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Systematics of identified particle spectra

Systematics of identified particle spectra. Levente Molnar, Purdue University For the STAR Collaboration. Outline: Physics motivation Particle spectra and properties at 62.4GeV and beyond … Resonance effect on extracted freeze-out parameters Summary, outlook, …. Motivation.

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Systematics of identified particle spectra

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  1. Systematics of identified particle spectra Levente Molnar, Purdue University For the STAR Collaboration • Outline: • Physics motivation • Particle spectra and properties at 62.4GeV and beyond … • Resonance effect on extracted freeze-out parameters • Summary, outlook, … Levente Molnar, Purdue University

  2. Motivation • New data set: 62.4GeV Au-Au collisions, • first step in the energy scanning program at RHIC. • Bulk particles are the ‘final’ dynamic thermometers of the collision system: • Identified particle spectra at low pT • Study particle production vs. psNN , centrality, … • Particle ratios → chemical freeze-out properties • Shape of the spectra → kinetic freeze-out temperature and transverse radial flow: dynamics of the collision. • Study of resonance decay effect on the extracted freeze-out parameters. Levente Molnar, Purdue University

  3. Identified particle spectra in AuAu at 62.4GeV STAR Preliminary STAR Preliminary STAR Preliminary • Particle spectra are measured at midrapidity: |y| < 0.1 in the STAR-TPC. • Spectra evolution with centrality is similar to that observed at 200GeV. • Particle spectra are fitted with Blast-Wave model (thermal source + flow ) • ( E. Schnedermann et al. PRC48,2462, (1993) ) Levente Molnar, Purdue University

  4. Particle - antiparticle ratios STAR Preliminary STAR Preliminary • Errors shown: • 200GeV systematic errors • 62.4GeV stat. errors BRAHMS, nucl-ex/0410020 • + / -¼ 1. • K- / K+ ratio is smaller at 62.4GeV. • Significant drop in antiproton to proton ratio! • Statistical models are very successful describing ratios from AGS-RHIC. Levente Molnar, Purdue University

  5. Unlike particle ratios vs centrality STAR Preliminary • Errors shown: • 200GeV systematic errors • 62.4GeV stat. errors Levente Molnar, Purdue University

  6. Average transverse momenta STAR Preliminary • <pT> follows the • same trend in Nch • < pT >K,p is extracted • from Blast-Wave fit. • < pT >π is extracted • from Bose-Einstein fit. Nch STAR: 200GeV AuAu: Phys. Rev. Lett. 92 (2004) 11230 • Errors shown: • 200GeV systematic errors • 62.4GeV stat. errors Levente Molnar, Purdue University

  7. Nu Xu, Nucl.Phys. A698 (2002) 306 Tkin and <β> in central heavy ion collisions <β> (c) Tkin (GeV) AGS SPS RHIC AGS SPS RHIC √sNN(GeV) √sNN(GeV) Freeze-out parameters I. STAR Preliminary STAR Preliminary <β> • Errors shown: • 200GeV systematic errors • 62.4GeV stat. errors STAR Preliminary Levente Molnar, Purdue University

  8. Freeze-out parameters II. STAR Preliminary STAR Preliminary Nch  Becattini, hep-ph/0202071 STAR Preliminary • Errors shown: • 200GeV systematic errors • 62.4GeV stat. errors Nch Levente Molnar, Purdue University

  9. The blast wave model study shown so far treated particles as if they were primordial. Systematic errors include resonance effects studied by a stand alone MC. A more complete study of resonance effects based on code from ref.: U.A.Wiedemann, U.Heinz, Phys.Rev. C56 (1997) 3265-3286. Improvements: Increase the number of resonances included: , , ’, , K*, KS, , , , 1520, , 1385, , . Implementation of two freeze-out temperatures Chemical model fit provides Tchem, B, S and . Calculate primordial particle yields Blast wave model; shape of particle spectra including resonances. (Ref.: E. Schnedermann et al. PRC48,2462, (1993) , … ) Resonance decay channels, ref. see above Addition of decay channels ! Inclusive spectra. The inclusive simulated spectra then are fitted to the measured , K, p spectra. Extract Tkin and  for which the 2/ndf is minimum. Estimate of Resonances and Method Levente Molnar, Purdue University

  10. PiMinus Spectra STAR Preliminary Tkin=90MeV b=0.6 n=0.8 • Note: pion spectra (data) are corrected for weak decays, no  and K0Scontributions.. Levente Molnar, Purdue University

  11. KMinus Spectra STAR Preliminary Tkin=90MeV b=0.6 n=0.8 STAR Preliminary Levente Molnar, Purdue University

  12. Proton Spectra STAR Preliminary Tkin=90MeV b=0.6 n=0.8 All Protons Thermal protons Lambda Delta Xi Sigma Omega Sigma1385 Lambda1520 STAR Preliminary • Main contribution from , , , … Levente Molnar, Purdue University

  13. Fit I. STAR Preliminary STAR Preliminary Tkin=90MeV b=0.6 n=0.8 pT (GeV/c) pT (GeV/c) 2/ndf=1.547 • Pion spectra can be reproduced, kaons and protons are less well described . Levente Molnar, Purdue University

  14. Fit II. STAR Preliminary STAR Preliminary 2/ndf=1.396 Tkin=90MeV b=0.64 n=0.8 • Kaons and protons agree well, pions are less well described. • Short lived resonances, eg.:  Levente Molnar, Purdue University

  15. It is an open question what flow velocity and temperature should be assigned to short-lived resonances such as , , … They decay and are regenerated constantly during the system evolution: assume  decay pions and other pions are in equilibrium and behave similarly ( similar temperature and flow velocity ). the  does not gain stronger flow due to its large mass during its short lifetime. Assume  does not contribute to spectral shape change, i.e. we take primordial pion shape for the  decay pions as well.  decays are still included but their contribution is small. Rho contribution Levente Molnar, Purdue University

  16. Fit III. STAR Preliminary STAR Preliminary Tkin=90MeV b=0.64 n=0.8 2/ndf=0.305 • With the  contribution as described before, blast wave describe all spectra well. The parameters agree with published values within syst. errors. Levente Molnar, Purdue University

  17. We have measured π, K, p spectra in 62.4GeV AuAu collisions. • Spectra and particle ratios show similar evolution with centrality as at 200GeV: • K– / π – ratio indicates similar strangeness production. • p / p ratio decreases from 200GeV → 62.4GeV due to the net baryon density, and also decreases with increasing centrality. • Particle production can be described with statistical model over a wide range of collision energies. • The system shows similar freeze-out properties at 62.4GeV as at 200GeV: • Tch is ~ 160MeV ( ~Tc) and independent of centrality. • Tkin decreases and <β> increases from peripheral to central collisions. • Freeze-out parameters seem to follow similar trend in Nch. • Detailed resonance study is performed: • Particle spectra are reproduced in simulation including resonance particles at temperatures and flow velocities within the systematic errors. • Pion spectrum and short lived resonances. • To do: • Further study of resonances, automatic fit to obtain final temperature and flow velocity, 62.4GeV data, … Summary and Outlook Levente Molnar, Purdue University

  18. Levente Molnar, Purdue University

  19. PiMinus Spectra No Rho Levente Molnar, Purdue University

  20. Paper plots • Pion spectra – with the decay channels – as in paper can be reproduced. • Note: linear transverse flow rapidity profile is used in paper: t= f r, where r=0-4. • In the following calculations “regular” flow is used =S (r/R)n=0.8 Levente Molnar, Purdue University

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