Jana Bielcikova (Yale University) for the STAR Collaboration 23 rd Winter Workshop on Nuclear Dynamics February 12-18, 2007 Two-particle correlations with strange baryons and mesons at RHIC

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 2 Outline: Physics motivation Correlations with identified strange trigger particles (Λ, Λ and K 0 S ) in d+Au and Au+Au collisions Correlations with identified strange associated particles (Λ, Λ and K 0 S ) in central Au+Au collisions Summary

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 3 R CP : intermediate p T : baryon/meson splitting independent of strangeness content high p T (p T > 5 GeV/c) : all particles have similar R CP and appear to show similar suppression large enhancement of baryon/meson ratio in central Au+Au relative to p+p collisions - reaches maximum at p T ~3 GeV/c jet fragmentation is not a dominant source of particle production Baryon/meson anomaly at intermediate p T

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 4 Parton recombination at intermediate p T in vacuo fragmentation of a high momentum quark to produce hadrons competes with in medium recombination of lower momentum quarks to produce hadrons 6 GeV/c particle via : fragmentation from high p T meson - 2 quarks at p T ~3 GeV/c baryon - 3 quarks at p T ~2 GeV/c Recombination produces more baryons than mesons at intermediate p T R.J. Fries et al., PRL 90 (202303) 2003 V. Greco et al., PRL 90 (202302) 2003 baryon meson

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 5 Jet-like correlations at RHIC central Au+Au 200 GeV: disappearance of away-side correlations observed at intermediate p T d+Au and p+p similar -> jet suppression is a final state effect lowering associated p T : - resurrects correlated yield at away side - near and away-side yields are enhanced with respect to d+Au 0.15<p T (assoc)<4.0 GeV/c 4 <p T (trig)<6 GeV/c 2 GeV/c <p T (assoc)<p T (trig)

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 6 Correlations with identified particles provide additional information on: baryon/meson enhancement medium modification of jet shape particle production mechanisms coalescence/recombination mechanisms and/or (modified) fragmentation of high-p T partons? parton hadrons Λ, Λ, K 0 S, γ … ? parton

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 7 Correlations at near-side   a.u. p T trig =3-6 GeV/c, 1.5 GeV/c <p T assoc < p T trig Au+Au 200 GeV  ridge    ridge jet jet+ridge after v 2 subtraction jet ridge v 2 + away-side peak h-h Au+Au: long-range  correlations at near side (“the ridge”) Near-side yield : Δɸ (J+R) = Δɸ (J) + Δɸ (R) Jet yield : Δɸ (J) = Δɸ (|Δη| 0.7) Ridge yield : Δɸ (R) = Δɸ (J+R) - Δɸ(J)

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 8 before elliptic flow subtraction Correlations with 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 Correlation function: normalized per trigger particle corrected for reconstruction efficiency of associated charged particles acceptance corrected STAR preliminary trigger: baryon/meson baryon/antibaryon after elliptic flow subtraction (using ZYAM method) Ajitanand et al, PRC72 (2005) systematic errors due to v 2 uncertainty ~ 30%

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 9 steep increase of near-side yield with centrality in Au+Au ratio of yields in central Au+Au/d+Au ~ 4-5 -> “jet” yield is independent of centrality and agrees with d+Au (effects of merged tracks under study) JetJet + Ridge -> “ridge” yield increases with centrality ridge of K 0 S < ridge of Λ Ridge Centrality dependence of near-side yield Jet

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 10 p T trigger dependence of jet and ridge yields near-side associated yield is ridge dominated at intermediate p T jet yield: - increases steeply with p T trigger - smaller for Λ-triggers than for K 0 S -triggers ? - baryon jet is wider than meson jet - effects of merged tracks under study jet/ridge ratio increases with p T trigger Jet + Ridge Ridge Jet

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 11 p T -distribution of associated particles Trigger particleT(ridge) MeVT (jet) MeV h +/- 438 ± 4 (stat.)478 ± 8 K0SK0S 406 ± 20 (stat.)530 ± 61 Λ 416 ± 11 (stat.)445 ± 49 STAR preliminary “jet” slope ridge slope inclusive slope J. Putschke (STAR), QM’06 h-h correlations p T associated >2GeV/c Ridge spectra similar to particles from the bulk Jet spectra are harder (T increases steeply with p T trig )

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 12 central-to-peripheral ratio (“I CP ”): - ~ 3 at p T associated = 1 GeV/c - decreases slowly with p T associated - jet yield is independent of centrality  “I CP ” is driven by long-range Δη correlations qualitative agreement with the parton recombination model BUT! quantitative agreement requires same centrality and p T selection check required on how well the “ridge” is reproduced by the model call for predictions for identified particles What does a parton recombination model predict? jet ReCo: R. Hwa, Z.Tan: PRC72 (057902) 2005

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 13 Particle composition in the ridge  /K 0 S ratio: in the ridge: ~ 1.0  similar to that from inclusive p T spectra in the jet: ~ 0.5  consistent with p+p |Δη|<2.0 |Δη|<0.7 STAR preliminary

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 14 What is the origin of the ridge ? 1) Parton radiation and its coupling to the longitudinal flow gluon bremsstrahlung of hard-scattered parton  parton is shifted to lower p T radiated gluon contributes to broadening 2) Medium heating + parton recombination Chiu & Hwa Phys. Rev. C72:034903,2005 hard parton passing through the medium  enhanced thermal parton distribution ( Δ T=15 MeV)  recombination of thermal partons forms a pedestal (ridge) pedestal is not a part of the jet enhanced baryon/meson ratio 3) Radial flow + trigger bias S.Voloshin, nucl-th/ , Nucl. Phys. A749, 287 (2005) 4) Longitudinal broadening of quenched jets in turbulent color field A. Majumder, B. Mueller, S.A.Bass, hep-ph/ plasma instabilities in expanding medium  broadening of jet cone  wide ridge in rapidity at low p T assoc Armesto et al, PRL 93 (2004)

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 15 Correlations with strange trigger particles: - system size: strong increase (~4-5) of the near-side yield in central Au+Au in comparison to d+Au collisions due to long-range Δη correlations ( “ ridge ” ). Ongoing studies of correlations in Cu+Cu. - ridge yield: steep increase with centrality, slope of p T spectra similar to that of “ bulk ” - jet yield: consistent with d+Au, constant with centrality, increasing with p T trigger Correlations with strange associated particles: B/M ratio in the ridge: close to the bulk B/M ratio in the jet: consistent with p+p The data qualitatively agree with recombination picture, but more detailed comparisons are needed to draw final conclusions. Summary

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 16 BACKUP

Jana Bielcikova23rd Winter Workshop on Nuclear Dynamics 17 Analysis method   raw data correlationmixed events correlationcorrected data correlation h-K 0 S, 3 < p T trig < 6 GeV/c, 2 < p T assoc < 3 GeV/c     ridge jet Au+Au, 0-10%