RHIC Strangeness Physics at intermediate and high pt

1. RHIC Strangeness Physics at intermediate and high pt R. Bellwied (Wayne State University) Is strangeness production in medium different than production in vacuum ? Strangeness Workshop, BNL, Feb.16-17,2006

2. Thanks to: Helen Caines,Richard Witt, Matt Lamont, Jana Bielcikova, Mark Heinz,Ying Guo, Camelia Mironov, Jeff Speltz, Sevil Salur, Wolf Holzmann (PHENIX)

3. The main topics Strangeness production through fragmentation in pp Nuclear suppression at high pT in AA Canonical Suppression at high pT from pp to AA Medium modification of fragmentation in AA Jets through strange two-particle correlations

4. Do we understand strangeness productionin elementary collisions ?Parton distribution functions (hep-ex/0305109) RHIC

5. pp at RHIC: Hadron formation in QCDNLO for heavy masses requires quark separation in fragmentation function ? z z In AA: is the fragmentation function modification due to the partonic medium universal ?

6. pp at RHIC:Strangeness formation in QCD(more on this tomorrow by Heinz, Strands and Werner) Strangeness production not described by leading order calculation (contrary to pion production). It needs multiple parton scattering (e.g. EPOS) or NLO corrections to describe strangeness production. Part of it is a mass effect (plus a baryon-meson effect) but in addition there is a strangeness ‘penalty’ factor (e.g. the proton fragmentation function does not describe L production). s is not just another light quark

7. Baryon production mechanism through strange particles correlations … • Test phenomenological fragmentation models OPAL ALEPH and DELPHI measurements: Yields and cosQ distribution between correlated pairs distinguishes between isotropic cluster (HERWIG) and non-isotropic string decay (JETSET) for production mechanism. Clustering favors baryon production JETSET is clearly favored by the data. Correlated L-Lbar pairs are produced predominantly in the same jet, i.e. short range compensation of quantum numbers.

8. Effects due to softer g-PDF and color factor No evidence for pQCD drop yet.

9. Are extensions of string models applicable in AA @ RHIC: e.g. EPOS++ (K.Werner, see talk tomorrow)

10. Flavor dependence of fragmentation in vacuum & medium Quark jets vs. gluon jets Leading particle asymmetries Baryon vs. meson asymmetries Particle vs anti-particle asymmetries Clustering

11. Why measure these effects with K and L instead of p and p ? Particle identification benefits from fact that the topological reconstruction method has no intrinsic momentum cut-off compared to dE/dx.

12. …but the use of rdE/dx might change that at least for inclusive measurements

13. Identified Particle RCP • strange RCP well behaved • all particles have same RCP for pT>~5 GeV: dominance of fragmentation? • no flavor dependence in fragmentation region ?

14. √sNN=200 GeV 0-5% 40-60% 0-5% 60-80% Baryon and meson suppression sets in at the same quark pT . Nuclear Modification Factor Rcp √sNN=200 GeV Y-4 L,K0s Strange RCP signals range of recombination model relevance Recombination scaling can be applied to RCP as well as v2

15. RCP double ratios independent of collision energy ! Recombination at SPS ?

16. Strangeness Production @ 62 GeV Increased baryon density, less energy density at 62 GeV: more in talk by Jeff Speltz

17. RAA of strange baryons A remarkable difference between RAA and RCP that seems unique to strange baryons. Ordering with strangeness content. ‘Canonical suppression’ is unique to strange hadrons This effect must occur ‘between’ pp and peripheral AA collisions

18. Flavor independence of RAA ? u,d dominated c,b dominated no flavor dependence in energy loss ??

19. Strange enhancement vs. charm suppression ? But is it a flavor effect ? Kaon behaves like D-meson, we need a charmed baryon

