We report on measurements of identified particle yields from Au-Au collisions at $\sqrt{s_{NN}} = 62.4$ GeV made with the BRAHMS spectrometer. Here we will concentrate on the charged $K/π$ ratios as function of rapidity and baryo-chemical potential. We find that the $K/π$ ratios measured at different rapidities in the analysed dataset have a common dependence with the same ratios measured in mid-rapidity at SPS energies when plotted as function of the $\bar{p}/p$ ratio. The theoretical models used for comparison, UrQMD and AMPT, give a reasonable description of the particle yields at mid-rapidity but fail to do so for the $K/π$ ratios at forward rapidity.
The production at central rapidity of K0s, Lambda, Xi and Omega particles in Pb-Pb collisions at 158 A GeV/c has been measured by the NA57 experiment over a centrality range corresponding to the most central 53% of the inelastic Pb-Pb cross section. In this paper we present the rapidity distribution of each particle in the central rapidity unit as a function of the event centrality. The distributions are analyzed based on hydrodynamical models of the collisions.
We have measured the rapidity distributions dN/dy of pi+/-, K+/- and p,pbar in central Au+Au collisions at sqrt(s_nn) = 200 GeV. The average rapidity loss per participant nucleon is 2.0 +/- 0.2 units of rapidity. The strange to non--strange meson ratios K/pi are found to track variations of the baryo--chemical potential in energy and rapidity.
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.
We present the measurement of the D+s production in pp collisions at sqrt{s} = 7 TeV and in Pb Pb collisions at sqrt{s_NN} =2.76 TeV performed with the ALICE detector at central rapidity through the reconstruction of the hadronic decay channel D+s-> K+K-pi+. The preliminary results of the D+s nuclear modification factor will be presented.
Transverse momentum spectra of protons and anti-protons measured in the rapidity range 0<y<3.1 from 0-10% central Au+Au collisions at sqrt{s_{NN}}=62.4 GeV are presented. The rapidity densities, dN/dy, of protons, anti-protons and net-protons N()p-N(pbar) have been deduced from the spectra over a rapidity range wide enough to observe the expected maximum net-baryon density. From mid-rapidity to y=1 the net-proton yield is roughly constant (dN/dy ~ 10),but rises to dN/dy ~25 at 2.3<y<3.1. The mean rapidity loss is 2.01 +-0.16 units from beam rapidity. The measured rapidity distributions are com…
The production at central rapidity of K0s, Lambda, Xi and Omega particles in Pb-Pb collisions at 158 A GeV/c has been measured by the NA57 experiment over a centrality range corresponding to the most central 53% of the inelastic Pb-Pb cross section. We present the rapidity distribution of each particle in the central rapidity unit. The distributions are analysed based on hydrodynamical models of the collisions.
We report on the J$ψ$ nuclear modification factor $R_{\rm AA}$ at mid-rapidity ($|y|<0.9$) in Pb-Pb collisions at $\sqrt{s_{NN}}=$2.76 TeV measured by ALICE. J$ψ$ candidates are reconstructed using their $e^+e^-$ decay channel. The kinematical coverage extends to zero transverse momentum allowing the measurement of integrated cross sections. We show the centrality dependence of the J$ψ$ $R_{\rm AA}$ at mid-rapidity compared to the results from PHENIX at mid-rapidity and ALICE results at forward-rapidity. We also discuss comparisons to calculations from theoretical models.
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 new results for the nuclear modification factor \RAA of \jpsi mesons as a function of centrality and transverse momentum at mid-rapidity. The measurement is carried out with the ALICE central barrel detectors in the acceptance range $|y|$ < 0.9 and \pt > 0 in the dielectron decay channel.
We report on preliminary identified particle ratios from Au+Au collisions at $\sqrt{s_{NN}} = 62.4$ GeV in different centrality classes, measured with the BRAHMS spectrometer. Results from Cu+Cu and p+p collisions at mid-rapidity at the same energy are also included. The average transverse momenta of particle spectra, anti-particle to particle ratios and $K/π$ ratios dependence on centrality and rapidity are shown and discussed.
