Publications (109)186.79 Total impact
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Article: Multiplicity distributions and charged-neutral fluctuations
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ABSTRACT: Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as N part 1.07±0.05 and photos as N part 1.12±0.03 have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.Pramana 04/2012; 57(2):285-300. · 0.57 Impact Factor -
Article: Suppression of high-p{T} neutral pion production in central Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV relative to p+C and p+Pb collisions.
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ABSTRACT: Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at sqrt[S{NN}]=17.4 GeV at midrapidity (2.3 less than or approximately equal eta{lab} less than or approximately equal 3.0) over the range 0.7 less than or approximately equal p{T} less than or approximately equal 3.5 GeV/c. The spectra are compared to pi{0} spectra measured in Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N{part} less than or approximately equal 300), the yield of pi{0}'s with p{T} greater than or approximately equal 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N{coll}), while for central Pb+Pb collisions with N{part}greater than or approximately equal 350, the pi{0} yield is suppressed.Physical Review Letters 06/2008; 100(24):242301. · 7.37 Impact Factor -
Article: Rapidity and species dependence of particle production at large transverse momentum for d+Au collisions at √sNN=200 GeV
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ABSTRACT: We determine rapidity asymmetry in the production of charged pions, protons, and antiprotons for large transverse momentum (pT) for d+Au collisions at √sNN=200 GeV. The rapidity asymmetry is defined as the ratio of particle yields at backward rapidity (Au beam direction) to those at forward rapidity (d beam direction). 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+antiproton production in both the 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 multiple scattering, energy loss, nuclear shadowing, saturation effects, and recombination and also to a phenomenological parton model. We find that asymmetries are sensitive to model parameters and show model preference. The rapidity dependence of π-/π+ and p̅ /p ratios in peripheral d+Au and forward neutron-tagged events are used to study the contributions of valence quarks and gluons to particle production at high pT.Phys. Rev. C. 11/2007; 76(5). -
Article: Two-particle correlations on transverse momentum and momentum dissipation in Au–Au collisions at = 130 GeV
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ABSTRACT: Measurements of two-particle correlations on transverse momentum pt for Au–Au collisions at GeV are presented. Significant large-momentum-scale correlations are observed for charged primary hadrons with 0.15 ≤ pt ≤ 2 GeV/c and pseudorapidity |η| ≤ 1.3. Such correlations were not observed in a similar study at lower energy and are not predicted by theoretical collision models. Their direct relation to mean-pt fluctuations measured in the same angular acceptance is demonstrated. Positive correlations are observed for pairs of particles which have large pt values while negative correlations occur for pairs in which one particle has large pt and the other has much lower pt. The correlation amplitudes per final state particle increase with collision centrality. The observed correlations are consistent with a scenario in which the transverse momentum of hadrons associated with initial-stage semi-hard parton scattering is dissipated by the medium to lower pt.Journal of Physics G Nuclear and Particle Physics 03/2007; 34(5):799. · 4.18 Impact Factor -
Article: ΔϕΔη correlations in central Au+Au collisions at √sNN=200 GeV
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ABSTRACT: We report charged particle pair correlation analyses in the space of Δϕ (azimuth) and Δη (pseudorapidity), for central Au+Au collisions at √sNN=200 GeV in the STAR detector. The analysis involves unlike-sign charged pairs and like-sign charged pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We present detailed parametrizations of the data. A model featuring dense gluonic hot spots as first proposed by Van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur, and the model also motivates selection of transverse momenta in the range 0.8<pt<2.0 GeV/c. Both CD and CI correlations of high statistical significance are observed, and possible interpretations are discussed.Phys. Rev. C. 03/2007; 75(3). -
Article: Scaling properties of hyperon production in Au+Au collisions at square root [sNN]=200 GeV.
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ABSTRACT: We present the scaling properties of Lambda, Xi, and Omega in midrapidity Au+Au collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider at sqrt[s_{NN}]=200 GeV. The yield of multistrange baryons per participant nucleon increases from peripheral to central collisions more rapidly than that of Lambda, indicating an increase of the strange-quark density of the matter produced. The strange phase-space occupancy factor gamma_{s} approaches unity for the most central collisions. Moreover, the nuclear modification factors of p, Lambda, and Xi are consistent with each other for 2<p_{T}<5 GeV/c in agreement with a scenario of hadron formation from constituent quark degrees of freedom.Physical Review Letters 02/2007; 98(6):062301. · 7.37 Impact Factor -
Article: The energy dependence of pt angular correlations inferred from mean-pt fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
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ABSTRACT: We present the first study of the energy dependence of pt angular correlations inferred from event-wise mean transverse momentum pt fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies , 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. pt angular correlation structure suggests that the principal source of pt correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with from the onset of observable jet-related pt fluctuations near 10 GeV.Journal of Physics G Nuclear and Particle Physics 01/2007; 34(3):451. · 4.18 Impact Factor -
Article: Proton-Λ correlations in central Au+Au collisions at √sNN=200 GeV
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ABSTRACT: We report on p-Λ,p-Λ̅ ,p̅ -Λ, and p̅ -Λ̅ correlation functions constructed in central Au-Au collisions at √sNN=200 GeV by the STAR experiment at RHIC. The proton and lambda source size is inferred from the p-Λ and p̅ -Λ̅ correlation functions. It is found to be smaller than the pion source size also measured by the STAR experiment at smaller transverse masses, in agreement with a scenario of a strong universal collective flow. The p-Λ̅ and p̅ -Λ correlation functions, which are measured for the first time, exhibit a large anticorrelation. Annihilation channels and/or a negative real part of the spin-averaged scattering length must be included in the final-state interactions calculation to reproduce the measured correlation function.Phys. Rev. C. 12/2006; 74(6). -
Article: Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at square root of s = 200 GeV.