20. RAA - A mocked upstring picture does well(see V.Topor-Pop talk) Topor Pop et al. hep-ph/0505210 HIJING/BBar + KT ~ 1 GeV Strong Color Field qualitatively describes RAA. SCF - long range coherent fields SCF behavior mimicked by doubling the effective string tension SCF only produced in nucleus-nucleus collisions RAA≠ RCP

21. Flavor dependence of yield scaling PHENIX D-meson measurement • participant scaling for light quark hadrons • binary scaling for heavy flavor quark hadrons

22. Canonical suppression increases with increasing strangeness Strangeness yields from pp to AA LandX are not flat Production not well modeled by Npart (correlation volume)

23. s-quarks are formed primordial Scaling according to quark content? u, d – scale with Npart s,c,b – scale with Nbin Normalized to central data • p – Npart • K0s – 1/2*Npart + 1/2*Nbin • L – 2/3*Npart + 1/3*Nbin • – 1/3*Npart + 2/3*Nbin • f – Nbin • – Nbin D – Nbin Does strangeness “see” a different correlation volume ? Is a different phase space density required for strangeness production ?

24. Quark Scaled RAA of Strange Particles s-quarks scaled with NBin u&d-quarks scaled with Npart f scaled with N part

25. near-side away-side A+A flow+bkg p+p/d+Au Description of correlation functions • trigger/associated particles: charged particle or V0 (Λ, Λ, K0S) • correlation function (need to subtract elliptic flow in Au+Au)

26. 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

27. STAR preliminary Near side yield dependence on system size Large AA/pp ratio of near side associated yield Although within statistical errors all trigger particle species behave similarly, yield for “meson” triggered correlations appears to be systematically lower than for “baryon” triggers Why is yield increasing with Npart ? statistical errors only

28. 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: In Au+Au the thermal-shower recombination dominates

29. Recombination contribution is quark content dependent (R.Hwa, nucl-th/0602024)

30.     Alternate (?) or additional (?) explanation: long range  correlations in AuAu d+Au, 40-100% Jet-like correlation are on top of an additional flat long range correlation background in  • : cannot differentiate between the two correlations •  : additional correlation gets grouped into subtracted background STAR preliminary Au+Au, 0-5% 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

31. Big ridge effect within our acceptancein pT and h Most of the yield is due to the ridge. Preliminary result: after ridge subtraction: assoc. yield (pp) = assoc. yield (AA), no PID dep.

32. Particle species dependent correlations according to PHENIX Meson vs. Baryon trigger (for fixed Meson partner) Distribution of partner mesons per trigger-particle depends on trigger particle species in this pT range. Less energy available on same-side leads to smaller associated meson yield ?

33. Meson vs. Baryon partner (for fixed Meson trigger) Particle species dependent correlations according to PHENIX Away-side partner baryon to meson ratio ~2.5 times larger than near-side partner baryon to meson ratio for meson triggered correlations More energy available on the away-side leads to baryon production ?

34. Near side yield as f(pt(assoc)) 440+-7 MeV 403+-15 MeV 407+-16 MeV 460+-23 MeV instead of z = pThadron/pTparton use zT = pTassociated/pTtrigger (X.N.Wang: PLB 495 (2004)) Slope parameters in agreement with PHENIX For baryon/meson triggered associate yields

35. Summary Strange baryon production in pp requires multiple scattering (EPOS or NLO pQCD) High pt strange baryon production in AA enhanced instead of suppressed compared to pp . Is this due to simple canonical suppression ? Strange baryon does not scale with either Nbin or Npart. Do primordial strange quarks recombine with thermal light quarks and thus have a different correlation volume ? No strong flavor effects in high pt two particle correlations. Surprising absence of pQCD effects (gluon vs. quark contributions) Large associated particle yield in AA compared to pp. Might be due recombination or a long range Dh correlation or both. There might be a baryon/meson trend in agreement with recombination, but it is a small effect. Predictions for f and W need to be tested. VERY RICH PHYSICS IN THE STRANGENESS SECTOR @ RHIC