Recent results on strangeness from the STAR experiment Matthew A. C. Lamont, Yale University for the STAR Collaboration Outline Bulk Measurements Outside the Bulk Production vs Energy Strangeness Enhancement Elliptic Flow p+p Collisions Identified Particle Ratios di-Hadron Correlations

SQM 2006: 2 STAR strangeness talks at SQM Φ-meson production and flow in HIC at RHIC - S Blyth Resonance studies with STAR - S Salur E-by-E fluctuations in the K/π ratio at RHIC - S Das Global polarization measurements in Au+Au - I Selyuzhenkov Strange hadron v 2 - M Oldenburg Studying the sapce-time structure of multi- strange baryons - P Chaloupka

SQM 2006: 3 Strange particles - we’ve got ‘em > 95% of all particle production occurs below 2 GeV/c in p T This region dominates the bulk properties of the system

SQM 2006: 4 Strange Particles vs Energy Smooth increase in strange baryon production from 17 GeV to 200 GeV Expected behaviour for ratios with decreasing net baryon density observed K/π also smooth and shows ~ 50% enhancement over p+p collisions at RHIC energies

SQM 2006: 5 Strangeness Enhancement at RHIC Enhancement at 200 GeV similar to SPS Thanks to K. Redlich !! Temperature variations from 165 to 170 MeV V = A α V 0 A = N part /2 V 0 = 4/3.πR 3 α = 1 - scales with Volume α = 2/3 - scales with Surface Area α = 1/3 - scales with Length Assuming a constant T chem : STAR NA57

SQM 2006: GeV Blast wave fits to data Strong centrality dependence on freeze out parameters for light hadrons Multi-strange hadrons freeze out earlier, with a lower Indicative of smaller cross-section for interactions of multiply strange hadrons with lighter species. Is this a signature of partonic collectivity?

SQM 2006: 7 The same scaling behaviour is observed in 62 GeV data v 2 of strange hadrons Talk: M. Oldenburg, Poster:Yan Lu v 2 (p T ) p T [GeV/c] Mass ordering observed at lower p T v 2 saturates for p T > 3 GeV/c Clear baryon/meson difference at intermediate to high p T observed New, high statistics measurement shows deviation from ideal scaling...

SQM 2006: 8 v 2 of multi-strange hadrons Hydro: P. Huovinen, private communication Talks: M. Oldenburg S-L Blyth Poster: Yan Lu Multi-strange hadrons flow just as well as other baryons and mesons Collective flow is developed early, during partonic stage Strange quarks flow like the light quarks....

SQM 2006: 9 Moving away from the bulk... Strangeness at intermediate and high-p T in Au+Au collisions Strangeness in p+p collisions

SQM 2006: 10 Strangeness in p+p Large statistics data-set allows for the detailed analysis of data NLO calculations show good agreement with non-strange hadrons Agreement with strange hadrons is not as apparent, better for AKK than for Vogelsang Using Pythia (LO) requires changing the K factor to match the data EPOS has very good agreement with all particles, even Xi (See also talk by S Salur on Σ * )

SQM 2006: 11 gluon vs quark 200 GeV Λ/Λ ratio show dominance of gluon jets when compared to Pythia, but is not conclusive. m T scaling first studied using ISR data no absolute scaling observed in p+p, but applying pre-factors shows some universal behaviour for baryons and mesons

SQM 2006: 12 m T scaling in Pythia Pythia shows shape differences on the whole Gluon jet events show the difference Quark jet events show no difference Evidence for gluon jet domination at RHIC?

