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Strange and Non-Strange Particle Ratios as a Function of p T and centrality in STAR at RHIC

Strange and Non-Strange Particle Ratios as a Function of p T and centrality in STAR at RHIC. B. Norman, Kent State University, and the STAR Collaboration. Outline. Physics Motivation Particle identification Topological ID of K +/- (kinks) Ring Imaging CHerenkov detector (RICH)

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Strange and Non-Strange Particle Ratios as a Function of p T and centrality in STAR at RHIC

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  1. Strange and Non-Strange Particle Ratios as a Function of pTand centrality in STAR at RHIC B. Norman, Kent State University, and the STAR Collaboration

  2. Outline • Physics Motivation • Particle identification • Topological ID of K+/- (kinks) • Ring Imaging CHerenkov detector (RICH) • Charged Kaons • K-/K+ ratio • High pT behavior • Particle Ratios • p/p, L/L • Model agreement

  3. Physics Motivation • Particle ratios probe: • Strangeness enhancement • K/p ~ s/d, s/d • Net baryon density • p/p, L/L ~ u/u, d/d • Gluon / Quark fragmentation regimes • p/p , L/L ~ glue/(quark + glue) • Medium opacity • K/p, p/p , L/L, RAA

  4. Traditional V0-like analysis with DCA cuts and kinematic analysis Kink PID For example, Kaon decays: K →m + n K+/- → π+/- + π0 Pion contamination: π →m + n Kinks = one prong decays

  5. Efficiency = Nfound / Ndecayed Acceptance = Ndecayed / Ntotal K- efficiency & acceptance

  6. STAR 200 GeV Au-Au PRELIMINARY Kink K- (|y|<0.5) dE/dx K- (|y|<0.1) Kinks dramatically increase momentum range of identified Kaons

  7. RICH PID Allows identification of particles to much higher momentum than dE/dx measurements in the TPC. 1 < p < 3 GeV/c for K+-, p+- 1.5 < p < 5 GeV/c for p, p

  8. dE/dx STAR p+p Kinks STAR 200 GeV Au-Au PRELIMINARY K-/K+ SPS/NA49 Very little dependence of K-/K+ ratio on centrality AGS/E866 dNp-/dy

  9. High momentum charged Kaons do not seem to follow a simple thermal (exponential) trend. They are more consistent with a (pQCD-inspired) power law. STAR 200 GeV Au-Au PRELIMINARY

  10. Little pT dependence: any high pT effects are present in both charges STAR 200 GeV Au-Au PRELIMINARY

  11. TPC de/dx RICH Systematic decrease in baryon/anti-baryon ratio with pT begins fairly early, not seen in the Kaons. STAR 200 GeV Au-Au PRELIMINARY

  12. Decrease in AntiBaryon/Baryon ratio at low (2-3 GeV/c) pT in agreement with pQCD predictions Onset of quark-dominated production??? p/p soft+quench

  13. If no “effects”: R < 1 in regime of soft physics R = 1 at high-pt where hard scattering dominates High pT K+- suppression • Nuclear modification factor RAA measures how AA spectra scales relative to pp. • Using only Au-Au data, we can approximate RAA using peripheral collision data, which have similar features to p-p (i.e., they scale with the number of binary collisions at higher momenta)

  14. STAR 200 GeV Au-Au PRELIMINARY Binary Collision Scaling K+ +K- N Participant Scaling 0-5% / 40-60% centrality 0-5% / 60-80% centrality Central charged Kaons show systematic suppression at high pT consistent with other particle spectra. (See Hui Long’s STAR talk) Suppression may be due to partonic energy loss?

  15. Conclusions • Baryon/anti-baryon ratios decrease at higher pT: not inconsistent with the trend of pQCD • Charged Kaons exhibit strong suppression at high pT in central data, a common trend in hadrons at RHIC.

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