechanisms and cold nuclear matter effects in the yields observed at RHIC energy. Results obtained in p+p collisions collected during the 2006 RHIC Run include J/psi, Psi' and Upsilon differential cross sections as well as J/psi polarization. Revisited interpretations of the published J/psi nuclear modification factors and statistically improved observations in d+Au collisions taken in the 2008 Run are also discussed in the view of the recent understanding of the initial state effects and breakup cross section.
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.
This poster presents the PHENIX results on high-p_T gamma-hadron and pi0-hadron correlations and shows the modification of away side jet shape by the medium. By comparing their jet shapes and yields, we see some evidence of the direct gamma contribution to correlation functions.
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 $\sqrt{s_\mathrm{NN}} = 17.4\mathrm{GeV}$.
Particle production of identified charged hadrons, $π^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ in Au+Au collisions at $\sqrt(snn) =$ 200 GeV has been studied as a function of transverse momentum and collision centrality at $y=0$ and $y\sim1$ by the BRAHMS experiment at RHIC. Significant collective transverse flow at kinetic freeze-out has been observed in the collisions. The magnitude of the flow rises with the collision centrality. Proton and kaon yields relative to the pion production increase strongly as the transverse momentum increases and also increase with centrality. Particle yields per p…
Inclusive transverse momentum distributions of charged hadrons within 0.2<pT<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt(sNN)=130 GeV. Hadron yields are suppressed at high pT in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high pT hadron production in heavy ion collisio…
The charged-particle pseudorapidity density dNch/deta has been measured for Au+Au collisions at sqrt(sNN)=130 GeV at RHIC, using the PHOBOS apparatus. The total number of charged particles produced for the 3% most central Au+Au collisions for |eta|<=5.4 is found to be 4200+-470. The evolution of dNch/deta with centrality is discussed, and compared to model calculations and to data from proton-induced collisions. The data show an enhancement in charged-particle production at mid-rapidity, while in the fragmentation regions, the results are consistent with expectations from pp and pA scattering.
This paper describes the measurement of elliptic flow for charged particles in Au+Au collisions at sqrt(sNN)=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used in order to reduce systematic uncertainties. The elliptic flow falls sharply with increasing eta at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at s…
Transverse momentum spectra of neutral pions in the range 0.7 < pT < 3.2 GeV/c have been measured at 2.3 < eta < 3.0 by the WA98 experiment in p+C and p+Pb collisions at sqrt(sNN) = 17.3 GeV. Scaled by the number of nucleon-nucleon collisions (Ncoll) the pi^0 yields in p+C and p+Pb at pT ~ 2.0 - 2.5 GeV/c are higher than the respective yields in central Pb+Pb collisions with Npart > 300. This observation is qualitatively consistent with expectations from parton energy loss.
This paper reports the measurement of J/psi meson production in proton-proton (pp) and proton-lead (pPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV by the CMS experiment at the LHC. The data samples used in the analysis correspond to integrated luminosities of 28 inverse picobarns and 35 inverse nanobarns for pp and pPb collisions, respectively. Prompt and nonprompt J/psi mesons, the latter produced from the decay of B mesons, are measured in their dimuon decay channels. Differential cross sections are measured in the transverse momentum range of 2 < pt < 30 GeV/c, and …
Transverse momentum spectra and rapidity densities, dN/dy, of protons, anti-protons, and net--protons (p-pbar) from central (0-5%) Au+Au collisions at sqrt(sNN) = 200 GeV were measured with the BRAHMS experiment within the rapidity range 0 < y < 3. The proton and anti-proton dN/dy decrease from mid-rapidity to y=3. The net-proton yield is roughly constant for y<1 at dN/dy~7, and increases to dN/dy~12 at y~3. The data show that collisions at this energy exhibit a high degree of transparency and that the linear scaling of rapidity loss with rapidity observed at lower energies is broken. The ener…
The balance function is a new observable based on the principle that charge is locally conserved when particles are pair produced. Balance functions have been measured for charged particle pairs and identified charged pion pairs in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV at the Relativistic Heavy Ion Collider using STAR. Balance functions for peripheral collisions have widths consistent with model predictions based on a superposition of nucleon-nucleon scattering. Widths in central collisions are smaller, consistent with trends predicted by models incorporating late hadronization.
We have measured the transverse momentum distributions of charged hadrons in d+Au collisions at sqrt sNN = 200 GeV in the range of 0.5 < p_T < 4.0 GeV/c. The total range of pseudorapidity, eta, is 0.2 < eta < 1.4, where positive eta is in the deuteron direction. The data has been divided into three regions of pseudorapidity, covering 0.2 < eta < 0.6, 0.6 < η< 1.0, and 1.0 < eta < 1.4 and has been compared to charged hadron spectra from p+pbar collisions at the same energy. There is a significant change in the spectral shape as a function of pseudorapidity. As eta increases we see a decrease in…
Charmonium is a prominent probe of the Quark-Gluon Plasma (QGP), expected to be formed in ultrarelativistic heavy-ion (A-A) collisions. It has been predicted that the J/psi(c-cbar) particle is dissolved in the deconfined medium created in A-A systems. However this suppression can be counterbalanced via regeneration of the charm/anti-charm bound state in QGP or via statistical production at the phase boundary. At LHC energies, the latter mechanisms are expected to play a more important role, due to a charm production cross section significantly larger than at lower energies. Measurements obtain…
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…
Yields of charged particles (pi+, pi-, K+, K-, p and p-bar) have been derived from spectra measured with BRAHMS for the reaction Au+Au at sqrt(sNN) = 200 GeV, as a function of rapidity in the range y = 0 to y ~ 3 for the 10% most central events. The yields peak at mid-rapidity with a small decrease in the range |y| < 1 but they drop significantly at higher rapidities except for the protons. At y = 0, the K-/pi- ratio is 0.18 +/- 0.02 (syst), very close to the K+/pi+ ratio equal to 0.19 +/- 0.02 (syst). But at y = 3, K-/pi- drops to 0.12 +/- 0.02 (syst) while K+/pi+ remains constant.
