1 / 15

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.

dmitri
Télécharger la présentation

Strangeness Production in Heavy-Ion Collisions at STAR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related