The PHENIX experiment has measured mid-rapidity transverse momentum spectra (0.4 < p_T < 4.0 GeV/c) of single electrons as a function of centrality in Au+Au collisions at sqrt(s_NN) = 200 GeV. Contributions to the raw spectra from photon conversions and Dalitz decays of light neutral mesons are measured by introducing a thin (1.7% X_0) converter into the PHENIX acceptance and are statistically removed. The subtracted ``non-photonic'' electron spectra are primarily due to the semi-leptonic decays of hadrons containing heavy quarks (charm and bottom). For all centralities, charm production is found to scale with the nuclear overlap function, T_AA. For minimum-bias collisions the charm cross section per binary collision is N_cc^bar/T_AA = 622 +/- 57 (stat.) +/- 160 (sys.) microbarns.
The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.
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 hydrodynamic is found to describe the bulk transport of the pions in the longitudinal direction.
Momentum spectra of charged pions over nearly full rapidity coverage from target to beam rapidity have been measured in the 0-5% most central Au+Au collisions in the beam energy range from 2 to 8 AGeV by the E895 Experiment. Using a thermal parameterization to fit the transverse mass spectra, rapidity density distributions are extracted. The observed spectra are compared with predictions from the RQMD v2.3 cascade model and also to a thermal model including longitudinal flow. The total 4$\pi$ yields of the charged pions are used to infer an initial state entropy produced in the collisions.
Phi meson production is studied by the NA49 collaboration in central Pb+Pb collisions at 20A, 30A, 40A, 80A and 158A GeV beam energy. The data are compared to measurements at lower and higher energies and to microscopic and thermal models. The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.
Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed.
New results on the production of charged pions in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. Pions are identified by energy loss measurement in a large TPC tracking system which covers a major fraction of the production phase space. Inclusive invariant cross sections are given on a grid of nearly 300 bins per charge over intervals from 0 to 2 GeV/c in transverse momentum and from 0 to 0.85 in Feynman x. The results are compared to existing data in overlapping energy ranges.
We report measurements of the inclusive J/$\psi$ yield and average transverse momentum as a function of charged-particle pseudorapidity density ${\rm d}N_{\rm ch}/{\rm d}\eta$ in p-Pb collisions at $\sqrt{s_{\rm NN}}= 5.02$ TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/$\psi$ yield with normalised ${\rm d}N_{\rm ch}/{\rm d}\eta$, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/$\psi$ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity.
The ALICE collaboration reports the measurement of the inclusive J/psi yield as a function of charged particle pseudorapidity density dN_{ch}/deta in pp collisions at sqrt{s} = 7 TeV at the LHC. J/psi particles are detected for p_t > 0, in the rapidity interval |y| < 0.9 via decay into e+e-, and in the interval 2.5 < y < 4.0 via decay into mu+mu- pairs. An approximately linear increase of the J/psi yields normalized to their event average (dN_{J/psi}/dy)/<dN_{J/psi}/dy> with (dN_{ch}/deta)/<dN_{ch}/deta> is observed in both rapidity ranges, where dN_{ch}/deta is measured within |eta| < 1 and p_t > 0. In the highest multiplicity interval with <dN_{ch}/deta(bin)> = 24.1, corresponding to four times the minimum bias multiplicity density, an enhancement relative to the minimum bias J/psi yield by a factor of about 5 at 2.5 < y < 4 (8 at |y| < 0.9) is observed.
Invariant pT spectra and rapidity densities covering a large rapidity range(-0.1 < y < 3.5) are presented for $\pi^{\pm}$ 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 ($\pi^-/\pi^+ \sim 1$, $K^-/K^+ \sim 0.85$) while the anti-proton to proton ratio is $\bar{p}/p \sim 0.49$. The rapidity dependence of the $\pi^-/\pi^+$ ratio is consistent with a small increase towards forward rapidities while the $K^-/K^+$ and $\bar{p}/p$ ratios show a steep decrease to $\sim$ 0.3 for kaons and 0.022 for protons at $y\sim 3$. It is observed that the kaon production relative to its own anti-particle as well as to pion production in wide rapidity and energy ranges shows an apparent universal behavior consistent with the baryo-chemical potential, as deduced from the $\bar{p}/p$ ratio, being the driving parameter.
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