We report the first results on differential, total and elastic cross sections in proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) at $\sqrt{s}=200$ GeV. The data lwere obtained with the Roman Pot Detector subsystem of the STAR experiment. The data used for this analysis cover the four-momentum transfer squared ~($t$) range $ 0.045 \le |t| \le 0.135$ (GeV/c)$^2$. The Roman Pot system was placed downstream of the STAR detector. During the data taking the Roman Pots were moved to ~8$σ_{y}$, the vertical distance of from the beam center. They were operated during standard data taking procedure. The results include values of the exponential slope parameter (B), elastic cross section ($σ_{el}$) and the total cross section ($σ_{tot}$) obtained by extrapolation of the elastic differential cross section ($dσ/dt$) to the optical point at $|t| = 0$ (GeV/c)$^{2}$. The detector setup and analysis procedure are reviewed. All results are compared with the world data.
The first result of the pp2pp experiment at RHIC on elastic scattering of polarized protons at sqrt{s} = 200 GeV is reported here. The exponential slope parameter b of the diffractive peak of the elastic cross section in the t range 0.010 <= |t| <= 0.019 (GeV/c)^2 was measured to be b = 16.3 +- 1.6 (stat.) +- 0.9 (syst.) (GeV/c)^{-2} .
We describe a physics program at the Relativistic Heavy Ion Collider (RHIC) with tagged forward protons. The program started with the proton-proton elastic scattering experiment (PP2PP), for which a set of Roman Pot stations was build. The PP2PP experiment took data at RHIC as a dedicated experiment at the beginning of RHIC operations. To expand the physics program to include non-elastic channels with forward protons, like Central Exclusive Production (CEP), Central Production (CP) and Single Diffraction Dissociation (SD), the experiment with its equipment was merged with the STAR experiment a…
The PHENIX experiment at RHIC has measured the ϕ-meson production at mid-rapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at \sqrt{s_{NN}}=200 GeV via the K^+K^- decay mode. The transverse momentum spectra of the ϕ-meson and the nuclear modification factor as a function of centrality are reviewed here.
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, and $p$($\bar{p}$) are studied at mid-rapidity $(\lvert y \rvert < 0.1)$ for different centrality classes. We also present mid-rapidity measurement of particle yields $(dN/dy)$ and particle ratios in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV. The kinetic freeze-out parameters ($T_{kin}$ and $\langle β\rangle$) are extracted from parti…
We report the first measurements of azimuthal anisotropy at midrapidity originated from the dipole asymmetry due to fluctuations in the initial geometry in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. The signal is almost symmetric in pseudorapidity and we report it as a function of pseudorapidity and transverse momentum for different centrality. Results are compared with available model predictions
The 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 on the first measurement of the single spin analyzing power (A_N) at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result, averaged over the whole t-interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A_N. The difference could be explained by an additional contribution of a hadronic spi…
In these proceedings, we present the higher-order cumulants of proton multiplicity distributions of the fixed-target (FXT) run in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 3.0 GeV. The cumulant ratios are presented as a function of centrality and collision energy. The proton cumulant ratio C4/C2 is consistent with fluctuations driven by baryon number conservation and indicates an energy regime dominated by hadronic interactions. These data imply that the QCD critical point could exist at energies higher than 3 GeV if created in heavy-ion collisions.
The first measurement of the $ρ^{0}$ - vector meson elliptic flow $v_{2}$ at mid-rapidity ($|y |$ $<$ 0.5) in $40 - 80$ $%$ centrality in $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR experiment at RHIC is presented. The study is through the $π^{+} π^{-}$ hadronic decay channel of $ρ^{0}$ which has a branching ratio of $\sim$ 100 %. The analysis is being carried out in two different methods. The $v_{2}$ results obtained in these methods are consistent. Number of Constituent Quark (NCQ) scaling of $v_{2}$ of $ρ^{0}$ meson with respect to other hadrons at intermediate $p_{T}$ is …
Feasibility studies of an observation of the exclusive diffractive bremsstrahlung at RHIC at $\sqrt{s} = 200$~GeV and at $\sqrt{s} = 500$~GeV are reported. A simplified approach to the photon and the scattered proton energy reconstruction is used. Influence of possible backgrounds is discussed.