The ratios of the yields of charged antiparticles to particles have been obtained for pions, kaons, and protons near mid-rapidity for d+Au collisions at sqrt(s_NN) = 200 GeV as a function of centrality. The reported values represent the ratio of the yields averaged over the rapidity range of 0.1<y_pi<1.3 and 0<y_(K,p)<0.8, where positive rapidity is in the deuteron direction, and for transverse momenta 0.1<p_(T)^(pi,K)<1.0 GeV/c and 0.3<p_(T)^(p)<1.0 GeV/c. Within the uncertainties, a lack of centrality dependence is observed in all three ratios. The data are compared to results from other sys…
Herewith we present the production of identified hadrons in Au+Au and p+p collisions at $\sqrt{s_{NN}}=200 {\rm GeV}$ at forward rapidity, $y \approx 3.2$. Suppression of pions and kaons and enhancement for protons in central Au+Au collisions is observed. These results are found to be very similar in strength to that observed at mid-rapidity. Furthermore, we see a gradual decrease of the observed suppression towards more peripheral collisions.
We report results on the ratio of mid-rapidity anti-proton to proton yields in Au+Au collisions at $\rts = 130$ GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of $|y|<0.5$ and 0.4 $<p_t<$ 1.0 GeV/$c$, the ratio is essentially independent of either transverse momentum or rapidity, with an average of $0.65\pm 0.01_{\rm (stat.)} \pm 0.07_{\rm (syst.)}$ for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the $p$-$\pb$ pair production becom…
We report the first measurement of strange ($Λ$) and anti-strange ($\barΛ$) baryon production from $\sqrt{s_{_{NN}}}=130$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at mid-rapidity are presented as a function of centrality. The yield of $Λ$ and $\barΛ$ hyperons is found to be approximately proportional to the number of negative hadrons. The production of $\barΛ$ hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic s…
We present first preliminary studies of $Λ$ and $\barΛ$ production in the pseudorapidity region $2.5 < |η| < 4$, covered by the forward radial-drift TPCs (FTPCs) in STAR. The FTPCs provide momentum and charge determination but no particle identification, making the use of combinatorial methods and background subtraction necessary for $Λ$ identification. The $\barΛ/Λ$ ratio measured at high rapidity is compared to the ratio obtained at mid-rapidity with the STAR TPC. Differences in the ratio at positive and negative rapidity point to an asymmetry in particle and antiparticle production in d+Au …
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…
Measurements of identified single particle distributions in d+Au collisions at \snn = 200 GeV at the RHIC collider are described. The dependence of these distributions on the centrality of the collisions, as well as the rapidity of the detected particles are emphasized in this report.
We present ratios of the numbers of charged antiparticles to particles (pions, kaons and protons) in Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV as a function of rapidity in the range $y$=0-3. While the particle ratios at midrapidity are approaching unity, the $K^-/K^+$ and $\bar{p}/p$ ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from $μ_B \approx 130$MeV at $y$=3 to $μ_B \approx 25$MeV at $y$=0.
