Strangeness Production in HeavyIon Collisions at STAR Anthony

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

2/13 Introduction o STAR Preliminary Strangeness production helps us explore many processes… – low q 2 o Strangeness enhancement o Flow o Recombination – high q 2 o Jet quenching o Flavor changing o New STAR data in this talk – Cu+Cu 62 Ge. V – High-p. T p+p 200 Ge. V – High-p. T Au+Au 200 Ge. V STAR

3/13 Bulk strangeness production As a QGP signature… o Strangeness enhancement key measurement at 200 Ge. V o 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… o o o s ~3 fm/c (QGP) s ~20 -200 fm/c (hadron gas) Can it be understood via phase space restrictions? – Canonical Formalism o Strangeness in p+p suppressed relative to A+A? (Phys. Lett. B 486 (2000) 61) STAR

4/13 Bulk strangeness production Enhancement at 200 Ge. V… o New d+Au 200 Ge. V data (not shown) – See Xianglei Zhu’s talk later in session o Cu+Cu and Au+Au and enhancements (E) approximately described by simple function: Multiple Collisions Single Collisions f=1/4 STAR Preliminary Fraction of participants that undergo multiple collisions o Predicts… – Rise in E with <Npart> – Higher E for central Cu+Cu – Above 1 E for d+Au 200 Ge. V K 0 S B = 2. 10 B = 5. 05 B = 13. 1 B = 2. 45 STAR

5/13 Bulk strangeness production d. N/dy at 62 Ge. V… STAR Preliminary o New Cu+Cu 62 Ge. V data No p+p 62 Ge. V reference data yet – Can still investigate d. N/dy per <Npart> o and K 0 Sper participant yields can be described by – C f(Npart) + D o Reproduces qualitative features of yields per <Npart> o Turning to multi-strange… Cu+Cu K 0 S and : Stat Cu+Cu errors and only : Stat errors only Au+Au K 0 S and : Stat+Sys Au+Au errors and : Stat errors only STAR

6/13 Bulk strangeness production What about the ? o Enhanced in heavy-ion collisions at 62 and 200 Ge. V… – has closed strangeness – Canonical Formalism predicts no enhancement… – Sits between Kaon and Lambda values at 200 Ge. V. . . o Also can be described by: ar. Xiv: 0810. 4979 v 1 62 Ge. V B = 1. 2 200 Ge. V B = 2. 9 STAR

7/13 Bulk strangeness production What does this scaling mean? o Proposed by F. Becattini and J. Manninen to be indicative of core-corona effects (ar. Xiv: 0811. 3766 v 1) – Participants with one collision = corona – Participants with multiple collisions = core o Strangeness equilibrated in core – B particle density o Strangeness p+p like in corona o Alternative core-core model EPOS approximately reproduces scaling – As does AMPT (string+rescattering)…. STAR

8/13 Mid-p. T spectra Baryon/meson ratios at Au+Au 200 Ge. V… o Strange baryon/meson anomalies established at STAR – Quark coalescence? o Mid-p. T baryon production preferable to meson production o Coalescence models reproduce qualitative features of ratios – p/ – /K 0 S – / o Predict turnover… – Fail to get p. T position right… Sarah Blyth, Quark Matter 2006 STAR

9/13 Mid-p. T spectra Baryon/meson ratios at 62 Ge. V… STAR Preliminary o New Cu+Cu 62 Ge. V data… o High strange baryon/meson ratios observed for both systems – Coalescence occuring at lower energy? STAR

10/13 Mid-p. T spectra Comparisons to EPOS… STAR Preliminary Energy = 62 Ge. V 200 Ge. V o o EPOS Corona EPOS Core – Dominates production at high-p. T – high Flow baryon/meson induced, gives higher massunique to coalescence? Are ratios particles p. T kick at mid-p. T STAR

11/13 Hard processes and strangeness RAA of identifed particles… o New high-p. T p+p and Au+Au 200 Ge. V data… – p+p shown Yichun Xu’s talk in Ridge Phenomena and Jet Flavor Conversion o Parton flavor conversion prediction (Phys. Rev. C 77 (2008) 054902) – Hard scattered partons interact with medium, convert flavour – Boosts kaon RAArelative to pion RAA STAR preliminary p. T (Ge. V/c) o Data consistent with conversion scenario… STAR

12/13 Hard processes and strangeness RAA vs. system size… o Measure integrated RAA for p. T > 5. 5 Ge. V/c – <p. T> ~ 6. 2 Ge. V/c o Ratio – Above one for all centralities – Strangeness enhancement at high-p. T! o 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 p. T for parton conversion searches? New high-p. T p+p and Au+Au 200 Ge. V data… STAR

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

14/13 Hard processes and strangeness Flavor changing… o Prediction: hard scattered partons interact with medium, convert flavour – Boosts Kaon RAArelative to non-conversion scenario o Kaon RAA factor of two higher at RHIC – Excellent PID for K 0 S at STAR… – LHC predicts modest increase STAR

15/13 Mid-p. T spectra Quark coalescence in AMPT… o Use particle ratios and constituent quark scaling – Extract shape of strange and up/down quark spectra o Use shapes as input for AMPT’s quark distributions – Run in coalescence mode… o Phys. Rev. C 78 (2008) 034907 Good description of , and spectra in central Au+Au 200 Ge. V collisions – Shows quark spectra shapes can be extracted accurately… STAR