J/ψ\psi production in In-In and p-A collisions

The NA60 experiment studies dimuon production in In-In and p-A collisions at the CERN SPS. We report recent results on \jpsi production, measured through its muon pair decay. As a function of centrality, we show that in In-In the \jpsi yield is suppressed beyond expectations from nuclear absorption. We present also for the first time results on \jpsi production in p-A collisions at 158 GeV, the same energy of the nucleus-nucleus data. For both p-A and In-In we show preliminary results on \psip suppression. Finally, we have studied the kinematical distributions of the \jpsi produced in In-In collisions. We present results on transverse momentum and rapidity, as well as on the angular distribution of the \jpsi decay products.Comment: 8 pages, Quark Matter 2006 conference proceeding

J/ΨJ/\Psi production in Cu+CuCu+Cu and Au+AuAu+Au collisions measured by PHENIX at RHIC

PHENIX preliminary results on the $J/\Psi$ production in $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV are presented. They are compared to results from lower energy experiments NA50 and NA60 at CERN SPS and to expectations from various theoretical models.Comment: 4 pages, 7 figures, Proceedings for the SQM2006 Conference, submitted to "Journal of Physics G: Nuclear and Particle Physics

NA60 results on pTp_T spectra and the ρ\rho spectral function in In-In collisions

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In-In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of close to 400K events and the good mass resolution of about 2% have made it possible to isolate the excess by subtraction of the decay sources (keeping the $\rho$). The shape of the resulting mass spectrum exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected transverse-momentum spectra have a shape atypical for radial flow and show a significant mass dependence, pointing to different sources in different mass regions.Comment: 4 pages, 4 figures, Quark Matter 2006 conference proceeding

Colour Deconfinement and Quarkonium Binding

At high temperatures, strongly interacting matter becomes a plasma of deconfined quarks and gluons. In statistical QCD, deconfinement and the properties of the resulting quark-gluon plasma can be investigated by studying the in-medium behaviour of heavy quark bound states. In high energy nuclear interactions, quarkonia probe different aspects of the medium formed in the collision. We survey the results of recent charmonium production studies in SPS and RHIC experiments.Comment: 50 pages, 53 figures; revised section 6.

Low Mass Dimuon Production in Indium-Indium Collisions at the CERN SPS

NA60 is a fixed-target experiment at the CERN SPS which measured dimuon production in nucleus-nucleus and proton-nucleus collisions. In this paper we report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions. A significant excess of pairs is observed above the yield expected from neutral meson decays. The excess can be isolated by subtraction of expected sources, thanks to the excellent mass resolution and large sample size.Comment: 4 pages, 3 figures, Contribution at XLIst Rencontres de Moriond, "QCD and High Energy Hadronic Interactions

J/ψ\psi suppression in In-In collisions at 158 GeV/nucleon

The NA60 experiment has studied J/$\psi$ production in Indium-Indium collisions at 158 A$\cdot$GeV. In this paper we present an updated set of results obtained with the complete set of available statistics and an improved alignment of the vertex tracker. The centrality dependence of the J/$\psi$ production, obtained with an analysis technique based only on the J/$\psi$ sample, indicates that a suppression beyond that induced by nuclear absorption is present in In-In collisions, setting in at $\sim$80 participant nucleons. A first study of the systematic errors related with this measurement is discussed. We also present preliminary results on the J/$\psi$ azimuthal distributions.Comment: 8 pages, 3 figures, proceedings of Hard Probes 2006 International Conferenc

A comparative measurement of ϕ→K+K−\phi\rightarrow K^+K^- and ϕ→μ+μ−\phi\rightarrow \mu^+\mu^- in In-In collisions at the CERN SPS

The NA60 experiment at the CERN SPS has studied $\phi$ meson production in In-In collisions at 158A GeV via both the $K^+K^-$ and the $\mu^+\mu^-$ decay channels. The yields and inverse slope parameters of the $m_T$ spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. Possible physics implications are discussed

Evidence for the production of thermal-like muon pairs with masses above 1 GeV/c^2 in 158A GeV Indium-Indium Collisions

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c^2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of {\em prompt} muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c^2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c^2 to be of largely partonic origin, when radial flow has not yet built up.The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c^2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of {\em prompt} muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c^2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c^2 to be of largely partonic origin, when radial flow has not yet built up

First results on angular distributions of thermal dileptons in nuclear collisions

The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters \lambda, \mu and \nu are measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.Comment: Submitted to Physical Review Letter