Jets represent an important tool to explore the properties of the hot and dense nuclear matter created in heavy-ion collisions. However, full jet reconstruction in such events is a challenging task due to extremely large and fluctuating background, which generates a large population of combinatorial jets that overwhelm the true hard jet population. In order to carry out accurate, data-driven jet measurements over a broad kinematic range in such conditions of small signal to background, we use several novel approaches in order to measure inclusive charged jet distributions and semi-inclusive ch…
We report the elliptic flow ($v_{2}$) of $K_{s}^{0}$, $Λ$, $\barΛ$, $ϕ$, $Ξ^{-}$, and $\overlineΞ^{+}$ at mid-rapidity for Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The transverse momentum ($p_{T}$) and centrality dependence of $v_{2}$ have been studied. The number of constituent quark (NCQ) scaling for all the (multi-)strange hadrons has also been tested. The dependence in the ratio of average $v_{2}$ ($\langle$$v_{2}$$\rangle$) on centrality shows a deviation from unity indicating a difference in nuclear structure and deformation between the isobars. The results show…
The measurement of the central exclusive production of charged hadron pairs $h^{+}h^{-}$ ($h = π, K, p$) by the STAR experiment at RHIC is reported. The data from proton-proton collisions at $\sqrt{s} = 200$ GeV were used in this study. The pairs of charged hadrons produced in the reaction $pp\to p^\prime+h^{+}h^{-}+p^\prime$ were reconstructed from the tracks in the central detector, while the forward-scattered protons were measured in the Roman Pot system. Differential cross sections were measured in the fiducial region determined by the geometrical acceptance of the experimental setup. They…
We study J/ψproduction in pp collisions at RHIC within the PHENIX detector acceptance range using the color singlet and color octet mechanism which are based on pQCD and NRQCD. Here we show that the color octet mechanism reproduces the RHIC data for J/ψproduction in pp collisions with respect to the p_T distribution, the rapidity distribution and the total cross section at \sqrt s = 200 GeV. The color singlet mechanism leads to a relatively small contribution to the total cross section when compared to the octet contribution.
RHIC is the only spin-polarized proton collider ever built. With a special optics run of $β^\star \approx 22$ m STAR detector system is suitable for an investigation of the spin dependence of elastic proton-proton scattering. This is a brief summary of measurements of spin asymmetries at the center of mass energy $\sqrt{s}=200$ GeV and in the four-momentum transfer squared $-t$ range $0.003 < -t < 0.035$ GeV$^2$ by the STAR experiment at RHIC.
We present the first measurements of the transverse momentum spectra and azimuthal anisotropy of the identified hadrons ($π^{+}$, $π^{-}$, $K^{+}$, $K^{-}$, $p(\bar{p})$, $K^{0}_{s}$, $Λ(\barΛ)$ and $ϕ$) at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5 GeV for various collision centralities. These measurements are compared to corresponding results from other BES energies. The bulk properties of the system, like the chemical and kinetic freeze-out conditions and the collectivity extracted from the measured yields of the produced particles are presented. The difference between baryo…
PHENIX plans for low energy running are presented. Current detector setting makes it possible to measure dielectron spectra down to sqrt(s_NN)=39GeV, and photon/high pT hadron spectra down to below sub-injection energy (sqrt(s_NN)=5-10GeV). The upgrade of the trigger scheme after the installation of VTX detector will enable PHENIX to fully explore the sub-injection energy regime, starting 2011.
