We report $J/ψ$ spectra for transverse momenta $p_T$> 5 GeV/$c$ at mid-rapidity in p+p and Au+Au collisions at sqrt(s_{NN}) = 200 GeV.The inclusive $J/ψ$ spectrum and the extracted $B$-hadron feed-down are compared to models incorporating different production mechanisms. We observe significant suppression of the $J/ψ$ yields for $p_T$> 5 GeV/$c$ in 0-30% Au+Au collisions relative to the p+p yield scaled by the number of binary nucleon-nucleon collisions in Au+Au collisions. In 30-60% collisions, no such suppression is observed.The level of suppression is consistently less than that of high-$p_T$ $π^{\pm}$ and low-$p_T$ $J/ψ$.
We evaluate $n$-particle ($n=2,3,4,5$) transverse momentum correlations for pions and kaons following from the decay of statistical clusters. These correlation functions could provide strong constraints on a possible existence of thermal clusters in the process of particle production.
Transverse momentum spectra of particles produced in high energy collisions are very important due to their relations to the excitation degree of interacting system. To describe the transverse momentum spectra, one can use more than one probability density functions of transverse momenta, which are simply called the functions or distributions of transverse momenta in some cases. In this paper, a few distributions of transverse momenta in high energy collisions are compared with each other in terms of plots to show some quantitative differences. Meanwhile, in the framework of Tsallis statistics…
We report the transverse momentum (pT) distributions for identified charged pions, protons and anti-protons using events triggered by high deposit energy in the Barrel Electro-Magnetic Calorimeter (BEMC) from p + p collisions at psNN = 200 GeV. The spectra are measured around mid-rapidity (|y|<0.5) over the range of 3<pT<15 GeV/c with particle identification (PID) by the relativistic ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) in the Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton spectra at high pT are compared with published results from m…
The PHOBOS experiment at RHIC has the unique capability of measuring particle production at very low transverse momenta. New results on low-transverse momentum invariant yields of pions, kaons, protons and antiprotons in 200 GeV Au+Au collisions are presented as a function of the collision centrality for the 50% most central events. In contrast to the results from d+Au collisions, no $m_{T}$ scaling is observed in the very low $p_{T}$ region. The low transverse momentum yields agree with extrapolations from intermediate transverse momentum measurements. For all collision centralities a flatten…
We present results on charged particle production at very low transverse momenta in the 15% most central Au+Au collisions at sqrt(s_NN) = 200 GeV obtained with the PHOBOS detector at RHIC. The invariant yields were measured at mid-rapidity in the transverse momentum ranges from 30 to 50 MeV/c for charged pions, 90 to 130 MeV/c for charged kaons and 140 to 210 MeV/c for protons and antiprotons. No significant enhancement in low transverse momentum particle production is observed as compared to extrapolations of identified particle spectra measured at an intermediate pT range. The spectra tend t…
The azimuthal anisotropy of charged particles in PbPb collisions at nucleon-nucleon center-of-mass energy of 2.76 TeV is measured with the CMS detector at the LHC over an extended transverse momentum (pt) range up to approximately 60 GeV. The data cover both the low-pt region associated with hydrodynamic flow phenomena and the high-pt region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v2) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the …
The transverse momentum spectra of identified charged particles have been measured at very low and intermediate transverse momenta in Au+Au collisions at sqrt(s_NN) = 62.4 GeV and d+Au collisions at sqrt(s_NN) = 200 GeV using the PHOBOS detector at RHIC. New results on charged particle production at very low p_T in central Au+Au collisions at sqrt(s_{NN) = 200 GeV in the centrality intervals 0-6% and 6-15% are presented. A comparison of the PHOBOS low-p_T data with predictions of a recent optical model is shown. The shapes of m_T spectra for d+Au and Au+Au collisions are compared.