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ABSTRACT: We report a measurement of the longitudinal double-spin asymmetry A(LL) and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at square root of s = 200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A(LL) data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.Physical Review Letters 12/2006; 97(25):252001. · 7.37 Impact Factor -
Article: Neutral kaon interferometry in Au+Au collisions at √sNN=200 GeV
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ABSTRACT: We present the first statistically meaningful results from two-Ks0 interferometry in heavy-ion collisions at √sNN=200 GeV. A model that takes the effect of the strong interaction into account has been used to fit the measured correlation function. The effects of single and coupled channels were explored. At the mean transverse mass 〈mT〉=1.07 GeV, we obtain the values R=4.09±0.46(stat)±0.31(sys) fm and λ=0.92±0.23(stat)±0.13(sys), where R and λ are the invariant radius and chaoticity parameters, respectively. The results are qualitatively consistent with mT systematics established with pions in a scenario characterized by a strong collective flow.Phys. Rev. C. 11/2006; 74(5). -
Article: Direct observation of dijets in central Au+Au collisions at sqrt[sNN]=200 GeV.
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ABSTRACT: The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum (pT) charged hadrons in Au+Au collisions at higher pT than reported previously. As (pT) is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter.Physical Review Letters 11/2006; 97(16):162301. · 7.37 Impact Factor -
Article: Forward neutral pion production in p + p and d + Au collisions at square root sNN=200 GeV.
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ABSTRACT: Measurements of the production of forward pi0 mesons from p + p and d + Au collisions at square root sNN=200 GeV are reported. The p + p yield generally agrees with next-to-leading order perturbative QCD calculations. The d + Au yield per binary collision is suppressed as eta increases, decreasing to approximately 30% of the p + p yield at eta =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward pi0 with charged hadrons at eta approximately 0 show a recoil peak in p + p that is suppressed in d + Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei.Physical Review Letters 11/2006; 97(15):152302. · 7.37 Impact Factor -
Article: Pion freeze-out time in Pb+Pb collisions at 158 AGeV/c studied via π-/π+ and K-/K+ ratios
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ABSTRACT: The effect of the final state Coulomb interaction on particles produced in Pb+Pb collisions at 158 AGeV/c has been investigated in the WA98 experiment through the study of the π-/π+ and K-/K+ ratios measured as a function of mT-m0. While the ratio for kaons shows no significant mT dependence, the π-/π+ ratio is enhanced at small mT-m0 values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the π-/π+ ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.European Physical Journal C 10/2006; 48(2):343-352. · 3.63 Impact Factor -
Article: Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV.
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ABSTRACT: Transverse momentum spectra of pi+/-, p, and p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at square root sNN=200 GeV are presented. In central Au + Au collisions, both pi +/- and p(p) show significant suppression with respect to binary scaling at pT approximately >4 GeV/c. Protons and antiprotons are less suppressed than pi+/-, in the range 1.5 approximately < pT approximately < 6 GeV/c. The pi-/pi+ and p/p ratios show at most a weak pT dependence and no significant centrality dependence. The p/pi ratios in central Au + Au collisions approach the values in p + p and d + Au collisions at pT approximately >5 GeV/c. The results at high pT indicate that the partonic sources of pi+/-, p, and p have similar energy loss when traversing the nuclear medium.Physical Review Letters 10/2006; 97(15):152301. · 7.37 Impact Factor -
Article: Strange baryon resonance production in sqrt s NN=200 GeV p+p and Au+Au collisions.
