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Systematics of identified particle spectra

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Particle spectra and properties at 62.4GeV and beyond ... from Bose-Einstein fit. Errors shown: 200GeV systematic errors. 62.4GeV stat. errors ... – PowerPoint PPT presentation

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Title: Systematics of identified particle spectra


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,

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.

3
Identified particle spectra in AuAu at 62.4GeV
STAR Preliminary
STAR Preliminary
STAR Preliminary
  • Particle spectra are measured at midrapidity
    y lt 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) )

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.

5
Unlike particle ratios vs centrality
STAR Preliminary
  • Errors shown
  • 200GeV systematic errors
  • 62.4GeV stat. errors

6
Average transverse momenta
STAR Preliminary
  • ltpTgt follows the
  • same trend in Nch
  • lt pT gtK,p is extracted
  • from Blast-Wave fit.
  • lt pT gtp 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

7
Freeze-out parameters I.
STAR Preliminary
STAR Preliminary
ltßgt
  • Errors shown
  • 200GeV systematic errors
  • 62.4GeV stat. errors

STAR Preliminary
8
Freeze-out parameters II.
STAR Preliminary
STAR Preliminary
Nch
?
Becattini, hep-ph/0202071
  • Errors shown
  • 200GeV systematic errors
  • 62.4GeV stat. errors

STAR Preliminary
Nch
9
Estimate of Resonances and Method
  • 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.

10
PiMinus Spectra
STAR Preliminary
Tkin90MeV b0.6 n0.8
  • Note pion spectra (data) are corrected for weak
    decays, no ? and K0Scontributions..

11
KMinus Spectra
STAR Preliminary
Tkin90MeV b0.6 n0.8
STAR Preliminary
12
Proton Spectra
STAR Preliminary
Tkin90MeV b0.6 n0.8
All Protons Thermal protons Lambda Delta Xi Sigma
Omega Sigma1385 Lambda1520
STAR Preliminary
  • Main contribution from ?, ?, ?,

13
Fit I.
STAR Preliminary
STAR Preliminary
Tkin90MeV b0.6 n0.8
pT (GeV/c)
pT (GeV/c)
?2/ndf1.547
  • Pion spectra can be reproduced, kaons and
    protons are less well described .

14
Fit II.
STAR Preliminary
STAR Preliminary
?2/ndf1.396
Tkin90MeV b0.64 n0.8
  • Kaons and protons agree well, pions are less
    well described.
  • Short lived resonances, eg. ?

15
Rho contribution
  • 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.

16
Fit III.
STAR Preliminary
STAR Preliminary
Tkin90MeV b0.64 n0.8
?2/ndf0.305
  • With the ? contribution as described before,
    blast wave describe all spectra well. The
    parameters agree with published values within
    syst. errors.

17
Summary and Outlook
18
(No Transcript)
19
PiMinus Spectra No Rho
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 r0-4.
  • In the following calculations regular flow is
    used ??S (r/R)n0.8
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