The ALICE experiment has unique capabilities for particle identification at mid rapidity over a wide range of transverse momenta, making it an ideal tool for comprehensive measurements of hadrons such as charged pions, kaons, and protons as well as lambdas, K0s, and phi. The transverse momentum distributions and nuclear modification factors, R_pPb and R_PbPb, of these hadrons measured in p-Pb and Pb-Pb collisions are presented. Baryon-to-meson ratios exhibit a multiplicity-dependent enhancement at intermediate transverse momenta for both p-Pb and Pb-Pb collisions, while no significant dynamics…
The precise reconstruction of jet transverse momenta in heavy-ion collisions is a challenging task. A major obstacle is the large number of uncorrelated (mainly) low-$p_\mathrm{T}$ particles overlaying the jets. Strong region-to-region fluctuations of this background complicate the jet measurement and lead to significant uncertainties. We developed a novel approach to correct jet momenta (or energies) for the underlying background in heavy-ion collisions. The approach allows the measurement of jets down to extremely low transverse momenta and for large resolution $R$ by making use of common Ma…
Transverse momentum spectra of $π^{\pm}$, $\rm K^{\pm}$ and p($\bar{\rm p}$) up to $p_{\rm T}$ = 20 GeV/$c$ at mid-rapidity in pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at $p_{\rm T} \approx 3 GeV/c$ in central Pb-Pb collisions. Below the peak, $p_{\rm T}$ < 3 GeV/$c$, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadron…
Differential measurements of various particle species over an extended momentum range provide a sensitive experimental tool for investigation of energy loss mechanisms in the medium created in nucleus-nucleus collisions at RHIC. In these proceedings, a systematic study of transverse momentum spectra for charged pions, protons and antiprotons from Cu+Cu data at $\sqrt{s_{NN}}=200$GeV as a function of collision centrality will be presented. Such systematic studies provide additional insights into the interplay between fragmentation and non-fragmentation contributions to the particle production. …
The collective harmonic flow in heavy-ion collisions correlates particles at all transverse momenta to be emitted preferably some directions. The factorization breaking coefficient measures the small decorrelation of the flow harmonics at two different transverse momenta. Using the hydrodynamic model I study in details the decorrelation of the harmonic flow due to the flow angle and the flow magnitude decorrelation at two transverse momenta. The effect can be seen in experiment measuring factorization breaking coefficients for the square of the harmonic flow vector at two transverse momenta. T…
Forward-backward (FB) correlations are considered to be a powerful tool for the exploration of the early dynamics of hadronic interactions. The FB correlation functions can be constructed from different observables calculated event-by-event in two separated pseudorapidity regions. We report measurements of event-by-event average transverse momentum correlations for charged particles in two separated pseudorapidity regions in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ and 5.02 TeV recorded with ALICE at the LHC. The event-by-event mean transverse momenta correlations are robust against volume…
The transverse structure of jets was studied via jet fragmentation transverse momentum ($j_{\rm{T}}$) distributions, obtained using two-particle correlations in proton-proton and proton-lead collisions, measured with the ALICE experiment at the LHC. The highest transverse momentum particle in each event is used as the trigger particle and the region $3 < p_{\rm{Tt}} < 15$ GeV/$c$ is explored in this study. The measured distributions show a clear narrow Gaussian component and a wide non-Gaussian one. Based on Pythia simulations, the narrow component can be related to non-perturbative hadronizat…
The first measurement of energy produced transverse to the beam direction at RHIC is presented. The mid-rapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that E_T / N_ch remains relatively constant as a function of centrality. The energy density calculated via Bjorken's prescription for the 2% most central Au+Au collisions at sqrt(s_NN)=130 GeV is at least epsilon_Bj = 4.6 GeV/fm^3 which is a factor of 1.6 larger than found at sqrt(s_NN)=17.2 GeV (Pb+Pb at CERN).