The spatial extents of particle emission source in high-energy collisions can be measured using two-particle femtoscopic correlations. In collisions with small multipli cities, such as proton-proton collisions, correlation functions can be distorted by non-femtos copic effects, for example due to the correlations that caused by energy-momentum conservatio n laws, jets and mini-jets. To estimate these effects, a simulation of p+p collisions at $\sqrt{s}$=200 and $\sqrt{s}$=510 GeV using PYTHIA 6.4.28 and HIJING 1.383, and p+Au collisions at $\sqrt{s_{NN}}$=200 GeV using HIJING were performed. C…
Measurements of the longitudinal spin transfer, $D_{LL}$, and the transverse spin transfer, $D_{TT}$, of the $Λ(\barΛ$) hyperon in polarized $p$+$p$ collisions are expected to be sensitive to the helicity distribution and transversity distribution of the $s(\bar{s})$ quark in proton and the corresponding polarized fragmentation functions. This contribution presents the new preliminary results of the $Λ(\barΛ$) $D_{LL}$ and $D_{TT}$ using data collected at RHIC-STAR experiment in 2015, with twice larger statistics than previously published results.
We present the measurement of elliptic flow ($v_{2}$) as a function of transverse momentum ($p_{T}$) for the $ϕ$-meson in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5 and 39 GeV. At low $p_{T}$ $ϕ$-meson $v_{2}$ decreases with decrease in beam energy. The number of constituent quark ($n_{\rm{cq}}$) scaled $v_{2}$ for $ϕ$-meson vs ($m_{T} - m_{0}$)/$n_{\rm{cq}}$ follows similar trend as other hadrons for $\sqrt{s_{NN}}$= 39 GeV whereas the $n_{\rm{cq}}$ scaled $v_{2}$ for $ϕ$-mesons follows a different trend compared to the other hadrons at $\sqrt{s_{NN}}$= 11.5 GeV.
RHIC-PHENIX has observed a large suppression pattern and azimuthal anisotropy of non-photonic electron at mid-rapidity ($\midη\mid<0.35$) in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. To understand these results and the interaction of heavy quarks in the hot and dense medium, experimental determination of production ratio of charm over bottom is one of the most important topics, since the behavior of bottom may differ from charm in the medium. We measured the ratio of charm over bottom and total cross section of bottom via partial reconstruction of D$^0$$\to$e$^+$ K$^-$ $ν_e$ decay in p+p …
We report the measurement of the parity violating single spin asymmetries for inclusive high transverse momentum electrons and positrons in polarized $p+p$ collisions at a center of mass energy of $\sqrt{s}=500$ GeV with the PHENIX detector at RHIC. These electrons are attributed to the decay of $W^\pm$ and $Z^0$ bosons, and measured production cross section is consistent with the expectations. The $W$ production is confirmed for the first time in $p+p$ collisions. Its spin asymmetry in the polarized $p+p$ collisions is a important probe for the quark flavor decomposition of the proton spin.
Measurements of double helicity asymmetries for inclusive hadron production in polarized proton-proton collisions are sensitive to spin-dependent parton distribution functions, in particular to the gluon distribution function. This study focuses on double helicity asymmetries in eta and charged pion production at mid-rapidity, as well as on the eta cross section and fragmentation functions.
In the search of QCD phase boundary and critical point, higher-order cumulants of conserved quantities are proposed as promising observables and have been studied extensively both experimentally and theoretically. In this paper we present cumulant ratios up to $6^{th}$-order of net-proton number distributions in Au+Au collisions at $\sqrt{\mathrm{s_{NN}}}$ = 7.7 - 200 GeV from STAR Beam Energy Scan program phase I and $\sqrt{\mathrm{s}}$ = 200 GeV $p+p$ collisions. The results are compared with various models and Lattice QCD calculations.
