Transverse-momentum and collision-energy dependence of high-pT hadron suppression in Au+Au collisions at ultrarelativistic energies

We report high statistics measurements of inclusive charged hadron production in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5相似文献   

Suppressed pi(0) production at large transverse momentum in central Au+Au collisions at sqrt[s(NN)]=200 GeV

Transverse momentum spectra of neutral pions in the range 1相似文献   

J/psi production in sqrt s_NN=200 GeV Cu+Cu collisions

Yields for J/psi production in Cu+Cu collisions at sqrt s_NN=200 GeV have been measured over the rapidity range |y|<2.2 and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data offer greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, in the range where the quark-gluon plasma transition threshold is predicted to lie. Cold nuclear matter estimates based on ad hoc fits to d+Au data describe the Cu+Cu data up to N_part approximately 50, corresponding to a Bjorken energy density of at least 1.5 GeV/fm(3).     

Absence of suppression in particle production at large transverse momentum in sqrt[s(NN)]=200 GeV d+Au collisions

Transverse momentum spectra of charged hadrons with p(T)<8 GeV/c and neutral pions with p(T)<10 GeV/c have been measured at midrapidity by the PHENIX experiment at BNL RHIC in d+Au collisions at sqrt[s(NN)]=200 GeV. The measured yields are compared to those in p+p collisions at the same sqrt[s(NN)] scaled up by the number of underlying nucleon-nucleon collisions in d+Au. The yield ratio does not show the suppression observed in central Au+Au collisions at RHIC. Instead, there is a small enhancement in the yield of high momentum particles.     

Transverse-momentum spectra in Au+Au and d+Au collisions at sqrt[s(NN)]=200 GeV and the pseudorapidity dependence of high-p(T) suppression

We present spectra of charged hadrons from Au+Au and d+Au collisions at sqrt[s(NN)]=200 GeV measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to spectra from p+(-)p collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central Au+Au collisions at eta=0 and eta=2.2 evidence a strong suppression in the high p(T) region (>2 GeV/c). In contrast, the d+Au nuclear modification factor (at eta=0) exhibits an enhancement of the high p(T) yields. These measurements indicate a high energy loss of the high p(T) particles in the medium created in the central Au+Au collisions. The lack of suppression in d+Au collisions makes it unlikely that initial state effects can explain the suppression in the central Au+Au collisions.     

Centrality dependence of charged hadron transverse momentum spectra in Au+Au collisions from sqrt[s(NN)]=62.4 to 200 GeV

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相似文献   

Source breakup dynamics in Au + Au collisions at sqrt[s(NN)]=200 GeV via three-dimensional two-pion source imaging

A three-dimensional correlation function obtained from midrapidity, low p(T), pion pairs in central Au+Au collisions at sqrt[s(NN)]=200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). A proper breakup time tau(0) ~ 9 fm/c and a mean proper emission duration Delta tau ~ 2 fm/c, leading to sizable emission time differences ({|Delta t(LCM)|} approximately 12 fm/c), are required to allow models to be successfully matched to these tails. The model comparisons also suggest an outside-in "burning" of the emission source reminiscent of many hydrodynamical models.     

Transverse momentum and centrality dependence of high-pT nonphotonic electron suppression in Au+Au collisions at sqrt[s NN]=200 GeV

The STAR collaboration at the BNL Relativistic Heavy-Ion Collider (RHIC) reports measurements of the inclusive yield of nonphotonic electrons, which arise dominantly from semileptonic decays of heavy flavor mesons, over a broad range of transverse momenta (1.2相似文献   

Identified baryon and meson distributions at large transverse momenta from Au + Au collisions at square root sNN=200 GeV

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.     