We report transverse momentum ($p_{T} \leq15$ GeV/$c$) spectra of $π^{\pm}$, $K^{\pm}$, $p$, $\bar{p}$, $K_{S}^{0}$, and $ρ^{0}$ at mid-rapidity in p+p and Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. Perturbative QCD calculations are consistent with $π^{\pm}$ spectra in p+p collisions but do not reproduce $K$ and $p(\bar{p})$ spectra. The observed decreasing antiparticle-to-particle ratios with increasing $p_T$ provide experimental evidence for varying quark and gluon jet contributions to high-$p_T$ hadron yields. The relative hadron abundances in Au+Au at $p_{T}{}^{>}_{\sim}8$ GeV/$c$ a…
Data from the Large Hadron Collider on elliptic flow correlations at low and high $p_T$ from Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$~TeV are analyzed and interpreted in the framework of the HYDJET++ model. This model allows us to describe simultaneously the region of both low and high transverse momenta and, therefore, to reproduce the experimentally observed nontrivial centrality dependence of elliptic flow correlations. The origin of the correlations between low and high-$p_T$ flow components in peripheral lead-lead collisions is traced to correlations of particles in jets.
We present transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt(s_NN) = 200 GeV. The evolution of the spectra for transverse momenta p_T from 0.25 to 5GeV/c is studied as a function of collision centrality over a range from 65 to 344 participating nucleons. We find a significant change of the spectral shape between proton-antiproton and peripheral Au+Au collisions. Comparing peripheral to central Au+Au collisions, we find that the yields at the highest p_T exhibit approximate scaling with the number of participating nucleons, rather than scaling with the nu…
Transverse momentum ($p_{\mathrm{T}}$) distributions of identified hadrons produced in p-Pb collisions at $\mathrm{\sqrt{s_{NN}} = 5.02\ TeV}$ have been measured at mid-rapidity (0 $< y_{\mathrm{CMS}} <$ 0.5) by ALICE. Particle tracks are reconstructed using the central barrel detectors. Particle identification is performed via specific energy loss, time-of-flight or their characteristic decay topology over a wide transverse momentum range (0 GeV/c up to 8 GeV/c). Spectral shapes and particle ratios are measured in six multiplicity classes. They are compared with several model calculations and…
The two-particle differential transverse momentum correlator $G_{2}$ recently measured in Pb$-$Pb collisions, emerged as a powerful tool to gain insight into particle production mechanisms and to infer transport properties such as the ratio of shear viscosity to entropy density of the medium created in Pb$-$Pb collisions. In this poster, recent ALICE measurements of this correlator in pp collisions at $\sqrt{s}=7$ and p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV are presented to search, in particular, for viscous effects expected to arise in fluid-like systems produced in these collisions…
Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au+Au collisions at $\sqrt{s_{_{NN}}}$= 200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au+Au collisions to those in $p+p$ at the same energy. Elliptic anisotropy, $v_2$, is found to reach its maximum at $p_t \sim 3$ GeV/c, then decrease slowly and remain significant up to $p_t\approx 7$ -- 10 GeV/c. Stronger suppression is found in the back-to-back high-$p_t$ particle correlations for particles emitted out-of…
The transverse energy ET in PbPb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy sqrt(s[NN]) has been measured over a broad range of pseudorapidity eta and collision centrality using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity d(ET)/d(eta) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse e…
Low transverse momentum direct photon measurements have been carried out by the ALICE experiment at the CERN LHC in small collision systems (pp, $\sqrt{s}=2.76$ and 8 TeV and p--Pb, $\sqrt{s_\text{NN}}=5.02$ TeV) as well as in heavy-ion collisions (Pb--Pb, $\sqrt{s_\text{NN}}=2.76$ TeV). For the first time, also the multiplicity dependence of direct photon production was investigated in p--Pb collisions. Whereas in the small systems no significant thermal photon signal was observed, a $\sim15\%$ excess has been measured in central Pb--Pb collisions in the region of $p_{\rm T}<3$ GeV/$c$. A sig…
Transverse momentum spectra of $π^{\pm}$, $p$ and $\bar{p}$ up to 12 GeV/c at mid-rapidity in centrality selected Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV are presented. In central Au+Au collisions, both $π^{\pm}$ and $p(\bar{p})$ show significant suppression with respect to binary scaling at $p_T > $ 4 GeV/c. Protons and anti-protons are less suppressed than $π^{\pm}$, in the range 1.5 $< p_{T} <$6 GeV/c. The $π^-/π^+$ and $\bar{p}/p$ ratios show at most a weak $p_T$ dependence and no significant centrality dependence. The $p/π$ ratios in central Au+Au collisions approach the values i…
Measurements of various particle species over an extended momentum range provide a sensitive experimental tool for investigating particle production mechanisms in hadronic collisions. Comparison of the spectral shapes from different collision centralities measured with the STAR detector at RHIC allows one to study the interplay of soft and hard particle production for mesons and investigate various baryon-meson effects. Systematic studies of identified particle spectra for various colliding systems and different incident energies provide additional insights toward the interplay between fragmen…
The results on the the vector $A_y$, $A_{yy}$ and $A_{xx}$ analyzing powers in deuteron-proton elastic scattering at large scattering angles are presented. These data were obtained at internal target at JINR Nuclotron in the energy range 400-1800 MeV using polarized deuteron beam from new polarized ion source. New data on the deuteron analyzing powers in the wide energy range demonstrate the sensitivity to the short-range spin structure of the isoscalar nucleon-nucleon correlations.