The STAR experiment at RHIC measures the longitudinal double-spin asymmetry $A_{LL}$ for a variety of final states in collisions of longitudinally polarized protons to constrain the polarized gluon distribution in the proton. Asymmetries for mid-rapidity charged pion production benefit from large cross-sections and the excellent tracking and particle identification capabilities of the STAR Time Projection Chamber. This contribution presents a measurement of the ratio of cross sections for inclusive $π^{-}$ and $π^{+}$ production using data collected in 2005, as well as a new measurement of $A_…
We report the energy and centrality dependence of dynamical kurtosis for Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV at RHIC. The dynamical kurtosis of net-proton is compared to that of total-proton. The results are also compared with AMPT model calculations.
Results from the PHENIX Collaboration on the production of deuterons and anti-deuterons in collisions between gold nuclei at a nucleon-nucleon center-of-mass energy of sqrt(s) = 200 GeV are presented.
Inclusive transverse momentum spectra of single electrons from Au+Au collisions have been measured at $\sqrt{s_{NN}}$ = 130 GeV and 200 GeV at midrapidity by the PHENIX experiment at RHIC. After subtraction of background from photon conversions and light hadron decays, the spectra appear consistent with semileptonic decays of charmed particles.
We report on the measurement of the central exclusive production process $pp \ \rightarrow \ pXp$ in proton-proton collisions at RHIC with the STAR detector at $\sqrt{\mathrm{s}} = 510$ GeV. At this energy, this process is dominated by a double Pomeron exchange mechanism. The tracks of the centrally produced system $X$ were reconstructed in the central detector of STAR, the Time Projection Chamber and the Time of Flight systems, and were identified using the ionization energy loss and the time of flight method. The diffractively scattered protons, moving intact inside the RHIC beam pipe after …
We compute \frac{dσ}{dp_T} of the J/ψproduction in pp collisions at RHIC at \sqrt s = 500 and 200 GeV by using both the color octet and singlet models in the framework of non-relativistic QCD. The J/ψwe compute here includes the direct J/ψfrom the partonic fusion processes and the J/ψcoming from the radiative decays of χ_J's both in the color octet and singlet channel. The high p_T J/ψproduction cross section is computed within the PHENIX detector acceptance ranges: -0.35 < η< 0.35 and 1.2 < \|η| < 2.4, the central electron and forward muon arms. It is found that the color octet contribution t…
The transverse spin transfer, $D_{TT}$, of $Λ$ and $\overlineΛ$ hyperons in $p$+$p$ collisions is expected to be sensitive to the $s$ and $\bar{s}$ quark transversity distributions in the proton and to the transversely polarized fragmentation functions. The STAR experiment has published the first measurement of the transverse spin transfer of $Λ$ and $\overlineΛ$ hyperons in transversely polarized $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV within pseudo-rapidity $|η| < 1.2$ and for the transverse momenta up to 8 GeV/$c$ based on the data taken in 2012. In 2015, a data sample of $p$+$p$ collisi…
We compare a few types of high energy reactions which seem to be practical for polarimetry at RHIC. Coulomb-nuclear interference (CNI) in pp elastic scattering leads to a nearly energy-independent left-right asymmetry A_N(t) at small t. The systematical uncertainty of this method is evaluated to be ~ 10%. The CNI in proton-nucleus elastic scattering is predicted to result in larger values of A_N(t) and occurs at larger momentum transfer than in pp elastic scattering. This energy independent asymmetry can be used for the polarimetry. As an absolute polarimeter one can use elastic pp scattering …
The Polarized Atomic Hydrogen Gas Jet Target polarimeter is employed by the Relativistic Heavy Ion Collider (RHIC) to measure the absolute polarization of each colliding proton beam. Polarimeter detectors and data acquisition were upgraded in 2015 to increase solid angle, energy range and energy resolution. These upgrades and advanced systematic error analysis along with improved beam intensity and polarization in RHIC runs 2015 ($E_\textrm{beam}=100\,\text{GeV}$) and 2017 ($255\,\text{GeV}$) allowed us to greatly reduce the statistical and systematic uncertainties for elastic spin asymmetries…
