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High-p T azimuthal correlations of neutral strange baryons and mesons in STAR at RHIC

High-p T azimuthal correlations of neutral strange baryons and mesons in STAR at RHIC. Jana Bielcikova (Yale University) for the STAR Collaboration PANIC ’05, Santa Fe, October 24-28, 2005. Motivation: high-p T processes at RHIC energy

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High-p T azimuthal correlations of neutral strange baryons and mesons in STAR at RHIC

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  1. High-pT azimuthal correlations of neutral strange baryons and mesons in STAR at RHIC Jana Bielcikova (Yale University) for the STAR Collaboration PANIC ’05, Santa Fe, October 24-28, 2005 Motivation: high-pT processes at RHIC energy Azimuthal correlations of Λ, Λ and K0Swith hadrons in d+Au and Au+Au collisions at √sNN=200 GeV (Yr 4) Centrality, pT and zT dependence of near-side associated yield Summary

  2. High-pT processes in Au+Au collisions STAR, PRL 91 (2003) 072304 central Au+Au collisions @ 200 GeV: • suppression of inclusive pT spectra with respect to p+p and d+Au collisions • disappearance of back-to-back correlations observed at high-pT PANIC '05, Santa Fe

  3. hadrons Λ, Λ,K0S,γ … ? parton parton hadrons Λ, Λ,K0S,γ … ? Identified correlations at high pT • identified correlations at high-pT can provide additional information on: • jet quenching • baryon/meson “puzzle” at RHIC • particle production mechanisms coalescence/recombination mechanism 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 ? • gamma jets ? PANIC '05, Santa Fe

  4. Lambda Anti-Lambda mass (GeV/c2) mass (GeV/c2) K0S 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 daughters • Topological cuts pT>2GeV/c pT>2GeV/c pT>2GeV/c PANIC '05, Santa Fe

  5. Correlation functions for strange particle triggers in Au+Au at 200 GeV trigger: baryon/meson particle/antiparticle 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 PANIC '05, Santa Fe

  6. STAR preliminary Do we see a difference between strange meson/baryon triggers in Au+Au ? • Although within statistical • errors all trigger particle • species behave similarly, • there is a hint of a trend: • yield for “meson” triggered • correlations appears to be • systematically lower than • for “baryon” triggers statistical errors only PANIC '05, Santa Fe

  7. pTtrigger dependence of associated yield J. Ulery (STAR), QM2005 STAR preliminary STAR preliminary • yield is ~ 3-4 times larger in Au+Au than in d+Au: • within statistical errors the associated yield in d+Au and Au+Au does not depend on type of trigger particle PANIC '05, Santa Fe

  8. 50% p+pbar • 95% π • charged STAR Preliminary Au+Au @ 200 GeV, (0-5)% 3<pTtrigger<4 GeV/c pT distribution of associated charged particles at near-side J. Ulery (STAR), QM2005 1/NtriggerdN/dpT STAR preliminary pTassociated (GeV/c) • spectral shape is similar for various trigger particle species PANIC '05, Santa Fe

  9. R. Hwa, Z.Tan: nucl-th/0503060 Au+Au d+Au STAR preliminary What does a parton recombination model predict? Au+Au @ 200 GeV 3GeV/c<pTtrigger<6GeV/c • the ratio of near-side associated yield in central/peripheral Au+Au • collisions is ~ 3 at pTassociated = 1 GeV/c and decreases slowly • with increasing pTassociated • data are in a good agreement with predictions from • a parton recombination model: • Au+Au: thermal-shower recombination dominates PANIC '05, Santa Fe

  10. zT dependence hadrons Λ, Λ,K0S,γ … ? parton parton hadrons Λ, Λ,K0S,γ … ? • Fragmentation: • z = pThadron/pTparton • X.N.Wang: PLB 495 (2004) : • hadron-triggered fragmentation • functions Dh1h2(zT), where • zT = pTassociated/pTtrigger • in our case h1 is identified particle Fragmentation functions for various trigger particle species agree within statistical errors. PANIC '05, Santa Fe

  11. Summary • we have measured azimuthal correlations using identified strange trigger particles (Λ, Λ, K0s) and associated charged particles at moderately high-pT • we have studied centrality, pT and zT dependencies of associated near-side yield: • no significant difference between trigger particle species • in the studied pT range observed, although data suggest that • there might be a baryon/meson/mass difference • data agree well with parton recombination model • there are many open questions left: • What is the origin of these correlations ? • Is there baryon and meson difference ? • Is the fragmentation modified ? -> study of away-side peak • There are ~50% more central events on tape  • … to be continued PANIC '05, Santa Fe

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