Using a covariant coalescence model, we study hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons in minijets. Including transverse flow of soft partons and independent fragmentation of minijet partons, the model is able to describe available experimental data on pion, kaon, and antiproton spectra. The resulting antiproton to pion ratio is seen to increase at low transverse momenta and reaches a value of about one at intermediate transverse momenta, as observed in experimental data at RHIC. A similar dependence of the antikao…
In this paper, the experimental (simulated) transverse momentum spectra of negatively charged pions produced at mid-rapidity in central nucleus-nucleus collisions at the Heavy Ion Synchrotron (SIS), Relativistic Heavy Ion Collider (RHIC), and Large Hadron Collider (LHC) energies obtained by different collaborations are selected by us to investigate, where a few simulated data are taken from the results of FOPI Collaboration who uses the IQMD transport code based on Quantum Molecular Dynamics. A two-component standard distribution and the Tsallis form of standard distribution are used to fit th…
We report measurements of the ratios of identified hadrons (pi,K,p,Lambda) in Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of both collision centrality and transverse momentum (p_T). Ratios of anti-baryon to baryon yields are independent of p_T within 2<p_T <6 GeV/c indicating that, for such a range, our measurements are inconsistent with theoretical pQCD calculations predicting a decrease due to a stronger contribution from valence quark scattering. For both strange and non-strange species, a strong baryon enhancement relative to meson yields is observed as a function of collision c…
The PHENIX experiment at RHIC has measured the invariant cross section for omega-meson production at mid-rapidity in the transverse momentum range 2.5 < p_T < 9.25 GeV/c in p+p and d+Au collisions at sqrt(s_NN) = 200 GeV. Measurements in two decay channels (omega --> pi^0 pi^+ pi^- and omega --> pi^0 gamma) yield consistent results, and the reconstructed omega mass agrees with the accepted value within the p_T range of the measurements. The omega/pi^0 ratio is found to be 0.85 +/- 0.05(stat) +/- 0.09(sys) and 0.94 +/- 0.08(stat) +/- 0.12(sys) in p+p and d+Au collisions respectively, independen…
The description of the hadron production at very forward rapidities and low transverse momentum is usually made using phenomenological models based on nonperturbative physics. However, at high energies and large rapidities the wave function of one of the projectiles is probed at very small Bjorken $x$, being characterized by a large number of gluons. In this kinematical regime, a new state of matter - the Color Glass Condensate (CGC) - is expected to be formed. One the main characteristics of such system is the presence of a new dynamical momentum scale, the saturation scale $Q_s$, which can a…
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.
Although transverse-mass scaling of femtoscopic radii is found to hold to a good approximation in heavy-ion collision experiments, it is seen to fail for high-energy proton-proton collisions. It is shown that if invariant radius parameters are plotted versus the transverse velocity instead, scaling with the transverse velocity is seen in $\sqrt{s}=7$ TeV proton-proton experiments. A simple semi-classical model is shown to qualitatively reproduce this transverse velocity scaling.
