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K*(892) Resonance Production in Au+Au and p+p Collisions at s NN =200GeV

K*(892) Resonance Production in Au+Au and p+p Collisions at s NN =200GeV. Haibin Zhang Yale University for the STAR Collaboration. Outline: Motivation STAR Data Analysis and Results Conclusions. 1. Motivation I: Why measure K*?.

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K*(892) Resonance Production in Au+Au and p+p Collisions at s NN =200GeV

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  1. K*(892) Resonance Production in Au+Au and p+p Collisions at sNN=200GeV Haibin Zhang Yale University for the STAR Collaboration • Outline: • Motivation • STAR Data • Analysis and Results • Conclusions Haibin Zhang, SQM 2003 1

  2. Motivation I: Why measure K*? K* lifetime ~4fm/c, comparable to lifetime of the hot dense matter (few fm/c)  sensitive to the properties of hot dense matter K* Mass and width modification and the line shape in-medium dynamical effects Compared to other particles (K*/K)  information (timing) on chemical freeze-outandthermal freeze-out conditions K*/, /K*  information on strangeness enhancement Event-Mixing Technique Measuring K* hadronic decay channel: K*0K+ K*±KS0± Haibin Zhang, SQM 2003 2

  3. K* Daughter particles’ Rescattering Effect destroys part of K* signal K* lost  K K*   K* Regeneration Effect compensates K* yield K K K K* measured K*/K reveals timing between chemical and thermal freeze-out Motivation II: K* Survival Probability K* thermally produced at the chemical freeze-out stage  K* K K* measured Thermal freeze-out Chemical freeze-out time Haibin Zhang, SQM 2003 3

  4. STAR year-II Data, sNN=200GeV Au+Au minbias data: ~2.0M events with 4 centrality bins: 0%-10%, 10%-30%, 30%-50%, 50%-80% Au+Au top 10% central trigger data: ~1.8M events p+p data: ~6.0M events Track Momentum Cuts Au+Au: Kaon 0.2<p<10.0GeV/c, Pion 0.2<p<10.0GeV/c  increase statistics  Particle mis-identification Kaon Clean PID Cut for p+p data p+p: Kaon 0.2<p<0.7GeV/c Pion 0.2<p<10.0GeV/c Kaon Clean PID cut  minimize particle mis-identification STAR Data and Cuts Haibin Zhang, SQM 2003 4

  5. K*0 from Au+Au Collisions at 200GeV K*0 STAR Preliminary K*0 peak invisible in same event spectra before background subtraction P-Wave Breit-Wigner function + Linear Background Background comes from mis-identified particles and elliptic flow effect Haibin Zhang, SQM 2003 5

  6. K*0 from p+p Collisions at 200GeV STAR Preliminary K*0 peak visible in same event spectra before background subtraction P-Wave Breit-Wigner function Haibin Zhang, SQM 2003 6

  7. p+p Collisions Au+Au 50%-80% K*± from Au+Au and p+p Collisions at 200GeV STAR Preliminary K* peak observed both in Au+Au 50%-80% centrality bin and p+p collisions Need acceptance and efficiency corrections for transverse mass spectra Haibin Zhang, SQM 2003 7

  8. STAR Preliminary K*0 Mass and Width Distribution K*0 Mass shift in p+p and Au+Au at low pT possible in-medium dynamic effect modified K*0 mass and the line shape K*0 width matches the MC prediction Haibin Zhang, SQM 2003 8

  9. (K*0+K*0)/2  increase statistics Exponential Fit function: K*0 yield dN/dy and Inv. Slope T with statistical errors extrapolated from fit function STAR Preliminary Systematic errors: dN/dy in Au+Au: 15%, in p+p: 6% InvSlp in Au+Au: 11%, in p+p: 4% K*0 Transverse Mass Spectra Haibin Zhang, SQM 2003 9

  10. dN/dy in Au+Au collisions are increasing “linearly” vs. number of charged particles Inverse slope in Au+Au collisions is larger than in p+p collisions Inverse slope in Au+Au collisions is “flat” vs. number of charged particles STAR Preliminary K*0 dN/dy and Inv. Slope vs. Centrality Haibin Zhang, SQM 2003 10

  11. K*0 <pT> in Au+Au collisions is larger than in p+p collisions K*0 <pT> in peripheral Au+Au collisions is larger than anti- proton <pT>  Rescattering? K*0 <pT> in central Au+Au collisions is comparable toanti- proton <pT>  Rescattering + Regeneration? K*0 <pT> in Au+Au collisions is “flat” vs. number of charged particles STAR Preliminary K*0 <pT> vs. Centrality Haibin Zhang, SQM 2003 11

  12. K*0/K in AuAu is a factor of 2 larger than in STAR pp  rescattering /K*0 increasing vs. s  strangeness enhancement or rescattering? Particle Ratios STAR Preliminary Haibin Zhang, SQM 2003 12

  13. K*(892) resonance production has been measured at sNN=200GeV from both Au+Au and p+p collisions at STAR K*0 mass shift at low pT has been observed from both Au+Au and p+p collisions K*0 dN/dy in Au+Au are “linearly” increasing vs. number of charged particles, inverse slope in Au+Au is larger than in p+p K*0 <pT> measured from Au+Au and p+p collisions and compared to identified particles, K, p Summary K*0/K ratio and <pT> daughter particles’ rescattering /K*0 strangeness enhancement or rescattering effect? Haibin Zhang, SQM 2003 13

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