f meson production at 200 GeV from STAR Jingguo Ma University of California, Los Angeles for the STAR collaboration I. Motivations II. Preliminary Results III. Summary
Motivations • m ~ 1019 MeV/c2 • ~ 4.45 MeV/c2 • ct ~ 41 fm • Vector meson • quark content : s, sbar • Decay mode: • K+ K- (49.2%) • 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- ->
Data set Number of charged particles AuAu collisions: MinBias data 2.1M events Central data(top 5%) 0.5M events pp collisions: 4M events
K+K- pair invariant mass background subtracted AuAu collisions Mearsured Mass=1019 MeV/c2,FWHM=7.80.5 MeV/c2
K+K- pair invariant mass Misidentified Ks Phi background subtracted pp collisions Measured Mass=1019 MeV/c2, FWHM=7.10.3 MeV/c2
Preliminary results • |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. STAR preliminary Fit functions: AuAu: mt exponential pp: pt power law
Preliminary results STAR preliminary • AuAu collisions Spectra in different rapidity bins; • Exponential function fit to the spectra; • Statistical errors only.
dN/dy vs. nCharge STAR preliminary • dN/dy increases • linearly with nCharge; • • Statistical errors only.
Boost invariance STAR preliminary • Boost invariance in |y|<1.0; • • Statistical errors only.
Phi/K- STAR preliminary • N()/K- independent of collision centralities.
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
Energy dependence STAR preliminary • Data points are from most central heavy ion collisions; • N()/N(K-) independent of beam energy. AGS SPS RHIC
<pT> centrality dependence 1)p, 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; 1)p, 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)f-meson seems flow differently. Star preliminary
<pT> vs. particle mass 110MeV,<>=0.55 170MeV,<>=0.0 110MeV,<>=0.0 Lines are from thermal model calculation. Again, <pT> of f-meson does not change with centrality. f-meson may give earlier partonic information!
Summary • 200 GeV f meson production from both AuAu and pp collisions is measured; • AuAu spectra fit well to an exponential function, while pp results fit well to a power law function; • dN/dy of f scales linearly with number of charged particles; • dN/dy and inverse slope measurement shows boost invariance for f within |y|<1.0; • 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?
0-5% 0-10% 10-30% 30-50% 50-80% pp Measured Mass