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Identified Particle Ratios at large p T in Au+Au collisions at s NN = 200 GeV

Identified Particle Ratios at large p T in Au+Au collisions at s NN = 200 GeV. Matthew A. C. Lamont for the STAR Collaboration. - Talk Outline - Physics Motivation Current Models Identified Particle Spectra B/B and B/M ratios Strange Particle Correlations.

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Identified Particle Ratios at large p T in Au+Au collisions at s NN = 200 GeV

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  1. Identified Particle Ratios at large pT in Au+Au collisions at sNN = 200 GeV Matthew A. C. Lamont for the STAR Collaboration - Talk Outline - Physics Motivation Current Models Identified Particle Spectra B/B and B/M ratios Strange Particle Correlations

  2. Motivation : Particle production vs pT What has the data already shown us at intermediate pT ? What do we think we know ? • pT independence of p/p ratio. • p/p ratio increases with pT to ~ 1 at pT ~ 3-4 GeV/c in central collisions. • Suppression factors of p, L different to that of p, K0s in the intermediate pT region. pQCD Hydro What are the mechanism(s) atintermediate pT? Fragmentation and quenching of jets Soft pT 0 2-3 GeV/c 6-7 GeV/c ? Matthew A. C. Lamont - QM2004

  3. Soft + Quench Model Two component model, soft production (hydro) at low pT, quenching of pQCD jets via gluon radiation at higher pT. Baryon junctions incorporated to explain large baryon yield at intermediate pT. Current theoretical models M. Gyulassy et. al., Phys. Rev. Lett. 86 (2001) 2537 • Recombination • Model assumes the recombination of two and three low pT partons to form hadrons from an exponential parton pT spectrum. High pT spectrum described by fragmentation once parton pT spectrum can be described by a power law. • Requires a high phase space density of partons for method to work. R. J. Fries et. al., Phys. Rev. C 68 (2003) 044902 • Coalescence • Same as the recombination picture with the added assumption that thermal ‘QGP’ partons can coalesce with co-moving ‘pQCD’ partons from a mini-jet. V. Greco et. al., Phys. Rev. C 68 (2003) 034904 Matthew A. C. Lamont - QM2004

  4. Identified particle spectra : p, p, K-,+, p-,+, K0s and L Matthew A. C. Lamont - QM2004

  5. B/B ratios vs Transverse Momentum (pT) This pQCD calculation fails : uncertainties in PDFs and fragmentation functions ? Both the ‘Soft+Quench’ and recombination model predictions are consistent with the data. Note the different trend in the p/p ratio from that reported in Nantes. Experimental effects have been better modelled (mainly space charge distortions). Soft+Quench (130 GeV) : Nucl. Phys. A715 779-782 (2003) Recombination (200 GeV) : Phys. Rev. C68 044902 (2003) Matthew A. C. Lamont - QM2004

  6. p/p- ratios, data and theory • S+Q : magnitude  low pT • Hydro : magnitude  low pT • Reco : magnitude  low pT • Coal : magnitude  low pT Note that p data is not corrected for feed-down from weak decays  p/p ratio will decrease. Reco : Phys. Rev. C68 044902 (2003) Coal : Phys. Rev. C68 034904 (2003) Hydro: Phys. Rev. C67, 044903 (2003) S+Q: 200 GeV data - private communication S+Q: 130 GeV data - Phys. Rev. C65, 041902 Matthew A. C. Lamont - QM2004

  7. L/K0s ratio increases with increasing centrality peaks in the intermediate pT region. turns over and appears to tend to the same value for all centralities for pT ~ 5-6 GeV/c. Therefore pT range of baryon excess is limited to < 5-6 GeV/c. Not yet down to level in pp data L/K0s ratios vs collision centrality For p+p data, refer to poster by M. Heinz and J. Adams L not corrected for feed-down from weak decays - estimated to be a 10% effect and ~ independent of pT. Matthew A. C. Lamont - QM2004

  8. L/K0s - comparison with models • S+Q : magnitude  turnover  centrality  • Reco : magnitude  turnover  low pT  • Coal : magnitude  turnover  low pT Require centrality dependent prediction from Recombination and Coalescence models. S+Q : 200 GeV data - private communication S+Q : 130 GeV data - Phys. Rev. C65, 041902 Reco : Phys. Rev. C68 044902 (2003) Coal : Phys. Rev. C68 034904 (2003) Matthew A. C. Lamont - QM2004

