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High-p T strange particle spectra and correlations in STAR

This presentation discusses the baryon/meson enhancement and RCP at √sNN=200 GeV, azimuthal correlations of high-pT particles, and recent ReCo model predictions. It also explores the jet+ridge phenomenon and correlations of identified particles at high-pT.

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High-p T strange particle spectra and correlations in STAR

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  1. High-pT strange particle spectra and correlations in STAR Jana Bielcikova (Yale University) for the STAR Collaboration Hard Probes, Asilomar, California June 9-16, 2006

  2. Outline: • Baryon/meson enhancement and RCP at √sNN=200 GeV • Azimuthal correlations of h, Λ, Λ and K0S in d+Au and Au+Au collisions at √sNN=200 GeV • Test of recent ReCo model predictions (Ω/f ratio, Ω triggered correlations) • Conclusions Hard Probes 2006

  3. Baryon/meson enhancement a large enhancement of baryon/meson ratio in Au+Au relative to p+p at √sNN=200 GeV Year2 data: the enhancement reaches maximum at pT~3 GeV/c Year4 data (high statistics) : Λ/K0S ratio approaches p+p for pT> 5 GeV/c jet fragmentation is not a dominant source of particle production for pT=2-5 GeV/c Hard Probes 2006

  4. Baryon/meson enhancement: model comparisons SOFT+QUENCH: Gyullassy, Levai, Vitev, PRL 85 (2000), Nucl.Phys. A 715, 779 (2003) TEXAS: Greco, Ko, Levai, PRL 90 (2003), DUKE: Fries, Mueller, Nonaka, Bass, PRC 68 (2003) OREGON: Hwa, Yang, PRC 67, 034902 (2003) Both, soft+quench and recombination type of models, predict a peak in Λ/K ratio, however they can’t reproduce the peak location in pT, its magnitude and shape in detail. Hard Probes 2006

  5. RCP at √sNN=200 GeV • Year2: - baryon/meson difference at intermediate pT = 2-5 GeV/c • Year4: - extends the RCP to higher pT - strange and non-strange particles are consistent - appear to show a similar suppression at pT> 5 GeV/c Hard Probes 2006

  6. hadrons Λ, Λ,K0S,γ … ? parton parton hadrons Λ, Λ,K0S,γ … ? Identified correlations at medium/high pT • identified correlations at high-pT can provide additional information on: • jet quenching • baryon/meson enhancement at RHIC • particle production mechanisms coalescence/recombination mechanisms and/or (modified) fragmentation of high-pT partons? • pT dependence of trigger particle species Λfrom q-jet and g-jet, Λ from g-jet only Hard Probes 2006

  7. jet+ridge near-side away-side  A+A   flow+bkg p+p,d+Au jet ridge  ridge Azimuthal correlations - method near-side peak corresponds to intra-jet correlations away-side peak corresponds to inter-jet correlations This talk is only about the near-side peak ! Note: there are additional long-range η correlations (“ridge”) in Au+Au collisions (see talk by J. Putschke (STAR) ) Jet+Ridge yield : Δɸ(J+R) Jet yield : Δɸ(J) = Δɸ(Δη < 0.5) –Δɸ(Δη > 0.5) Ridge yield : Δɸ(R) = Δɸ(J+R) - Δɸ(J) Hard Probes 2006

  8. Correlation functions for strange particle triggers in Au+Au at 200 GeV trigger: baryon/meson baryon/antibaryon STAR preliminary STAR preliminary • Selection criteria: • 3.0 GeV/c < pTtrigger < 3.5 GeV/c • 1 GeV/c < pTassociated < 2 GeV/c • |h| < 1 • Corrections applied: • reconstruction efficiency • of charged particles • TPC sector boundaries STAR preliminary STAR preliminary correlation functions before elliptic flow subtraction correlation functions after elliptic flow subtraction syst. error due to v2 uncertainty ~ 25% Hard Probes 2006

  9. Jet + Ridge Ridge Jet STAR preliminary STAR preliminary STAR preliminary Centrality dependence of near-side associated yield in Au+Au Near-side associated yield rises with centrality -> “ridge” yield rises with centrality • -> “jet” yield is independent on centrality • jet yield for Λ < K0S <~ h ?, ridge yield: h ~ K0S < Λ ? Hard Probes 2006

  10. pTtrigger dependence of associated yield:d+Au vs Au+Au STAR preliminary STAR preliminary • within errors no dependence on trigger species (d+Au and Au+Au) • yield is ~ 3-4 times larger in Au+Au than in d+Au • Don’t forget: Au+Au is “ridge” dominated! • Let’s look on the jet yield separately Hard Probes 2006

