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STAR 2S0Q0M7 Strangeness and bulk freezeout properties at RHIC Aneta Iordanova 24 June 2007 Strangeness in Quark Matter 2007 STAR 2S0Q0M7 Outline Motivation STAR Experiment Analysis Techniques Results Summary Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR Motivation 2S0Q0M7 Identified particle spectra in heavy-ion collisions at different center-of-mass energies and system size provide a unique tool to explore the QCD phase diagram. system size dependence of the freeze-out parameters at RHIC. Bulk properties: - Kinetic freeze-out properties from spectral shapes • Tkin at kinetic freeze-out, transverse radial flow (β) - Chemical freeze-out properties from particle ratios • Tch at chemical freeze-out, strangeness and baryon production Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR 2S0Q0M7 STAR Experiment Time Projection Chamber Measures charged particle momenta and energy loss within |h|<1 Full azimuthal acceptance Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR Analysis Technique 2S0Q0M7 normalized Exploit the ionization energy loss (dE/dx) Distribution is normalized by the theoretical expectation for different particle types; e.g. z(p)=ln[(dE/dx)/(dE/dxTh)]. Cu+Cu 200 GeV 0-10% central Minimum Bias 0.50<pT<0.55 GeV/c z(p) distribution is sliced into dp=50MeV/c for pion kaon electron proton |y|<0.1 (mid-rapidity) 6 centrality bins - corresponding to the top 60% of the cross-section. √sNN=62.4GeV and 200 GeV Consistent analysis technique is used for all low pT measurements for different center-of-mass energies and colliding systems. Raw yields are extracted for different particles from multi-Gaussian fits. Strangeness in Quark Matter 2007 Aneta Iordanova STAR Preliminary 24 June 2007 STAR Results – Particle Spectra 2S0Q0M7 Raw data are corrected for: 10% central, Cu+Cu 200 GeV 62.4 GeV Single particle (track finding) efficiency Energy Loss in the TPC Pions/protons corrected for background p– K– Corrected spectra are shown for mT-m0 p Central 0-10% data Mass dependence is observed in the slope of the spectra shapes Strangeness in Quark Matter 2007 Aneta Iordanova STAR Preliminary 24 June 2007 STAR Results – Particle Ratios 2S0Q0M7 K–/p– ratio Systematically higher in the smaller system p/p– ratio Same for Au+Au and Cu+Cu STAR Preliminary Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 Fitting the data – Statistical Model STAR 2S0Q0M7 The model has 4 fit parameters: chemical freeze-out temperature, Tch baryon chemical potential, μB strangeness chemical potential, μS strangeness suppression, γS g i Si p 2 dp ni (T , ) 2 s ( Ei B Bi S Si ) T 2p e 1 0 STAR Preliminary 10% central, Cu+Cu @ 200 62.4GeV GeV Fit uses only data from p, K and p Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 Chemical freeze-out properties STAR 2S0Q0M7 Strangeness suppression factor consistent within errors with Au+Au results for the central data But appears to be systematically higher for the smaller system Strangeness in Quark Matter 2007 Aneta Iordanova STAR Preliminary 24 June 2007 Chemical freeze-out properties STAR 2S0Q0M7 Chemical freeze-out temperature STAR Preliminary Universal chemical freeze-out temperature, Tch, is observed for all studied systems. Min-Bias Strangeness in Quark Matter 2007 Aneta Iordanova 10% central 5% central 24 June 2007 Chemical freeze-out properties STAR 2S0Q0M7 Chemical freeze-out temperature STAR Preliminary Similar systematic dependence is observed for different ion species as a function of centrality. Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 Fitting the data – Blast –wave model STAR 2S0Q0M7 The model assumes a boosted thermal source in transverse and longitudinal directions. 3 fit parameters are extracted: flow velocity, β kinetic freeze-out temperature, Tkin shape of the flow profile, n r R r r (r ) s (r ) R R n tanh1 r R p sinh mT cosh dn K1 rdrmT I 0 T mT dmT 0 T T kin kin (PR C48 (1993) 2462) Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR 2S0Q0M7 Fit Results Blast wave fits are performed in each centrality bin simultaneously for π±, K±, p and p-bar. For the case of pions, the range below 0.5 GeV/c is excluded in order to reduce effects from resonance contributions. STAR Preliminary 10% central, Cu+Cu @ 200 62.4GeV GeV Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR Particle mean-pT 2S0Q0M7 Particle mean-pT: increases with centrality (Nch). consistent with an increase in radial flow with centrality. Remarkable similarities as a function of Nch are observed. for both Cu+Cu and Au+Au systems at both center-of-mass energies, 200 and 62.4 GeV. Are the bulk properties entropy driven? Strangeness in Quark Matter 2007 Aneta Iordanova * Bose-Einstein fits over the entire fiducial spectra range are used for the case of pions. 24 June 2007 STAR 2S0Q0M7 Kinetic freeze-out properties STAR Preliminary All particle spectra for p±, K±, p and p-bar in Cu+Cu and Au+Au systems appear to be described by a common set of freezeout parameters. Cu+Cu 0-10% Au+Au 0-5% Kinetic Parameters 62.4 GeV 200 GeV 62.4 GeV 200 GeV flow velocity 0.48±0.06 0.52±0.07 0.54±0.01 0.59±0.05 115±7 112±9 93.8±4.1 89±12 Tkin (MeV) Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007 STAR 2S0Q0M7 Kinetic freeze-out properties These extracted freeze-out parameters are found to be similar for an equivalent Nch for both Cu+Cu and Au+Au systems at both center-of-mass energies, 200 and 62.4 GeV. STAR Preliminary Strangeness in Quark Matter 2007 STAR Preliminary Aneta Iordanova 24 June 2007 STAR Summary 2S0Q0M7 STAR has enlarged the variety of hadron spectra measurements at RHIC by providing new results for Cu+Cu at two different center-of-mass energies, √s=200 and 62.4 GeV. Thermal models used for studying kinetic and chemical freezeout properties point to a systematic dependence on the number of charged particles produced Independent of collision system and energy This multi-dimensional systematic study has revealed the importance of the initial collision geometric overlap. Strangeness in Quark Matter 2007 Aneta Iordanova 24 June 2007