In terms of the hadron-string-dynamics (HSD) approach we investigate the correlation function in the azimuthal angle $ψ$ of charged hadrons that is expected to be sensitive to a signal of local strong parity violation. Our analysis of Au+Au collisions is based on the recent STAR data within the RHIC Beam-Energy-Scan (BES) program. The HSD model reasonably reproduces STAR data for $\sqrt{s_{NN}}=$7.7 GeV, while there are some deviations from the experiment at the collision energy of 11.5 GeV and an increase of deviations between theory and experiment at $\sqrt{s_{NN}}=$39 GeV. For reference, th…
We highlight some connections between the final state hadronic observables and the initial conditions using a recently found new exact family of solutions of relativistic hydrodynamics. These relations provide explicit examples of the scaling behaviour in relativistic hydrodynamics and may provide an advanced estimate of the lifetime and the initial energy density in $\sqrt{s_{NN}} = 62.4$, $130$, and $200$ GeV Au+Au collisions at RHIC and $\sqrt{s_{NN}} = 5.0$ TeV Pb+Pb and $5.44$ TeV Xe+Xe as well as $\sqrt{s} = 7$, $8$ and $13$ TeV p+p collisions at LHC energies. A surprising result is that…
High yield of strange particle production per central collision in nucleus-nucleus collisions at RHIC and high statistics data set from STAR experiment allow us to measure ΛΛcorrelations. The ΛΛcorrelation measurement is also closely related to a possible six-quark state H-dibaryon, which is yet to be observed experimentally. The first measurement of ΛΛcorrelations in Au+Au collisions for \sqrt{s_{NN}}= 39, 62.4 and 200 GeV and search for H-dibaryon with its weak decay Λpπin Au+Au collisions for \sqrt{s_{NN}}= 200 GeV using the STAR experiment at RHIC are presented here.
Jet production in polarized $p+p$ collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500$ GeV provides a powerful probe to study gluons inside the proton. The Solenoidal Tracker at RHIC (STAR) has the capability, with nearly full azimuthal ($2π$) coverage, to reconstruct jets at mid-rapidity ($|η| < 1$). The latest STAR inclusive jet longitudinal double-spin asymmetry $A_{LL}$ measured in 200 GeV $p+p$ collisions provides better constraints on the polarized gluon distribution $Δg(x)$ for $0.05<x<0.2$ than previous measurements. A recent global QCD fit (DSSV 2014) which includes the 2009 RHIC r…
One of the main objectives of the high-energy spin physics program at RHIC at BNL is the precise determination of the polarized gluon distribution function, $Δg(x)$. Polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200\,$GeV and at $\sqrt{s}=500\,$GeV at RHIC provide an unique way to probe the proton spin structure. Inclusive measurements, such as inclusive jet and hadron production, have so far been the prime focus of various results at $\sqrt{s}=200\,$GeV constraining $Δg(x)$ for $0.05<x<0.2$. A recent global analysis provides for the first time evidence of a non-zero value of the gluon p…
Experimental results of the rapidity spectra of protons and net-protons (protons minus antiprotons) emitted in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions, measured by a few collaborations at the alternating gradient synchrotron (AGS), super proton synchrotron (SPS), and relativistic heavy ion collider (RHIC), are described by a three-source distribution. The values of the distribution width $σ_C$ and contribution ratio (relative contribution) $k_C$ of the central rapidity region, and the distribution width $σ_F$ and rapidity shift $Δy$ of the forward/backward rapidity regions, are then…
The RHIC spin program will probe the spin structure of the proton with polarized quarks and gluons by colliding beams of polarized protons at Brookhaven. The first collisions, at sqrt(s)=200GeV, were recorded this year in December 2001 and January 2002. This report describes the first run, and our plans for the next five+ years, with planned runs at sqrt(s)=200 and 500GeV, and luminosity L=2x10^{32} cm^{-2}s^{-1}. See also the presentation at Moriond by Bernd Surrow on the first run with the STAR detector. Here we include a first look at measurements with the PHENIX and PP2PP detectors.