The first measurement of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 2.76 TeV is presented. For an event sample corresponding to the most central 5% of the hadronic cross section the pseudo-rapidity density of primary charged particles at mid-rapidity is 1584 $\pm$ 4 (stat) $\pm$ 76 (sys.), which corresponds to 8.3 $\pm$ 0.4 (sys.) per participating nucleon pair. This represents an increase of about a factor 1.9 relative to pp collisions at similar collision energies, and about a factor 2.2 to c…
In this proceedings we present STAR measurements of two particle azimuthal correlations between trigger particles at mid-rapidity ($|η|<$ 1) and associated particles at forward rapidities (2.7 $<|η|<$ 3.9) in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}} $= 200 GeV. Two particle azimuthal correlations between a mid-rapidity trigger particle and forward-rapidity associated particles preferably probe large-x quarks scattered off small-x gluons in RHIC collisions. Comparison of the separate d- and Au-side measurements in d+Au collisions may potentially probe gluon saturation and the presence o…
We report on a study of the transverse momentum dependence of nuclear modification factors $R_{dAu}$ for charged hadrons produced in deuteron + gold collisions at $\sqrt{s_{NN}}= 200$GeV, as a function of collision centrality and of the pseudorapidity ($η= 0,1,2.2,3.2$) of the produced hadrons. We find significant and systematic decrease of $R_{dAu}$ with increasing rapidity. The midrapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturati…
We report on the first measurement of the azimuthal anisotropy ($v_2$) of dielectrons ($e^{+}e^{-}$ pairs) at mid-rapidity from $\sqrt{s_{_{NN}}} = 200$ GeV Au+Au collisions with the STAR detector at RHIC, presented as a function of transverse momentum ($p_T$) for different invariant-mass regions. In the mass region $M_{ee}\!<1.1$ GeV/$c^2$ the dielectron $v_2$ measurements are found to be consistent with expectations from $π^{0}$, $η$, $ω$ and $ϕ$ decay contributions. In the mass region $1.1\!<M_{ee}\!<2.9$ GeV/$c^2$, the measured dielectron $v_2$ is consistent, within experimental uncertaint…
Results are presented on hyperon and antihyperon production in Pb-Pb, pPb and pBe collisions at 158 GeV/c per nucleon. Lambda, Xi and Omega yields have been measured at central rapidity and medium transverse momentum as functions of the centrality of the collision. Comparing the yields in Pb-Pb to those in pBe interactions, strangeness enhancement is observed. The enhancement increases with the centrality and with the strangeness content of the hyperons, reaching a factor of about 20 for the Omega in the central Pb-Pb collisions.
Two-particle correlations of identical charged pion pairs from Au+Au collisions at sqrt(s_NN) = 200 GeV were measured by the PHOBOS experiment at RHIC. Data for the most central (0--15%) events were analyzed with Bertsch-Pratt (BP) and Yano-Koonin-Podgoretskii (YKP) parameterizations using pairs with rapidities of 0.4 < y < 1.3 and transverse momenta 0.1 < k_T < 1.4 GeV/c. The Bertsch-Pratt radii decrease as a function of pair transverse momentum. The pair rapidity Y_pipi roughly scales with the source rapidity Y_YKP, indicating strong dynamical correlations.
The centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor 2 from peripheral (70-80%) to central (0-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.
It is shown that in central collisions of $^{197}$Au nuclei with heavy emulsion nuclei at 11.6 $A$GeV/c two-particles pseudorapidity correlations for produced particles in terms of correlation functions demonstate predominantly long-range behaviour in contrast to nucleon-nucleon interactions. The experimental data are compared with calculations based on the FRITIOF-M model and the model of independent emission of particles.
We determine rapidity asymmetry in the production of charged pions, protons and anti-protons for large transverse momentum (pT) for d+Au collisions at \sqrt s_NN = 200 GeV. The identified hadrons are measured in the rapidity regions |y| < 0.5 and 0.5 < |y| < 1.0 for the pT range 2.5 < pT < 10 GeV/c. We observe significant rapidity asymmetry for charged pion and proton+anti-proton production in both rapidity regions. The asymmetry is larger for 0.5 < |y| < 1.0 than for |y|< 0.5 and is almost independent of particle type. The measurements are compared to various model predictions employing multi…
Measurements, with the BRAHMS detector, of the antiproton to proton ratio at central and forward rapidities are presented for Au+Au reactions at sqrt{s_{NN}}=130 GeV, and for three different collision centralities. For collisions in the 0-40% centrality range we find $N(\bar{\rm p})/N({\rm p}) = 0.64 +- 0.04 (stat.) +- 0.06 (syst.) at y ~0, 0.66 +- 0.03 +- 0.06 at y ~ 0.7, and 0.41 +- 0.04 +- 0.06 at y ~ 2. The ratios are found to be nearly independent of collision centrality and transverse momentum. The measurements demonstrate that the antiproton and proton rapidity densities vary differentl…
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.