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 report new results on identified (anti)proton and charged pion spectra at large transverse momenta (3<$p_{T}$<10 GeV/c) from Cu+Cu collisions at $\sqrt{s_{NN}}$=200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). This study explores the system size dependence of two novel features observed at RHIC with heavy ions: the hadron suppression at high-$p_{T}$ and the anomalous baryon to meson enhancement at intermediate transverse momenta. Both phenomena could be attributed to the creation of a new form of QCD matter. The results presented here bridge the system size gap…
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.
Using the coalescence model based on the phase-space distribution of nucleons from an extended blast-wave model that includes the space-momentum correlation of high momentum nucleons, we study the transverse momentum spectra and elliptic flows of deuteron and helium-3 in Pb+Pb collisions at the energy $\sqrt{s_{NN}}=2.76$ TeV. We find that the measured elliptic flows of deuteron can be satisfactorily described if nucleons of large transverse momenta are more spread in space when their momenta are more aligned along the reaction plane.
The transverse momentum and pseudorapidity distributions of final-state particles produced in proton-lead (p-Pb) collisions at center-of-mass energy per nucleon pair \sqrt{s_{NN}}=5.02 TeV are studied in the framework of a multisource thermal model. Experimental results measured by the ALICE and CMS Collaborations are described by the Tsallis transverse momentum distribution and the two-cylinder pseudorapidity distribution. Based on the parameter values extracted from the transverse momentum and pseudorapidity distributions, some other quantities are extracted. Then, the structure pictures of …
Transverse momentum spectra up to 4.5 GeV/c around midrapidity of pi^{+/-}, p, pbar, K^{+/-} in Pb+Pb reactions were measured at sqrt{s_{NN}}=17.3 GeV by the CERN-NA49 experiment. The nuclear modification factors R_{AA} for pi^{+/-} and R_{CP} for pi^{+/-},p,pbar,K^{+/-} 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. This indicates that the Cronin effect is the dominating effect in our energy range. The modification factor R_{CP}, in which the contribution of the Cron…
We present transverse momentum distributions of charged hadrons produced in Au+Au collisions at $\sqrt{s_{_{NN}}} =$ 200 GeV. The evolution of the spectra for transverse momenta $p_T$ from 0.25 to 5 GeV/C is studied as a function of collision centrality. We find a significant change of the spectral shape between proton-antiproton and peripheral Au+Au collisions. When comparing peripheral to central Au+Au collisions, we find that the yields at the highest $p_T$ exhibit approximate scaling with the number of participating nucleons, rather than scaling with the number of binary collisions.
Two-pion correlations in sqrt(s_NN)=130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k_T by the PHENIX experiment at RHIC. The k_T dependent transverse radii are similar to results from heavy ion collisions at sqrt(s_NN) = 4.1, 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R_out/R_side) is consistent with unity and independent of k_T.
We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt(s_NN) = 200 GeV. The spectra were obtained for transverse momenta 0.25 < p_T < 6.0 GeV/c, in a pseudorapidity range of 0.2 < eta < 1.4 in the deuteron direction. The evolution of the spectra with collision centrality is presented in comparison to p+pbarcollisions at the same collision energy. With increasing centrality, the yield at high transverse momenta increases more rapidly than the overall particle density, leading to a strong modification of the spectral shape. This change in spectr…
In the RHIC run of 2006, PHENIX recorded data from about 20/nb of transversely polarized p+p collisions at sqrt(s) = 62.4 GeV and polarization of about 50%. Also in this last run PHENIX successfully commissioned a new lead-tungstate based electromagnetic calorimeter, the Muon Piston Calorimeter (MPC), covering 2 pi in azimuth and 3.1<eta<3.7. The forward coverage allows PHENIX to measure high x_F pi^0 production. We present the current status of the analysis for the single inclusive pi^0 transverse asymmetry A_N at forward rapidities in PHENIX.
