A few observations on strangeness production at SPS and RHIC Outline Strangeness Enhancement – Measurement of entropy? RAA - Soft physics in the hard regime? RCP - Energy dependence mT distributions – Quark vs gluon jets
Strangeness enhancement The enhancements grow with the strangeness of the baryon and centrality. The enhancements show no linear dependence on Npart. The enhancements are close to those measured in √sNN =17.3 GeV collisions. See phase space suppression in p-p Solid – STAR Open – NA57 STAR Preliminary Not well modeled by theory
Sensitivity of calculation K. Redlich – private communication Correlation volume: V= AaNN·V0 ANN = Npart/2 V0 = 4/3p·R03 R0 = 1.1 fm proton radius/ strong interactions T= 170-177 MeV a= 1 Solid – STAR Open – NA57 STAR Preliminary Particle ratios indicate T= 165 MeV STAR Preliminary Can it explain energy independence?
Energy systematics - motivation from h- PHOBOS: Phys. Rev. C70, 021902(R) (2004) There’s a correlation between dNch/dh and Npart/2 small dotted lines are: dNch/dh = npp(1-x)Npart/2 + xNbin npp= Yield in pp = 2.29 ( 1.27) x = 0.13 N.B.: SPS energy only 17 GeV From npp can predict yield at any Npart
HBT and dNch/dh Scaling works across a large energy range HBT radii ~linear as a function Npart1/3 Even better in (dNch/dh)1/3 power 1/3 gives approx. linear scale Scaling works across a large energy range nucl-ex/0505014 M.Lisa et al.
Strangeness and dNch/dh Look at yields relative to pp SPS and RHIC data follows same curves as a func. of dNch/dη dNch/dη - strongly correlated to the entropy of the system! Entropy alone seems to drive much of the soft physics
Nuclear modification factors - RAA HIJING/BBar + KT ~ 1 GeV Strong Colour Field qualitatively describes RAA. SCF - long range coherent fields SCF behaviour mimicked by doubling the effective string tension SCF controlsqq and qqqq production rates and gs Topor Pop et al. hep-ph/0505210 SCF only produced in nucleus-nucleus collisions RAA≠ RCP Effects dominate out to high pT
Nuclear modification factors - RCP √sNN=62 GeV 0-5% 40-60% √sNN=200 GeV 0-5% 40-60% NA57, PLB in print, nucl-ex/0507012 √sNN=17.3 GeV First time differences between L and L B absorption? Recombination or different “Cronin” for L and K at SPS?
Gluon vs quark jets in p-p No absolute mT scaling – “data” scaled to match at mT~1 GeV/c Quark jets events display mass splitting Gluon jets events display baryon/meson splitting Way to explore quark vs gluon dominance
mT distributions of real data Again no complete scaling p-p Appears to be scaling at low mT STAR Preliminary p+p 200 GeV Dominated by gluon jets Au-Au Radial flow prevents scaling at low mT Seems to scale at higher mT – no meson/baryon difference Meson/baryon difference in the p-p not Au-Au
Summary Have gathered data for a very detailed study. Evidence that strangeness production driven by the entropy of the system created, not only by Npart. Evidence of phase space suppression out to high pT. RCP meson/baryon difference seen at SPS too. Starting exporation of strangeness role in fragmentation.
How does volume affect production? Canonical (small system i.e. p-p): Quantum Numbers conserved exactly. Computations take into account energy to create companion to ensure conservation of strangeness. Relative yields given by ratios of phase space volumes Pn/Pn’ = fn(E)/fn’(E) Grand Canonical limit (large system i.e. central AA): Quantum Numbers conserved on average via chemical potential Just account for creation of particle itself. The rest of the system “picks up the slack”. When reach grand canonical limit strangeness will saturate. Not new idea pointed out by Hagedorn in 1960’s (and much discussed since)
Predictions at higher energies Canonical suppression increases with increasing strangeness Canonical suppression increases with decreasing energy σ(Npart) / Npart = ε σ(pp) ε > 1 Enhancement!
But then at √s= 8.8 GeV NA57 (D. Elia QM2004) C to GC predicts a factor 4 - 5 larger X- enhancement at √sNN =8.8 GeV than at 17 GeV Perhaps yields don’t have time to reach limit – hadronic system?