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Strangeness Production in Heavy-Ion Collisions at STAR

Strangeness Production in Heavy-Ion Collisions at STAR. Introduction.. Bulk strangeness production… Mid- p T spectra… Hard processes and strangeness… Summary…. Anthony Timmins for the STAR Collaboration. Introduction. STAR Preliminary.

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Strangeness Production in Heavy-Ion Collisions at STAR

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  1. Strangeness Production in Heavy-Ion Collisions at STAR • Introduction.. • Bulk strangeness production… • Mid-pT spectra… • Hard processes and strangeness… • Summary… Anthony Timmins for the STAR Collaboration

  2. Introduction STAR Preliminary • Strangeness production helps us explore many processes… • low q2 • Strangeness enhancement • Flow • Recombination • high q2 • Jet quenching • Flavor changing • New STAR data in this talk • Cu+Cu 62 GeV • High-pT p+p 200 GeV • High-pTAu+Au 200 GeV

  3. Bulk strangeness productionAs a QGP signature… • Strangeness enhancement key measurement at 200 GeV • Old idea (Phys. Rev. Lett. 48 (1982) 1066) • s+s production cross section increases in QGP • s+s in QGP reaches thermal expectations on small time scale… • s ~3 fm/c (QGP) • s ~20-200 fm/c (hadron gas) • Can it be understood via phase space restrictions? • Canonical Formalism • Strangeness in p+p suppressed relative to A+A? (Phys. Lett. B486 (2000) 61)

  4. f=1/4 Fraction of participants that undergo multiple collisions Multiple Collisions Single Collisions Bulk strangeness production Enhancement at 200 GeV… STAR Preliminary • New d+Au 200 GeV data (not shown) • See Xianglei Zhu’s talk later in session • Cu+Cu and Au+Au and enhancements (E) approximately described by simple function: • Predicts… • Rise in E with <Npart> • Higher E for central Cu+Cu • Above 1 E for d+Au 200 GeV • K0SB = 2.10 • B = 2.45 B = 5.05 B = 13.1

  5. Bulk strangeness production dN/dy at 62 GeV… New Cu+Cu 62 GeV data STAR Preliminary • No p+p 62 GeV reference data yet • Can still investigate dN/dy per <Npart> •  and K0Sper participant yields can be described by • C f(Npart) + D • Reproduces qualitative features of yields per <Npart> • Turning to multi-strange… Cu+Cu K0S and : Stat errors only Au+Au K0S and : Stat+Sys errors Cu+Cu  and : Stat errors only Au+Au  and : Stat errors only

  6. Bulk strangeness productionWhat about the ? • Enhanced in heavy-ion collisions at 62 and 200 GeV… •  has closed strangeness • Canonical Formalism predicts no enhancement… • Sits between Kaon and Lambda values at 200 GeV... • Also can be described by: arXiv:0810.4979v1 62 GeV B = 1.2 200 GeV B = 2.9

  7. Bulk strangeness productionWhat does this scaling mean? • Proposed by F. Becattini and J. Manninen to be indicative of core-corona effects (arXiv:0811.3766v1) • Participants with one collision = corona • Participants with multiple collisions = core • Strangeness equilibrated in core • B  particle density • Strangeness p+p like in corona • Alternative core-core model EPOS approximately reproduces scaling • As does AMPT (string+rescattering)….

  8. Mid-pT spectraBaryon/meson ratios at Au+Au 200 GeV… • Strange baryon/meson anomalies established at STAR • Quark coalescence? • Mid-pT baryon production preferable to meson production • Coalescence models reproduce qualitative features of ratios • p/ • /K0S • / • Predict turnover… • Fail to get pT position right… Sarah Blyth, Quark Matter 2006

  9. Mid-pT spectraBaryon/meson ratios at 62 GeV… STAR Preliminary • New Cu+Cu 62 GeV data… • High strange baryon/meson ratios observed for both systems • Coalescence occuring at lower energy?

  10. Mid-pT spectraComparisons to EPOS… STAR Preliminary • EPOS Core • Flow induced, gives higher mass particles pT kick at mid-pT Energy = 62 GeV 200 GeV • EPOS Corona • Dominates production at high-pT Are high baryon/meson ratios unique to coalescence?

  11. STAR preliminary pT (GeV/c) Hard processes and strangenessRAA of identifed particles… • New high-pT p+p and Au+Au 200 GeV data… • p+p shown Yichun Xu’s talk in Ridge Phenomena and Jet Flavor Conversion • Parton flavor conversion prediction (Phys. Rev. C77 (2008) 054902) • Hard scattered partons interact with medium, convert flavour • Boosts kaon RAArelative to pion RAA • Data consistent with conversion scenario…

  12. Hard processes and strangenessRAA vs. system size… • Measure integrated RAA for pT > 5.5 GeV/c • <pT> ~ 6.2 GeV/c • Ratio • Above one for all centralities • Strangeness enhancement at high-pT! • In particular, RAA (K) > RAA ()for Au+Au where <Npart> ~ 20 • Does parton flavor conversion happen in small systems? • Can we dismiss the Cronin effect? • Do we have to push higher in pTfor parton conversion searches? New high-pT p+p and Au+Au 200 GeV data…

  13. Summary • Bulk strangeness production • Enhancement for many particles appears to depend on fraction of participants that undergo multiple collisions • Expected in core-corona scenario • Also reproduced by AMPT • Mid-pT spectra • Coalescence typically describes trends • Core-corona+flow can also explain strange high baryon/meson ratios • Hard processes and strangeness • Hint of jet conversions in central Au+Au • Kaon RAA higher than pion RAA • Also applies to small systems • Can jet conversions happen there also? • Could other effects contribute?

  14. Hard processes and strangenessFlavor changing… • Prediction: hard scattered partons interact with medium, convert flavour • Boosts Kaon RAArelative to non-conversion scenario • Kaon RAA factor of two higher at RHIC • Excellent PID for K0S at STAR… • LHC predicts modest increase

  15. Mid-pT spectraQuark coalescence in AMPT… • Use particle ratios and constituent quark scaling • Extract shape of strange and up/down quark spectra • Use shapes as input for AMPT’s quark distributions • Run in coalescence mode… • Good description of ,  and  spectra in central Au+Au 200 GeV collisions • Shows quark spectra shapes can be extracted accurately… Phys. Rev. C 78 (2008) 034907

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