production at sqrt(s)=200GeVSQM 2003

meson production at meson production at GeV from STARGeV from STAR

Jingguo MaUniversity of California, Los Angeles

for the STAR collaboration

I. MotivationsII. Preliminary ResultsIII. Summary

production at sqrt(s)=200GeVSQM 2003

Motivations

Maybe phi can be a good probe of QGP • OZI rule suppression • small cross section for scattering with nonstrange hadrons

•Information from earlier time?•Sensitive to early flow?

Chiral Symmetry Restoration:•mass shift, width broadening?

Production mechanism:•ggg -> •s sbar -> •K+K- ->

• m ~ 1019 MeV/c2

~ 4.45 MeV/c2

• c ~ 41 fm• Vector meson• quark content : s, sbar

• Decay mode: K+ K- (49.2%)

production at sqrt(s)=200GeVSQM 2003

Data set

Number of charged particles

AuAu collisions: MinBias data 2.1M events Central data(top 5%) 0.5M eventspp collisions: 4M events

production at sqrt(s)=200GeVSQM 2003

AuAu collisionsMearsured Mass=1019 MeV/c2, FWHM=7.80.5 MeV/c2

K+K- pair invariant mass

background subtracted

production at sqrt(s)=200GeVSQM 2003

pp collisionsMeasured Mass=1019 MeV/c2, FWHM=7.10.3 MeV/c2

Misidentified KsPhi

K+K- pair invariant mass

background subtracted

production at sqrt(s)=200GeVSQM 2003

Preliminary resultsPreliminary results

Fit functions:AuAu: mt exponentialpp: pt power law

STAR preliminary|y|<0.5;Measured Pt range:0.4GeV~3.9GeV;Exponential function fit well to the spectra of AuAu collisions;Spectra from pp collisions fit well to a power law function; Statistical errors only.

production at sqrt(s)=200GeVSQM 2003

Preliminary resultsPreliminary results

AuAu collisions Spectra in different rapidity bins;Exponential function fit to the spectra; Statistical errors only.

STAR preliminary

production at sqrt(s)=200GeVSQM 2003

dN/dy vs. nCharge

STAR preliminary

• dN/dy increases linearly with nCharge;• Statistical errors only.

production at sqrt(s)=200GeVSQM 2003

Boost invariance

• Boost invariance in |y|<1.0;• Statistical errors only.

STAR preliminary

production at sqrt(s)=200GeVSQM 2003

Phi/K-

STAR preliminary

• N()/K- independent of collision centralities.

production at sqrt(s)=200GeVSQM 2003

Energy dependence

• Data points are from most central heavy ion collisions;• N()/N(h-) increase with beam energy—follow the same trend as the K- production;• Statistical errors only.

STAR preliminary

AGS SPS RHIC

production at sqrt(s)=200GeVSQM 2003

• Data points are from most central heavy ion collisions;• N()/N(K-) independent of beam energy.

Energy dependence

AGS SPS RHIC

STAR preliminary

production at sqrt(s)=200GeVSQM 2003

<p<pTT> centrality dependence> centrality dependence

1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;

Star preliminary

1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;3) -meson seems flow differently.

production at sqrt(s)=200GeVSQM 2003

Lines are from thermal model calculation. Again, <pT> of -meson does not change with centrality.-meson may give earlier partonic information!

<p<pTT> vs. particle mass> vs. particle mass

110MeV,<>=0.55

170MeV,<>=0.0

110MeV,<>=0.0

production at sqrt(s)=200GeVSQM 2003

1) 200 GeV meson production from both AuAu and pp collisions is measured;

2) AuAu spectra fit well to an exponential function, while pp results fit well to a power law function;

3) dN/dy of scales linearly with number of charged particles;

4) dN/dy and inverse slope measurement shows boost invariance for within |y|<1.0;

5) In AuAu collisions, within the measured centrality range, the shape of the transverse momentum distribution weakly depends on the centrality – absence of significant hadronic re-scatterings for phi?

SummarySummary

production at sqrt(s)=200GeVSQM 2003

Phi/nCharge

production at sqrt(s)=200GeVSQM 2003

Measured Mass

0-5% 0-10% 10-30%

30-50% 50-80% pp