A Large Ion Collider Experiment (ALICE) is one of the four large experiments at the Large Hadron Collider (LHC), and it is dedicated to the study of ultra-relativistic heavy-ion collisions, with the goal of investigating the properties of the high-density state of QCD matter produced in these collisions. The study of D meson production azimuthal anisotropy and the measurement of their elliptic flow (v2) can provide insight on the degree of thermalisation of charm quarks in the medium and on the charm hadronization mechanism. We present the measurement of the D+ and D0 meson v2 in Pb-Pb collisi…
We report on the first measurement of inclusive J/$ψ$ elliptic flow, $v_2$, in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV in the rapidity range $2.5 < y < 4.0$. The dependence of the J/$ψ$ $v_2$ on the collision centrality and on the J/$ψ$ transverse momentum is studied in the range $0 < p_{\rm T} < 10$ GeV/$c$. For semi-central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, an indication of non-zero $v_2$ is observed with a maximum value of $v_2 = 0.116 \pm 0.046 {\rm (stat.)} \pm 0.029 {\rm …
The BRAHMS measured proton-to-pion ratios in Au+Au and p+p collisions at \rootsnn{62.4} and \rootsnn{200} are presented as a function of transverse momentum and collision centrality within the pseudo-rapidity range 0 < eta < 3.8 The results for Au+Au at sqrt(sNN) = 200 GeV are compared with predictions from models which incorporate hydro-dynamics, hadron rescattering and jet production, in the eta interval covered. In Au+Au collisions at sqrt(sNN) = 200 GeV, eta ~ 2.2, and at sqrt(sNN) = 62.4 GeV, eta = 0, the bulk medium can be characterized by the common value of \mi_B ~ 65 MeV. The p/pi rat…
We report on the rapidity and centrality dependence of proton and anti-proton transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as measured by the STAR experiment at RHIC. Our results are from the rapidity and transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons and anti-protons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y|<0.5. Comparisons of our…
We present the transverse momentum spectra at mid-rapidity for $d$, $\bar{d}$ ($1<p_{T}<4 GeV/c$) and $^{3}He$, $\bar{^{3}He}$ ($2<p_{T}<6 GeV/c$) measured by the STAR experiment at RHIC and extract the coalescence parameters $B_{2}$ and $B_{3}$ (respectively). We also present the $v_{2}$ measurement for $d(\bar{d})$ and $^{3}He(\bar{^{3}He})$. We find that the $d(\bar{d})$ and $p(\bar{p})$ $v_{2}$ follows the atomic mass number A scaling within errors and a negative $v_{2}$ has been observed for $\bar{d}$ at low $p_{T}$.
We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using the Colour-Singlet Model (CSM), including next-to-leading order (NLO) corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM reproduces the existing data if the upper range of the NNLO* is near the actual --but presently unknown-- NNLO. The direct yield polarisation for the NLO and NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger. Contrary to what is sometimes claimed in the literature, the prompt J/psi yield polarisation in the CSM is compatible with the experimental …
Two-particle correlations at small relative momenta give insight into the size of the emitting source. Of particular interest is the test of hydrodynamic models which predict a universal, apparent decrease of the extent of the system with increasing transverse mass mT as a consequence of the strong radial flow in heavy-ion collisions at LHC energies. This contribution presents a study of correlations for protons and Λ particles in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV measured with ALICE. The investigated particle species expand the experimental reach in mT due to their high rest mass. Resi…
Di-hadron correlation measurements have been used to probe di-jet production in collisions at RHIC. A strong suppression of the away-side high-pT yield in these measurements is direct evidence that high-pT partons lose energy as they traverse the strongly interacting medium. However, since the momentum of the trigger particle is not a good measure of the jet energy, azimuthal di-hadron correlations have limited sensitivity to the shape of the fragmentation function. We explore the possibility to better constrain the initial parton energy by using clusters of multiple high-pT hadrons in a narro…
The PHENIX experiment has shown that J/psis are suppressed in central Au+Au collisions at a center of mass energy per nucleon-nucleon collision sqrt s(NN) = 200 GeV, and that the suppression is larger at forward than at mid-rapidity. Part of this difference may be explained by cold nuclear matter effects but the most central collisions suggest that regeneration mechanisms could be at play. In 2007, PHENIX collected almost four times more Au+Au collisions at this energy than used for previous published results. Moreover, the addition of a new reaction plane detector allows a much better analysi…
Quarkonia states are expected to provide essential information on the properties of the high-density strongly-interacting system formed in the early stages of high-energy heavy-ion collisions. ALICE is the LHC experiment dedicated to the study of nucleus-nucleus collisions and can study charmonia at forward rapidity (2.5 < y < 4) via the mu+ mu- decay channel and at mid rapidity (|y| < 0.9) via the e+ e- decay channel. In both cases charmonia are measured down to zero transverse momentum. The inclusive J/psi production as a function of transverse momentum and rapidity in pp collisions at sqrt{…
Yields for J/psi production in Cu+Cu collisions at sqrt (s_NN)= 200 GeV have been measured by the PHENIX experiment over the rapidity range |y| < 2.2 at transverse momenta from 0 to beyond 5 GeV/c. The invariant yield is obtained as a function of rapidity, transverse momentum and collision centrality, and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data provide greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, providing a key constraint that is needed for disentangling c…