Two-particle correlations of identical charged pion pairs from Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV were measured by the PHOBOS experiment at RHIC. Data for the 15% most central events were analyzed with Bertsch-Pratt and Yano-Koonin-Podgoretskii parameterizations using pairs with rapidities of 0.4 < y_{ππ} < 1.3 and transverse momenta 0.1 < k_T < 1.4 GeV/c. The Bertsch-Pratt radii R_o and R_l decrease as a function of pair transverse momentum, while R_s is consistent with a weaker dependence. R_o and R_s are independent of collision energy, while R_l shows a slight increase. The …
We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($η=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $η=2.2$ exhibit suppression for charged pions but not for (anti-)protons at intermediate $p_T$. The $\bar{p}/π^-$ ratios have been measured up to $p_T\sim 3$ GeV/$c$ at the two …
Results are presented on neutral kaon, hyperon and antihyperon production in Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern follows the same hierarchy as seen in the higher energy data - the enhancement increases with the strangeness content of the hyperons and with the centrality of collision. The centrality dependence of the Pb-Pb yields and enhancements is steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness enhancements at mid-rapidity is discussed.
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…
We have measured rapidity densities dN/dy of pions and kaons over a broad rapidity range (-0.1 < y < 3.5) for central Au+Au collisions at sqrt(snn) = 200 GeV. These data have significant implications for the chemistry and dynamics of the dense system that is initially created in the collisions. The full phase-space yields are 1660 +/- 15 +/- 133 (pi+), 1683 +/- 16 +/- 135 (pi-), 286 +/- 5 +/- 23 (K+) and 242 +/- 4 +/- 19 (K-). The systematics of the strange to non--strange meson ratios are found to track the variation of the baryo-chemical potential with rapidity and energy. Landau--Carruthers…
We report STAR results on the azimuthal anisotropy parameter v2 for strange particles K0S and Lambda at midrapidity in Au+Au collisions at /s_NN = 130 GeV at RHIC. The value of v2 as a function of transverse momentum pt and collision centrality is presented for both particles and compared to model calculations. A strong pt dependence in v2 is observed up to pt ~2.0 GeV/c where v2 begins to saturate.
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 five 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.
We present results on inclusive electrons for 1.5 $ < p_{\rm T} < $ 6 GeV/$c$ in {Pb-Pb} collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV measured with ALICE at the LHC and compare these to a cocktail of background electron sources. The excess of electrons beyond the cocktail at high momenta ({$p_{\rm T} >$ 3.5 GeV/$c$}) is attributed to electrons from heavy-flavour decays. The corresponding nuclear modification factor indicates heavy-flavour suppression by a factor of 1.5-4.
We report on the measurement of the inclusive $Υ$(1S) production in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV carried out at forward rapidity ($2.5<y<4$) and down to zero transverse momentum using its $μ^{+}μ^{-}$ decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive $Υ$(1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon-nucleon collisions. The nuclear modification factor, for events in the 0-90$\%$ centrality range, amounts to $0.30\pm0.05{\rm (stat)}\pm0.04{\rm (syst)}$. The observed $Υ$(1…
We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at mid-rapidity in deuteron-gold (d+Au) and proton-proton (p+p) collisions at sqrt(s_NN) = 200 GeV. Jet structures are observed in the correlations which we quantify in terms of the conditional yield and angular width of away side partners. The kinematic region studied here samples partons in the gold nucleus carrying nucleon momentum fraction x~0.1 to x~0.01. Within this range, we find no x dependence of the jet structure in d+Au colli…
We briefly discuss the methods of analysing reconstructed neutral strange particles in p+p collision data measured at sqrt(s) = 200 GeV taken using the Solenoidal Tracker At RHIC (STAR) detector. We present spectra for K0 short, lambda and anti-lambda as a function of pT and multiplicity, and compare to previous high energy p+pbar collision data. The two component nature of the spectra suggests contributions from hard and soft processes, and the observed increase of mean pT with multiplicity indicates a growing contribution from the hard processes. The work described herein was presented as a …
The directed flow of charged particles at mid-rapidity is measured in Pb-Pb collisions at $\sqrt{s_\rm{NN}}=2.76$ TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be indep…
