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First results from STAR experiment at RHIC - Soft hadron physics -

First results from STAR experiment at RHIC - Soft hadron physics -. Masashi Kaneta for the STAR collaboration Lawrence Berkeley National Lab. Focus on. Hadrons Measured : h - , p ± , K ± , K 0 s , K *0 , K *0 , p , p , d , 3 He , 3 He , t , L , L , X - , X + ,

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First results from STAR experiment at RHIC - Soft hadron physics -

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

  2. Focus on • Hadrons • Measured : h-, p ±, K±, K0s, K*0, K*0, p, p, d, 3He, 3He, t,L, L, X -, X +, • In future :p 0,f,W -+W -,r, w, h, h’, D, L(1520), S(1385), 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 • v2

  3. Spectra

  4. Spectra • Momentum distributions • Information of thermal (kinetic) freeze-out • The inverse slope parameter of mT distribution reflects temperature and radial flow

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

  6. Thermal(Kinetic) freeze-out STAR (sNN=130 GeV) Hydrodynamical model: E. Schnedermann et al. PRC48(1993)2462 mT-mass [GeV/c2] • Thermal freeze-out at RHIC • Temperature is similar at SPS • Larger radial flow than at SPS Inverse slope parameter [GeV/c2] mass [GeV/c2]

  7. Ratios

  8. Ratios • pT 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

  9. p/p ratio • Minimum bias data • No or weak pT dependence Submitted to PRL Systematic errors<10%

  10. L/L ratio • No significant pT dependence in the ratio • The mean ratio = 0.72±0.04 |y|<0.5 L/L ratio • From 200 K Central trigger Au+Au Events (top ~15% multiplicity.) • Systematic errors are under evaluation

  11. K+/K- ratio ratio STAR Preliminary |y|<0.5 Event fraction = top 7% pT [GeV/c]

  12. Multiplicity dependence of ratios • Not baryon free at mid-rapidity • An effect of anti-baryon absorption in central collisions? L/LPreliminary X+/X-Preliminary p/p submitted to PRL pT 0.6-0.8 GeV/c |y|<0.3 Only statistic errors are shown Systematic errors p/p : 10% L/L and X+/X- : under evaluation ratio (nch/nmax) P e r i p h e r a l  C e n t r a l

  13. Chemical freeze-out 48±12 B 250 Model prediction of ratio LEP/ SppS quarks-gluons RHIC 200 SPS 150 AGS Chemical Temperature Tch [MeV] Experimental ratio 100 SIS 50 hadrons 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV]

  14. HBT

  15. HBT Focus in this talk The HBT excitation function Many topics in STAR measurement • Pion HBT • Centrality • Transverse momentum • The HBT excitation function • Phase space density • Event-by-Event HBT • K0s K0s, LL • pp, pp • ppp correlations • Non-identical particles

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

  17. Event Anisotropy

  18. Event anisotropy • In momentum space • Anisotropy measured as second harmonic parameter v2 • v2 will be scale to initial shape parameter e, if the source has a hydrodynamical expansion Momentum space Almond shape overlap region in coordinate space

  19. Charged particle v2 versus Multiplicity • Boxes show “initial spatial anisotropy”e scaled by 0.19-0.25 PRL 86, (2001) 402 || < 1.3 0.1 < pT < 2.0 nch = primary tracks in || < 0.75

  20. Charged p and p+p, v2(pT) (M.B.)

  21. Comparison with a hydrodynamical model • Hydrodynamical calculations: Huovinen, Kolb and Heinz

  22. Charged particle anisotropy 0<pT<4.5 GeV/c • Minimum bias data • Only statistical errors • Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c

  23. Summary • Net-baryon  0 at mid-rapidity • Anti-baryon/baryon ratios are toward 1, but still <1 • Chemical Freeze-out • Tch : 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 v2 at low pT (<2GeV/c) • Thermal Freeze-out • Tfo : similar to SPS/AGS • Large radial flow • We need energy scan between SPS and RHIC!

  24. Future plans • TOF • PID up to 2GeV/c of pT • SVT • Increasing momentum resolution • More strangeness baryons • EMC • Electron measurement • Full fields • Higher pT measurement • Increasing momentum resolution • With high statistics • Physics of g, p0, and resonances

  25. g and p0 STAR Preliminary p0 gg invariant mass [GeV] • The e+e- pair from g conversion is measured • Large g acceptance • pT = 50 MeV/c to ~4 GeV/c, |h|<1.8 Typical e+e-pair from g e+ e+ e- e- e- e+ e- e+

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