SQM 2006: 13 Baryons vs Mesons Oregon nucl-th/ The Λ/K 0 S ratio from Yr2 data exhibits a peak in the intermediate p T region which is consistent with ReCo models. The Λ/K 0 S ratio from Yr4 data extends this measurement to higher p T and shows that all centralities appear to converge again nucl- ex/

SQM 2006: 14 R CP : 200 and 62 GeV R CP from Yr2 show clear difference between baryons and mesons at intermediate p T The Φ and K* clearly follow the mesons and not the baryons, not a mass effect Data from Yr4 extend the measurement out to much higher p T The strange and non- strange baryons and mesons are consistent and appear to show a similar suppression for p T > 5 GeV/c. 62 GeV data also shows baryon-meson splitting Ratios go higher than at 200 GeV - Cronin? 200 GeV NA57 √s NN = 17.2 GeV 0-5% 40-55%

SQM 2006: 15 Rcp vs Energy STAR Preliminary NA57: G. Bruno, A. Dainese: nucl- ex/ The top SPS and top RHIC energy data are consistent 62 GeV Au+Au data also follows the same trend Is coalescence present in all systems? Will soon be able to test with Cu+Cu data at 200 and 62 GeV

SQM 2006: 16 Strange Correlations in Au+Au ΔΦ correlations per trigger particle 3 < p T trigger < 3.5 GeV/c 1 < p T assoc < 2 GeV/c |η| < 1 Correlations corrected for TPC acceptance and efficiency of associated particles Near side v 2 is then subtracted to give final correlations Λ-h K 0 S -h Λ-h K 0 S -h Λ-h

SQM 2006: 17 Correlations: near side yields STAR Preliminary No trigger particle dependence in the near side yield/trigger in either d+Au or Au+Au d+AuAu+Au STAR Preliminary No definite trigger particle dependence vs centrality but meson triggers appear to be systematically below baryon triggers Reason for increase may be due to longe range correlations in η Λ-h K 0 S -h h-h Λ-h K 0 S -h h-h Λ-h K 0 S -h h-h Λ-h K 0 S -h h-h Λ-h K 0 S -h h-h Λ-h

SQM 2006: 18 ReCo model and Correlations R. Hwa, Z. Tan: nucl- th/ The ratio of near side yields in central to peripheral collisions is around 3 at 1 GeV/c and decreases with increasing p T assoc This is in good qualitative agreement with ReCo model predictions though there are some differences to the model (trigger p T, centrality) Long range dη correlations are visible in the STAR data and not taken into account in the plot. This is p T dependent and may reduce any slope. 0-10%/40-80% 3 < p T trigger < 6 Λ,Λ-h K 0 S -h h-h

SQM 2006: 19 Recent ReCo Model Predictions Premise: Observables: 2) Any Ω or Φ di-hadron correlations are swamped by the background and not observed Being actively studied, but no results are available as yet STAR Preliminary The production of Φ and Ω particles is almost exclusively from thermal s quarks even out to 8 GeV/c 1)The ratio of Ω/Φ yields should rise linearly with p T

SQM 2006: 20 Correlations in Cu+Cu Strange particle correlations are observed at intermediate p T trigger Measurement is statistically challenging, but factor 10x more stats on disk !! 0-10%10-40%40-80% 2<p T Trig <3 1<p T Asso <2 4<p T Trig <1 0 1<p T Asso <2 STAR Preliminary

SQM 2006: 21 Summary and Conclusions Strangeness is proving to be a very interesting and versatile probe at RHIC !! Bulk MeasurementsAbove the Bulk Production smooth with energy Enhancement similar to SPS energies  Data provide a strict constraint on T chem v 2 measured to high p T  Baryon-meson splitting in the intermediate to high p T region Multi-strange particles flow just as well as other particles  partonic collectivity? Baryon-meson scaling observed High statistics p+p measurement  Provides a challenge to different models to reproduce the data  Comparisons to Pythia indicate dominance of gluon jets New high statistics Λ/K 0 S and R CP measurements  Baryons and mesons exhibit similar suppression for p T > 6 GeV/c  Double ratio independent of energy!! Identified di-hadron correlations at intermediate p T  No trigger particle dependence in the intermediate p T region  Consistent with ReCo model  Measurements possible in Cu+Cu Ω/Φ ratio not conclusive, but work is ongoing on this and Ω-h correlations

SQM 2006: 22

SQM 2006: 23 Δη correlations - the ridge