  9. Suppression of mesons different to baryons - not mass dependent effect. Rcp of baryons and mesons separate at pT ~ 2 GeV/c and come together at pT ~ 5-6 GeV/c. Another view of the same effect? …. Rcp See poster by P. Sorensen Matthew A. C. Lamont - QM2004

  10. We have seen previously the disappearance of back-to-back jet correlations in central Au+Au, with charged particles. Identified Particle Correlations trig: L, assoc : charged hadron 1/NTriggerdN/d() dashed line is random background Back to back jet disappearance for charged trigger particles (Phys. Rev. Lett. 91 072304 (2003)) • Measuring correlations with identified particles could give us insight on possible different production mechanisms for baryons and mesons. ∆(radians) (trigger pT > 2.5 GeV/, associated pT > 2.5 GeV/c & less than trigger pT) trig: L, assoc : charged hadron • Q) Can we measure particle correlations with identified particles ? • A) Yes - though measurements are limited by statistics. • Correlation appears stronger for L compared to L, though in both cases, there is an absence of a ‘back-to-back’ partner correlation. 1/NTriggerdN/d() Back side Back side Same Side See poster by Y. Guo ∆(radians) Matthew A. C. Lamont - QM2004

  11. Correlation difference defined as : Nsame - Nback trig: L, assoc : charged hadron Nsame - Nback trig: L, assoc : charged hadron Back side trig: L, assoc : charged hadron trig and assoc : charged hadron dash lines indicate estimated flow contribution Nsame - Nback trig: K0s, assoc : charged hadron Trigger PT Trigger PT Trigger PT Same side Trigger PT Quantifying the Correlation Strength • Suppression of  as a function of pT is slightly different from the , K0s and primaries. • Under investigation whether this is an experimental effect or whether there is indeed sensitivity to quenching or production mechanism effects See poster by Y. Guo Matthew A. C. Lamont - QM2004

  12. Summary • B/B ratios are independent of pT. • pQCD calculation fails : uncertainties in PDFs and fragmentation functions ? • p/p- ratio increases with pT up to 3 GeV/c. • L/K0s ratio increases smoothly with centrality, turns over at pT ~ 3 GeV/c. • baryon excess over mesons is limited in pT to < 5-6 GeV/c. • A+A value still above p+p value. • The Rcp measurement exhibits differences between baryons and mesons - not just a mass effect. • Strange correlations hint at a flavour dependence. • correlations with L triggers possibly enhanced over those with L and K0s triggers. Matthew A. C. Lamont - QM2004

  13. Backup Slides Matthew A. C. Lamont - QM2004

  14. Ratio very different in two systems Different production mechanisms or just differences in experiments ? STAR pp vs UA1 pp Matthew A. C. Lamont - QM2004

  15. ~235cm STAR RICH Geometry |h|<0.3 and Df = 20o • Charged particle through radiator • MIP and photons detection Matthew A. C. Lamont - QM2004

  16. pions kaons protons Integral method and Fitting Cherenkov angle distribution in momentum bins Matthew A. C. Lamont - QM2004

  17. Comparison of Spectra with PHENIX Matthew A. C. Lamont - QM2004

  18. Soft + Quench Model Two component model, soft production (hydro) at low pT, quenching of pQCD jets via gluon radiation at higher pT. Baryon junctions incorporated to explain large baryon yield at intermediate pT. Current theoretical models • Coalescence • Same as the recombination picture with the added assumption that thermal ‘QGP’ partons can coalesce with co-moving ‘pQCD’ partons from a mini-jet. • Recombination • Recombination of two and three low pT partons form hadrons from an exponential parton pT spectrum. High pT spectrum described by fragmentation due to power-law parton pT spectrum. • Requires a high phase space density of partons for method to work. V. Greco et. al., Phys. Rev. C 68 (2003) 034904 M. Gyulassy et. al., Phys. Rev. Lett. 86 (2001) 2537 R. J. Fries et. al., Phys. Rev. C 68 (2003) 044902 Matthew A. C. Lamont - QM2004

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