Charged-particle multiplicity near midrapidity in central Au+Au collisions at sqrt[SNN]=56 and 130 GeV

We present the first measurement of pseudorapidity densities of primary charged particles near midrapidity in Au+Au collisions at sqrt[s(NN)] = 56 and 130 GeV. For the most central collisions, we find the charged-particle pseudorapidity density to be dN/deta|(|eta|<1) = 408+/-12(stat)+/-30(syst) at 56 GeV and 555+/-12(stat)+/-35(syst) at 130 GeV, values that are higher than any previously observed in nuclear collisions. Compared to proton-antiproton collisions, our data show an increase in the pseudorapidity density per participant by more than 40% at the higher energy.     

Longitudinal double-spin asymmetry for inclusive jet production in p[over -->] + p[over -->] collisions at sqrt[s]=200 GeV

We report a new STAR measurement of the longitudinal double-spin asymmetry A(LL) for inclusive jet production at midrapidity in polarized p + p collisions at a center-of-mass energy of sqrt[s]=200 GeV. The data, which cover jet transverse momenta 5相似文献   

Centrality dependence of high-p(T) hadron suppression in Au+Au collisions at sqrt[s(NN)]=130 GeV

Inclusive transverse momentum distributions of charged hadrons within 0.2相似文献   

Distributions of charged hadrons associated with high transverse momentum particles in pp and Au+Au collisions at sqrt[sNN]=200 GeV

Charged hadrons in [EQUATION: SEE TEXT] associated with particles of [EQUATION: SEE TEXT] are reconstructed in pp and Au+Au collisions at sqrt[sNN]=200 GeV. The associated multiplicity and p magnitude sum are found to increase from pp to central Au+Au collisions. The associated p distributions, while similar in shape on the nearside, are significantly softened on the awayside in central Au+Au relative to pp and not much harder than that of inclusive hadrons. The results, consistent with jet quenching, suggest that the awayside fragments approach equilibration with the medium traversed.     

Perturbative QCD calculations of elliptic flow and shear viscosity in Au+Au collisions at sqrt[s_{NN}]=200 GeV

The elliptic flow v_{2} and the ratio of the shear viscosity over the entropy density, eta/s, of gluon matter are calculated from the perturbative QCD (pQCD) based parton cascade Boltzmann approach of multiparton scatterings. For Au+Au collisions at sqrt[s]=200A GeV the gluon plasma generates large v_{2} values measured at the BNL Relativistic Heavy Ion Collider. Standard pQCD yields eta/s approximately 0.08-0.15 as small as the lower bound found from the anti-de Sitter/conformal field theory conjecture.     

Onset of pi(0) suppression studied in Cu+Cu collisions at sqrt S NN=22.4, 62.4, and 200 GeV

Neutral pion transverse momentum (p(T)) spectra at midrapidity (|y| less than or approximately 0.35) were measured in Cu+Cu collisions at sqrt[s(NN)]=22.4, 62.4, and 200 GeV. Relative to pi_(0) yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (N(coll) the pi_(0) yields for p(T) more than or approximately 2 GeV/c in central Cu+Cu collisions are suppressed at 62.4 and 200 GeV whereas an enhancement is observed at 22.4 GeV. A comparison with a jet-quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.     

Scaling properties of azimuthal anisotropy in Au+Au and Cu+Cu Collisions at sqrt[s NN]=200 GeV

Differential measurements of elliptic flow (v2) for Au+Au and Cu+Cu collisions at sqrt[sNN]=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v2 with eccentricity, system size, and transverse kinetic energy (KE T). For KE T identical with mT-m up to approximately 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KE T mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v2 for both mesons and baryons over the full KE T range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KE T, rather than transverse momentum.     

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV

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相似文献   

Scaling properties of proton and antiproton production in sqrt[s(NN)]=200 GeV Au+Au collisions

We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt[s(NN)]=200 GeV measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5相似文献   

High-p(T) Tomography of d+Au and Au+Au at SPS,RHIC, and LHC

The interplay of nuclear effects on the p(T)>2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at sqrt[s(NN)]=17, 200, and 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can be used to disentangle the initial and final state effects.