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…
The PHENIX experiment at RHIC has measured transverse energy and charged particle multiplicity at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments, and experiments at lower energies. The $\sqrt{s_{NN}}$ dependence of $dE_{T}/dη$ and $dN_{ch}/dη$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE_{T}/dη$ and $dN_{ch}/dη$ is similar at all measured incident energies. At RHIC energi…
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…
The PHOBOS experiment has measured the charged particle multiplicity at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of the collision centrality. Results on dN/deta(eta<1) divided by the number of participating nucleon pairs, <Npart/2>, are presented as a function of <Npart>. As was found from similar data at sqrt(s_NN) = 130 GeV, the data can be equally well described by parton saturation models and two-component fits which include contributions that scale as Npart and the number of binary collisions, Ncoll. We compare the data at the two energies by means of the rat…
Mid-rapidity azimuthal correlations probe di-jets originating mainly from gluon-gluon hard-scattering. Measurements of such correlations have revealed significant (gluon-)jet modification in central Au+Au collisions. Azimuthal correlations at forward rapidity with a mid-rapidity high-pt hadron, on the other hand, are sensitive primarily to quark-gluon hard-scattering and may probe quark-jet modification in nuclear medium. They may be also sensitive to the Color Glass Condensate by separating d-side and Au-side in d+Au collisions. We present the first results on correlations of charged hadrons …
New data on Lambda production in Au+Au collisions at 11.5 A GeV/c are presented. The measurements cover the rapidity range from y=2.0 to 3.5 and transverse momenta from pt=0.15 GeV/c to 1.5 GeV/c. The rapidity distributions, transverse momentum spectra, and azimuthal distributions are presented for different centralities of the collision. A strong positive directed flow at forward rapidity is observed for semicentral collisions. The measured spectra, yields and directed flow are compared with the predictions of RQMD v2.3 model.
Values of the ratios in the mid-rapidity yields of anti-Lambda/Lambda = 0.71 +/- 0.01(stat.) +/- 0.04(sys.), anti-Xi+/Xi- = 0.83 +/- 0.04(stat.) +/- 0.05 (sys.), anti-Omega+/Omega- = 0.95 +/- 0.15(stat) +/- 0.05(sys.) and K+/K- 1.092 +/- 0.023(combined) were obtained in central sqrt(s_NN) = 130 GeV Au+Au collisions using the STAR detector. The ratios indicate that a fraction of the net-baryon number from the initial system is present in the excess of hyperons over anti-hyperons at mid-rapidity. The trend in the progression of the baryon ratios, with increasing strange quark content, is similar…
The PHENIX experiment at RHIC has measured transverse energy and charged particle multiplicity at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments, and experiments at lower energies. The sqrt(s_NN) dependence of dE_T/deta and dN_ch/deta per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of dE_T/deta and dN_ch/deta is similar at all measured incident energies. At RHIC energies the ratio of transverse…
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…
The ALICE collaboration has studied inclusive J/$ψ$ and $ψ$(2S) production at forward rapidities in pp collisions at $\sqrt{s} = 7$ TeV with the ALICE Muon Spectrometer. The analysis has been carried out on a data sample corresponding to an integrated luminosity $\mathcal{L}_{\rm int}$ = 1.35 pb$^{-1}$. The production cross-sections of J/$ψ$ and $ψ$(2S), integrated over \pt\ (0 $<$ \pt\ $<$ 20 GeV/$c$) and \y\ (2.5 $<$ \y\ $<$ 4), have been measured. The J/$ψ$ and $ψ$(2S) differential cross-sections, in transverse momentum and rapidity, have also been measured. The results have been compared w…
Identified particle elliptic flow results are presented for the Au+Au reaction at sqrt[s_{NN}] = 200$ GeV as a function of transverse momentum and pseudorapidity. Data at pseudorapidities eta approximately equal to 0, 1, and 3.4 were obtained using the two BRAHMS spectrometers. Differential v2(eta, pt) values for a given particle type are found to be essentially constant over the covered pseudorapidity range, in contrast to the integral v2 values which have previously been observed to decrease at forward rapidities. A softening of the particle spectra at forward angles is found to account for …
Results are presented on $π^\pm$, $K^\pm$, and $\bar{p}$ transverse mass spectra and particle multiplicity ratios at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$=130 and 200 GeV and in p+p collisions at $\sqrt{s}$=200 GeV. Comparisons are made to results from lower energies. The bulk properties of the collision inferred from these results are discussed.