This paper presents the results for the charged-particle multiplicity and transverse energy distributions at mid-rapidity in Au - Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV measured with the PHENIX detector at RHIC. The values of $dN_{ch}/dη_{|η=0}$ and $dE_{T}/dη_{|η=0}$, analyzed as a function of centrality, show a consistent steady rise. For the 5% most central collisions they are $\sim70$% larger compared to the SPS results for Pb-Pb collisions at $\sqrt{s_{_{NN}}}=17.2$ GeV. The ratio of $<E_{T}>/<N_{ch}>$ remains constant as a function of centrality at 0.8 GeV, as also observed at the S…
The STAR collaboration at RHIC reports measurements of the inclusive yield of non-photonic electrons, which arise dominantly from semi-leptonic decays of heavy flavor mesons, over a broad range of transverse momenta ($1.2 < \pt < 10$ \gevc) in \pp, \dAu, and \AuAu collisions at \sqrtsNN = 200 GeV. The non-photonic electron yield exhibits unexpectedly large suppression in central \AuAu collisions at high \pt, suggesting substantial heavy quark energy loss at RHIC. The centrality and \pt dependences of the suppression provide constraints on theoretical models of suppression.
We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at sqrt(s) = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < p_T < 5.0 GeV/c at sqrt(s) = 62.4 GeV and 0.25 < p_T < 7.0 GeV/c at sqrt(s) = 200 GeV, in a pseudo-rapidity range of 0.2 < eta < 1.4. The nuclear modification factor R_AA is calculated relative to p+p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross-section, R_AA is observed to be systematically larger in Cu+Cu collisions compared to Au+Au. Howe…
The almost hermetic coverage of CMS is used to measure the distribution of transverse energy as a function of pseudo-rapidity for pPb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. For minimum bias collisions $(1/N)~dE_T/dη$ reaches 23 GeV which implies an $E_T$ per participant pair comparable to that of peripheral PbPb collisions at $\sqrt{s_{NN}} = 2.76$ TeV. The centrality dependence of transverse energy production has been studied using centrality measures defined in three different angular regions. There is a strong auto-correlation between $(1/N)~dE_T/dη$ and the $η$ range used to define cent…
We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt(s_NN) = 62.4 GeV. The spectra are presented for transverse momenta 0.25 < p_T< 4.5 GeV/c, in a pseudo-rapidity range of 0.2 < eta < 1.4. The nuclear modification factor R_AA is calculated relative to p+p data at the same collision energy as a function of collision centrality. For p_T > 2 GeV/c, R_AA is found to be significantly larger than in Au+Au collisions at sqrt(s_NN) =130 and 200 GeV. In contrast, we find that the evolution of the invariant yields per participant pair from periphera…
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…
We present first measurements of the pseudorapidity and azimuth $(η,ϕ)$ bin-size dependence of event-wise mean transverse momentum $<p_{t} >$ fluctuations for Au-Au collisions at $\sqrt{s_{NN}} = 200$ GeV. We invert that dependence to obtain $p_t$ autocorrelations on differences $(η_Δ,ϕ_Δ)$ interpreted to represent velocity/temperature distributions on ($η,ϕ$). The general form of the autocorrelations suggests that the basic correlation mechanism is parton fragmentation. The autocorrelations vary strongly with collision centrality, which suggests that fragmentation is strongly modified by a di…
The structure of hadron-hadron correlations is investigated in proton-proton collisions.We focus on the transmission of the initial transverse momenta of partons (``intrinsic $k_T$'') to the hadron-hadron correlations. Values of the intrinsic transverse momentum obtained from experimental correlations are compared to the results of a model with partially randomized parton transverse momenta at ISR and RHIC energies. Procedures for extracting the correlations from data are discussed.
We investigate the dependence of elliptic flows $v_2$ on transverse momentum $P_T$ for charged hadrons produced in nucleus-nucleus collisions at high energy by using a multi-source ideal gas model which includes the interaction contribution of the emission sources. Our calculated results are approximately in agreement with the experimental data over a wider $P_T$ range from the STAR and ALICE Collaborations. It is found that the expansion factor increases linearly with the impact parameter from most central (0-5%) to mid-peripheral (35-40%) collisions.