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ABSTRACT: We report the measurements of Sigma(1385) and Lambda(1520) production in p+p and Au+Au collisions at sqrt[s{NN}]=200 GeV from the STAR Collaboration. The yields and the p(T) spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central Au+Au collisions. Our results indicate that there may be a time span between chemical and thermal freeze-out during which elastic hadronic interactions occur.Physical Review Letters 10/2006; 97(13):132301. · 7.37 Impact Factor -
Article: Minijet deformation and charge-independent angular correlations on momentum subspace (η,ϕ) in Au-Au collisions at √sNN=130 GeV
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ABSTRACT: Measurements of two-particle correlations on angular difference variables η1-η2 (pseudorapidity) and ϕ1-ϕ2 (azimuth) are presented for all primary charged hadrons with transverse momentum 0.15≤pt≤2 GeV/c and |η|≤1.3 from Au-Au collisions at √sNN=130 GeV. Large-amplitude correlations are observed over a broad range in relative angles where distinct structures appear on the same-side and away-side (i.e., relative azimuth less than π/2 or greater than π/2). The principal correlation structures include that associated with elliptic flow plus a strong, same-side peak. It is hypothesized that the latter results from correlated hadrons associated with semi-hard parton scattering in the early stage of the heavy-ion collision which produces a jet-like correlation peak at small relative angles. The width of the jet-like peak on η1-η2 increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. The new methods of jet analysis introduced here provide access to scattered partons at low transverse momentum well below the kinematic range where perturbative quantum chromodynamics and standard fragmentation models are applicable.Phys. Rev. C. 06/2006; 73(6). -
Article: Transverse-momentum pt correlations on (η, ) from mean-pt fluctuations in Au–Au collisions at GeV
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ABSTRACT: We present first measurements of the pseudorapidity and azimuth (η, ) bin-size dependence of event-wise mean transverse-momentum pt fluctuations for Au–Au collisions at GeV. We invert that dependence to obtain pt autocorrelations on differences (ηΔ, Δ) interpreted to represent velocity/temperature distributions on (η, ). The general form of the autocorrelations suggests that the basic correlation mechanism is parton fragmentation. The autocorrelations vary rapidly with collision centrality, which suggests that fragmentation is strongly modified by a dissipative medium in the more central Au–Au collisions relative to peripheral or p–p collisions.Journal of Physics G Nuclear and Particle Physics 05/2006; 32(6):L37. · 4.18 Impact Factor -
Article: Multiplicity and pseudorapidity distributions of charged particles and photons at forward pseudorapidity in Au+Au collisons at √sNN=62.4 GeV
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ABSTRACT: We present the centrality-dependent measurement of multiplicity and pseudorapidity distributions of charged particles and photons in Au+Au collisions at √sNN=62.4 GeV. The charged particles and photons are measured in the pseudorapidity region 2.9≤η≤3.9 and 2.3≤η≤3.7, respectively. We have studied the scaling of particle production with the number of participating nucleons and the number of binary collisions. The photon and charged particle production in the measured pseudorapidity range has been shown to be consistent with energy-independent limiting fragmentation behavior. Photons are observed to follow a centrality-independent limiting fragmentation behavior, while for charged particles it is centrality dependent. We have carried out a comparative study of the pseudorapidity distributions of positively charged hadrons, negatively charged hadrons, photons, pions, and net protons in nucleus-nucleus collisions and pseudorapidity distributions from p+p collisions. From these comparisons, we conclude that baryons in the inclusive charged particle distribution are responsible for the observed centrality dependence of limiting fragmentation. The mesons are found to follow an energy-independent behavior of limiting fragmentation, whereas the behavior of baryons is energy dependent.Phys. Rev. C. 03/2006; 73(3). -
Article: Directed flow in Au+Au collisions at √sNN=62.4 GeV
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ABSTRACT: We present the directed flow (v1) measured in Au+Au collisions at √sNN=62.4 GeV in the midpseudorapidity region |η|<1.3 and in the forward pseudorapidity region 2.5<|η|<4.0. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider, the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons.Phys. Rev. C. 03/2006; 73(3). -
Article: Event-by-event study of DCC-like fluctuation in ultra-relativistic nuclear collisions
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ABSTRACT: A method based on sliding window scheme is developed to search for patches in the pseudorapidity-azimuth plane, on an event-by-event basis, having unusual fluctuation in the neutral pion fraction which may arise due to the formation of Disoriented Chrial Condensates (DCC) in high energy nuclear collisions. The efficiency of the method to extract the patches and the purity of the extracted sample are studied for possible experimental situations. Comment: 10 pages, 5 figures02/2006;
Top co-authors
Top Journals
Institutions
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2003–2012
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Panjab University
Chandīgarh, Union Territory of Chandigarh, India
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2007
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Michigan State University
East Lansing, MI, USA
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2006–2007
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Valparaiso University (USA)
Valparaiso, IN, USA -
Yale University
New Haven, CT, USA -
Variable Energy Cyclotron Centre
Calcutta, Bengal, India
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2003–2007
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University of Birmingham
Birmingham, ENG, United Kingdom
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2005
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Argonne National Laboratory
Downers Grove, IL, USA
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2002
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Central University of Punjab
Batāla, State of Punjab, India
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