Masashi Kaneta, LBNL Masashi Kaneta for the STAR collaboration Lawrence Berkeley National Lab. First results from STAR experiment at RHIC - Soft hadron physics -

Masashi Kaneta, LBNL Focus on Hadrons Measured : h ,  ±, K ±, K 0 s, K *0, K *0, p, p, d, 3 He, 3 He, t,      In future :  0     +      ’,     , J/  and more Freeze-out conditions of low momentum hadrons by Spectra/Ratios Thermal/Chemical Freeze-out Particle correlations Size parameters, Phase space density Event anisotropy v 2

Masashi Kaneta, LBNL Spectra

Masashi Kaneta, LBNL Spectra Momentum distributions Information of thermal (kinetic) freeze-out The inverse slope parameter of m T distribution reflects temperature and radial flow

Masashi Kaneta, LBNL Identified particle spectra p K-K- central collisions  6% 11-18% 26-34% 45-58% 58-85% Only stat. errors are shown

Masashi Kaneta, LBNL Only stat. errors are shown p K-K- central collisions  6% 11-18% 26-34% 45-58% 58-85% Identified particle spectra p K-K- central collisions  6% 11-18% 26-34% 45-58% 58-85% Only stat. errors are shown

Masashi Kaneta, LBNL Thermal(Kinetic) freeze-out Thermal freeze-out at RHIC Temperature is similar at SPS Larger radial flow than at SPS STAR (  s NN =130 GeV) Hydrodynamical model: E. Schnedermann et al. PRC48(1993)2462 m T -mass [GeV/c 2 ] mass [GeV/c 2 ] Inverse slope parameter [GeV/c 2 ]

Masashi Kaneta, LBNL Ratios

Masashi Kaneta, LBNL Ratios p T dependence anti-particle/particle Test slope for particle and anti-particle Anti-baryon/baryon ratio Stopping or transparent? Particle ratios from hadrons Chemical freeze-out parameters

Masashi Kaneta, LBNL p/p ratio Minimum bias data No or weak p T dependence Submitted to PRL Systematic errors<10%

Masashi Kaneta, LBNL / ratio No significant p T dependence in the ratio The mean ratio = 0.72±0.04 From 200 K Central trigger Au+Au Events (top ~15% multiplicity.) Systematic errors are under evaluation |y|<0.5  ratio

Masashi Kaneta, LBNL K + /K  ratio ratio p T [GeV/c] STAR Preliminary |y|<0.5 Event fraction = top 7%

Masashi Kaneta, LBNL Multiplicity dependence of ratios Not baryon free at mid-rapidity An effect of anti-baryon absorption in central collisions? (n ch /n max )  /  Preliminary     Preliminary P e r i p h e r a l  C e n t r a l p/p submitted to PRL p T GeV/c |y|<0.3 Only statistic errors are shown Systematic errors p/p : 10%  and     : under evaluation ratio

Masashi Kaneta, LBNL Chemical freeze-out Baryonic Potential  B [MeV] Chemical Temperature T ch [MeV] AGS SIS LEP/ SppS SPS quarks-gluons hadrons RHIC Experimental ratio Model prediction of ratio 48±12 B

Masashi Kaneta, LBNL HBT

Masashi Kaneta, LBNL HBT Pion HBT Centrality Transverse momentum The HBT excitation function Phase space density Event-by-Event HBT K 0 s K 0 s,  pp, pp  correlations Non-identical particles Many topics in STAR measurement The HBT excitation function Focus in this talk

Masashi Kaneta, LBNL The HBT excitation function Compilation 3D  -HBT parameters as a function of  s ~10% Central Au+Au(Pb+Pb) events y ~ 0 k T  0.17 GeV/c STAR Preliminary No significant jump from SPS to RHIC We need energy scan between both energy

Masashi Kaneta, LBNL Event Anisotropy

Masashi Kaneta, LBNL Event anisotropy In momentum space Anisotropy measured as second harmonic parameter v 2 v 2 will be scale to initial shape parameter , if the source has a hydrodynamical expansion Momentum space Almond shape overlap region in coordinate space

Masashi Kaneta, LBNL Charged particle v 2 versus Multiplicity PRL 86, (2001) 402 |  | < < p T < 2.0 Boxes show “initial spatial anisotropy”  scaled by n ch = primary tracks in |  | < 0.75

Masashi Kaneta, LBNL Charged  and p+p, v 2 (p T ) (M.B.)

Masashi Kaneta, LBNL Comparison with a hydrodynamical model Hydrodynamical calculations: Huovinen, Kolb and Heinz

Masashi Kaneta, LBNL Charged particle anisotropy 0<p T <4.5 GeV/c Minimum bias data Only statistical errors Systematic error 10% - 20% for p t = 2 – 4.5 GeV/c

Masashi Kaneta, LBNL Summary Net-baryon  0 at mid-rapidity Anti-baryon/baryon ratios are toward 1, but still <1 Chemical Freeze-out T ch : same or higher than at SPS  B ： smaller than at SPS HBT parameters Similar to SPS Large anisotropic flow From mid-central to central data, Hydrodynamical model can describe v 2 at low p T (<2GeV/c) Thermal Freeze-out T fo : similar to SPS/AGS Large radial flow We need energy scan between SPS and RHIC!

Masashi Kaneta, LBNL Future plans TOF PID up to 2GeV/c of p T SVT Increasing momentum resolution More strangeness baryons EMC Electron measurement Full fields Higher p T measurement Increasing momentum resolution With high statistics Physics of  0, and resonances

Masashi Kaneta, LBNL  Typical e + e  pair from  e+e+ e+e+ e+e+ e+e+ e-e- e-e- e-e- e-e-  invariant mass [GeV]  STAR Preliminary and 0 The e + e  pair from  conversion is measured Large  acceptance p T = 50 MeV/c to ~4 GeV/c, |  |<1.8