A major goal of the RHIC spin program is to measure Δg, the gluon contribution to the proton's spin. Measurements by PHENIX of the double longitudinal spin asymmetry, A_LL, of the neutral pion production at mid-rapidity in polarized proton collisions have been shown to constrain Δg. Results from the 2005 RHIC run, as well as high p_T data from the 2006 RHIC run, are presented. The results disfavor maximal positive and negative values of Δg. A measurement of azimuthally independent double transverse spin asymmetry, A_TT, is also presented.
The PP2PP experiment is devoted to the proton-proton elastic scattering measurement at the Relativistic Heavy Ion Collider at the centre-of-mass energies between 50 and 500 GeV and the four-momentum transfer $0.0004 \leq |t| \leq 1.3$ Gev$^2$. The option of polarized proton beams offers a unique possibility to investigate the spin dependence of the proton elastic scattering in a systematic way. The energy dependence of the total and elastic cross section, the ratio of the real to the imaginary part of the forward scattering amplitude, and the nuclear slope parameter will be studied. In the med…
A $ρ(770)^0$ mass shift of about -40 MeV/$c^2$ was measured in $p+p$ collisions at $\sqrt{s_{_{NN}}} = $ 200 GeV at RHIC. Previous mass shifts have been observed at CERN-LEBC-EHS and CERN-LEP. We will show that phase space does not account for the $ρ(770)^0$ mass shift measured at RHIC, CERN-LEBC-EHS and CERN-LEP and conclude that there are significant scattering interactions in $p+p$ collisions.
High pT hadrons produced in ultra-relativistic heavy-ion collisions at RHIC probe nuclear matter at extreme conditions of high energy density. Experimental measurements in Au+Au collisions at \sqrtsNN=130, 200 GeV establish the existence of strong medium effects on hadron production well into the perturbative regime.
We present results and predictions for the nuclear modification of the differential cross sections for inclusive light hadron and prompt photon production in minimum bias d+Au collisions at $\sqrt{s} = 200$ GeV and minimum bias p+Pb collisions at $\sqrt{s} = 5$ TeV at RHIC and LHC, respectively. Our calculations combine the leading order perturbative QCD formalism with cold nuclear matter effects that arise from the elastic, inelastic and coherent multiple scattering of partons in large nuclei. We find that a theoretical approach that includes the isospin effect, Cronin effect, cold nuclear ma…
The Relativistic Heavy-Ion Collider (RHIC) provides Au+Au collisions at energies up to \sqrtsNN=200 GeV. STAR experiment was designed and constructed to investigate the behavior of strongly interacting matter at high energy density. An overview of some of the recent results from the STAR collaboration is given.
The charm production is sensitive to early dynamics of the created system in RHIC heavy ion collisions. Dominant process of charm quarks production at RHIC is believed to be initial gluon fusion which can be calculated in the perturbative QCD. Understanding both the charm production total cross section and the fragmentation in p+p collisions is a baseline to further exploring the QCD medium via open charm and charmonium in heavy ion collisions. In this paper we present the first reconstruction of open charm meson $D^{0}$ via the weak decay to K and $π$ mesons in the p+p collisions at $\sqrt{s}…
The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is providing fundamental measurements in high-energy polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200-500\,$GeV to deepen our understanding on the spin structure and dynamics of the proton. This program has completed the first data taking period in 2009 of polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=500\,$GeV. This opens a new era in the study of the spin-flavor structure of the proton based on the production of $W^{-(+)}$ bosons. The measurement of the cross section and single-spin asym…
We analyze the transverse momentum spectra of charged pions measured in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV using the Tsallis distribution modified to include transverse flow. All the spectra are well described by the modified Tsallis distribution in an extended transverse momentum range upto 6 GeV/$c$. The kinetic freeze-out temperature ($T$), average transverse flow ($β$) and degree of non thermalization ($q$) are obtained as a function of system size for both the energies. With increasing system size $β$ shows increasing trend …
