1. What can we learn from high-p T azimuthal correlations of neutral strange baryons and mesons at RHIC ? Jana Bielcikova (Yale University) for the STAR Collaboration Hot Quarks, Sardinia, Italy, May 15-20, 2006

2. Jana Bielcikova (Yale)Hot Quarks 20062 Outline: Motivation: high-p T processes at RHIC energy Azimuthal correlations of h, Λ, Λ and K 0 S in d+Au and Au+Au collisions at √s NN =200 GeV Centrality and p T dependence of near-side associated yield PYTHIA predictions Summary

3. Jana Bielcikova (Yale)Hot Quarks 20063 High-p T processes at RHIC energy central Au+Au collisions @ 200 GeV: suppression of inclusive p T spectra with respect to p+p and d+Au disappearance of back-to-back correlations observed at high-p T d+Au and p+p similar -> jet suppression is not initial state effect lowering associated p T resurrects correlated yield 0.15<p T (assoc)<4.0 GeV/c2 GeV/c <p T (assoc)<p T (trig) 4 <p T (trig)<6 GeV/c

4. Jana Bielcikova (Yale)Hot Quarks 20064 Intermediate p T baryon/meson enhancement Au+Au 0-10% p+p large enhancement of baryon/meson ratio in central Au+Au relative to p+p reaches maximum at p T ~3 GeV/c jet fragmentation is not a dominant source of particle production

5. Jana Bielcikova (Yale)Hot Quarks 20065 Identified correlations at medium/high p T identified correlations at high-p T can provide additional information on: jet quenching baryon/meson enhancement at RHIC particle production mechanisms coalescence/recombination mechanisms and/or (modified) fragmentation of high-p T partons? p T dependence of trigger particle species Λ from q-jet and g-jet,  Λ from g-jet only -> see also talks by Joern Putschke and Leon Gaillard parton hadrons Λ, Λ, K 0 S, γ … ? parton

6. Jana Bielcikova (Yale)Hot Quarks 20066 Strange particle identification in STAR Identification of strange particles: – –V0-decay vertices: Λ  p +  - BR 64% Λ  p +  + K 0 S   + +  - BR 68% LambdaAnti-Lambda mass (GeV/c 2 ) K0SK0S Cuts on dE/dx of daughters Topological cuts p T >2GeV/c

7. Jana Bielcikova (Yale)Hot Quarks 20067 correlation functions before elliptic flow subtraction correlation functions after elliptic flow subtraction syst. error due to v 2 uncertainty ~ 25% Correlation functions for strange particle triggers in Au+Au at 200 GeV Selection criteria: 3.0 GeV/c<p T trigger <3.5 GeV/c 1 GeV/c<p T associated <2 GeV/c |  |<1 Corrections applied: reconstruction efficiency of charged particles TPC sector boundaries STAR preliminary trigger: baryon/meson baryon/antibaryon

8. Jana Bielcikova (Yale)Hot Quarks 20068 -> “ridge” yield rises with centrality -> “jet” yield is independent on centrality jet yield for Λ < K 0 S <~ h ?, ridge yield: h < K 0 S < Λ ? near-side yield rises with N part due to long range  correlations (“ridge”) “ridge” subtraction: correlation in  0.5 – correlation in  0.5 Centrality dependence of near-side associated yield in Au+Au STAR preliminary

9. Jana Bielcikova (Yale)Hot Quarks 20069 p T trigger dependence of associated yield: d+Au vs Au+Au within statistical errors the associated yield in d+Au and Au+Au does not depend on type of trigger particle, although in Au+Au there is a hint of a trend of a baryon/meson difference yield is ~ 3-4 times larger in Au+Au than in d+Au Don’t forget: in Au+Au we are “ridge” dominated! Let’s look on the jet yield separately STAR preliminary

10. Jana Bielcikova (Yale)Hot Quarks 200610 p T trigger dependence of jet yield STAR preliminary to extract jet yield p T trigger behaviour, p T assoc >1.5 GeV/c has been used as for the centrality figure (p T assoc >1 GeV/c needed for d+Au comparison due to limited statistics) jet yield rises with increasing p T trigger yield for Λ triggers appears to be systematically below that for charged and K 0 S triggers

11. Jana Bielcikova (Yale)Hot Quarks 200611 Identified correlations from PYTHIA Pythia 6.4 (untuned) Pythia 6.4 (K-factor=3) Default PYTHIA 6.4 is a leading-order calculation: does not describe well inclusive p T -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 the mixture of q+q, q+g and g+g processes is changed: -> it becomes more “gluon”-like

12. Jana Bielcikova (Yale)Hot Quarks 200612 Comparison of p T trigger dependence of jet yield in PYTHIA and d+Au near-side yield rises slowly with p T trigger 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) STAR preliminary near-side yield rises slowly with p T trigger default Pythia shows a different behaviour for anti-Λ, but yield agrees well with d+Au

13. Jana Bielcikova (Yale)Hot Quarks 200613 p T distribution of associated charged particles at near-side spectral shape is similar for various trigger particle species within errors Au+Au @ 200 GeV, (0-5)% 3<p T trigger <4 GeV/c 50% p+pbar 95% π charged 1/N trigger dN/dp T p T associated (GeV/c) STAR Preliminary J. Ulery (STAR), QM2005 STAR preliminary

14. Jana Bielcikova (Yale)Hot Quarks 200614 p T distribution of associated particles STAR preliminary Jet+ridge Jet only STAR preliminary Trigger particleT (jet) MeVT (jet+ridge) MeV Charged511 ± 6450 ± 3 K0SK0S 539 ± 58456 ± 13 Λ522 ± 84430 ± 8 J/R~10-15%

15. Jana Bielcikova (Yale)Hot Quarks 200615 STAR preliminary What does a parton recombination model predict? the ratio of near-side associated yield in central/peripheral Au+Au collisions is ~3 at p T assoc =1 GeV/c and decreases slowly with p T assoc data are in a qualitative agreement with predictions from a parton recombination model BUT! a quantitative agreement requires the same centrality selection and to account for the “ridge” in pseudo-rapidity R. Hwa, Z.Tan: nucl-th/0503060 Au+Au Au+Au @ 200 GeV 3GeV/c<p T trigger <6GeV/c

16. Jana Bielcikova (Yale)Hot Quarks 200616 We have measured azimuthal correlations of charged and identified strange (Λ and K 0 s ) trigger particles associated with charged particles at moderately high-p TWe have measured azimuthal correlations of charged and identified strange (Λ and K 0 s ) trigger particles associated with charged particles at moderately high-p T - in the studied p T range there is a significant contribution - in the studied p T range there is a significant contribution from long range pseudo-rapidity correlations (“ridge”) from long range pseudo-rapidity correlations (“ridge”) - ridge yield is rising with centrality - ridge yield is rising with centrality - jet yield is constant with centrality and rises with p T trigger - jet yield is constant with centrality and rises with p T trigger - indication of a lower associated jet yield for baryon triggers - indication of a lower associated jet yield for baryon triggers than for meson triggers than for meson triggers - the data are in a qualitative agreement with a parton recombination model - the data are in a qualitative agreement with a parton recombination model There is more to come on identified strange particle correlations: - identified strange associated particles - multi-strange particles, especially  triggers will be a crucial test of the recombination picture (there should be no correlation!) So, stay tuned Summary