  11. Jet + Ridge Ridge Jet STAR preliminary STAR preliminary STAR preliminary pTtrigger dependence of jet and ridge yield • near-side yield is ridge dominated (~constant for pTtrigger > 2.5 GeV/c) • jet yield rises steeply with increasing pTtrigger • jet/ridge ratio varies between ~ 10-30% with increasing pTtrigger • Λ-trigger charged associations < for K0S-triggers • Does baryon trigger take more energy away from jet than meson ? Hard Probes 2006

  12. pT distribution of associated particles J/R~10-15% Jet+ridge Jet only STAR preliminary STAR preliminary Hard Probes 2006

  13. What does a parton recombination model predict? Au+Au @ 200 GeV 3GeV/c<pTtrigger<6GeV/c STAR R. Hwa, Z.Tan: nucl-th/0503060 STAR preliminary • central-to-peripheral ratio of near-side associated yield is: • - ~ 3 at pTassoc = 1 GeV/c • - decreases slowly with pTassoc • qualitative agreement between the parton recombination model and the data • BUT! • a quantitative agreement requires same centrality and pT selection • check required on how well the “ridge” is reproduced by the model Hard Probes 2006

  14. Recent ReCo Model Predictions The production of f and Ω is almost exclusively from thermal s-quarks even out to 8 GeV/c (shower ”S” contributions are strongly suppressed) Observables: 1. The ratio of Ω/f yields should rise linearly with pT 2. Ω or f di-hadron correlations should be swamped by the background and not observed R. Hwa , nucl-th/0602024 Hard Probes 2006

  15. STAR Preliminary STAR Preliminary Ω/f ratio QM’05 SQM’06 • A qualitative agreement with model for pT < 4 GeV/c • Need more data to draw conclusions for pT > 4 GeV/c Hard Probes 2006

  16. Ω-charged correlations STAR preliminary • Not corrected for: efficiency, TPC sector boundaries, flow • Within statistical errors we can’t exclude existence of • near-side peak in Ω triggered correlations. • We expect ~ 8-10 more statistics for Ω, so stay tuned . Hard Probes 2006

  17. Conclusions • Strong baryon/meson enhancement in Au+Au over p+p • at √sNN=200 GeV observed for pT=2-5 GeV/c. • Identified RCP shows a baryon/meson splitting for pT=2-6 GeV/c, • but for pT> 6 GeV/c baryons and mesons are similarly suppressed. • Azimuthal correlations of identified strange (Λ and K0s) trigger particles associated with charged particles at moderately high-pT show: • - significant contribution from long range η correlations, • - ridge yield is rising with centrality • - jet yield is constant with centrality and rises with pTtrigger, • - indication of a lower associated jet yield for baryon triggers • than for meson triggers. • Within statistical errors, the Ω/ɸ ratio is consistent with • being constant and for Ω triggered correlations we can’t • exclude existence of near-side peak. • (more data to come ) Hard Probes 2006

  18. BACKUP Hard Probes 2006

  19. RCP at √sNN=200 GeV • Identified RCP from Year2 shows a clear difference between baryons and mesons at intermediate pT = 2-5 GeV/c • The Φ and K* clearly follow the mesons and not the baryons, it is not a mass effect ! 200 GeV 0-5% 40-55% Hard Probes 2006

  20. Identified correlations from PYTHIA Pythia 6.4 (untuned) Default PYTHIA 6.4 is a leading-order calculation: does not describe well inclusive pT-spectra of strange particles (Λ,Ξ, Ω…) NLO contributions can be simulated by introducing a K-factor the mixture of q+q, q+g and g+g processes is changed: -> it becomes more “gluon”-like Pythia 6.4 (K-factor=3) Hard Probes 2006

  21. Comparison of pTtrigger dependence of jet yield in PYTHIA and d+Au STAR preliminary • near-side yield rises slowly with pTtrigger • default Pythia shows a different behaviour for anti-Λ, • but yield agrees well with d+Au • Pythia with K-factor=3: all particle species behave similarly • as in the data, but the yield is a factor 2 higher • (because too many pions are generated with K-factor=3) • near-side yield rises slowly with pTtrigger • default Pythia shows a different behaviour for anti-Λ, • but yield agrees well with d+Au Hard Probes 2006

  22. Au+Au @ 200 GeV, (0-5)% 3<pTtrigger<4 GeV/c pT distribution of associated charged particles at near-side J. Ulery (STAR), QM2005 STAR Preliminary • 50% p+pbar • 95% π • charged 1/NtriggerdN/dpT STAR preliminary pTassociated (GeV/c) • spectral shape is similar for various trigger particle species • within errors Hard Probes 2006

  23. L K0S pT>2GeV/c pT>2GeV/c mass (GeV/c2) mass (GeV/c2) Strange particle identification in STAR Identification of strange particles: V0-decay vertices: Λ p + p- BR 64% Λ p + p+ K0Sp+ + p- BR 68% • Cuts on dE/dx of daughter particles • Topological cuts -> a very good S/B ratio  Hard Probes 2006

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