The production of muons from heavy flavour decays is measured at forward rapidity (2.5 < y < 4) with the muon spectrometer of the ALICE experiment at the LHC. In pp collisions at \sqrt{s} = 7 TeV, the measurement of the transverse momentum and rapidity differential production cross section of muons from heavy flavour decays is carried out from a data sample corresponding to an integrated luminosity of Lint = 16.5 nb^-1 and results are compared to predictions based on perturbative QCD calculations. In Pb-Pb collisions at \sqrt{s_{NN}}= 2.76 TeV, the analysis of a data sample corresponding to an…
A strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on how this state is formed and can be studied by measuring the pseudorapidity and transverse momentum dependence of the second Fourier component ($v_{2}(p_{T})$) of the azimuthal angular distribution. We report on a measurement of identified-particle $v_{2}$ as a function of $p_{T}$ (0.5-2.0 GeV/c), centrality (0-25%, 25-50%), and pseudorapidity ($0\leqη<3.2$) for $\sqrt{s_{NN}} = 200 \rm GeV$ Au+Au collisions. The BRAHMS …
Using the forward time projection chambers of the STAR experiment at the Brookhaven Relativistic Heavy Ion Collider we measure the centrality dependent Lambda and Anti-Lambda yields and inverse slope parameters in d+Au collisions at forward and backward rapidities y = +- 2.75. The contributions of different processes to stopping and baryon transport are probed exploiting the inherent asymmetry of the d+Au system. Comparisons to model calculations show that the baryon transport on the deuteron side is due to multiple collisions of the deuteron nucleons with gold participants. On the gold side, …
Mid-rapidity azimuthal correlations probe di-jets originating mainly from gluon-gluon hard-scattering. Measurements of such correlations have revealed significant (gluon-)jet modification in central Au+Au collisions. Azimuthal correlations of hadrons at forward rapidity with a mid-rapidity high-$\pt$ hadron, on the other hand, probe asymmetric partonic scatterings involving large-x quarks and small-x gluons. We present preliminary results from STAR on correlations of charged hadrons at forward rapidity in the forward TPCs ($2.7<|η|<3.9$, $\pt<2$ GeV/$c$) with high-$\pt$ charged hadrons at mid-…
Invariant pT spectra and rapidity densities covering a large rapidity range(-0.1 < y < 3.5) are presented for $π^{\pm}$ and $K^{\pm}$ mesons from central Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 GeV. The mid-rapidity yields of meson particles relative to their anti-particles are found to be close to unity ($π^-/π^+ \sim 1$, $K^-/K^+ \sim 0.85$) while the anti-proton to proton ratio is $\bar{p}/p \sim 0.49$. The rapidity dependence of the $π^-/π^+$ ratio is consistent with a small increase towards forward rapidities while the $K^-/K^+$ and $\bar{p}/p$ ratios show a steep decrease to $\sim$ 0.…
Two-proton and two-deuteron correlations have been studied in the target fragmentation region of central Pb+Pb collisions at 158 A GeV. Protons and deuterons were measured with the Plastic Ball spectrometer of the WA98 experiment at the CERN SPS. The results of one-dimensional and multi-dimensional analyses using both the Bertsch-Pratt and Yano-Koonin-Podgoretsky parameterizations of the two-particle correlation functions are presented. The proton source exhibits a volume emission, while the deuteron source, with small outward radius, appears opaque. Both proton and deuteron sources have cross…
