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Production and Flow of Identified Hadrons at RHIC

Production and Flow of Identified Hadrons at RHIC. Julia Velkovska. XXXIV International Symposium on Multiparticle Dynamics Sonoma State University, 2004. RHIC Specifications. 3.83 km circumference Two independent rings 120 bunches/ring 106 ns crossing time

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Production and Flow of Identified Hadrons at RHIC

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  1. Production and Flow of Identified Hadrons at RHIC Julia Velkovska XXXIV International Symposium on Multiparticle Dynamics Sonoma State University, 2004

  2. RHIC Specifications • 3.83 km circumference • Two independent rings • 120 bunches/ring • 106 ns crossing time • Capable of colliding ~any nuclear species on ~any other species • Energy: • 500 GeV for p-p • 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1 J.Velkovska

  3. Summary of RHIC runs so far • p+p : 200 GeV , baseline measurement • d+Au : 200 GeV , study cold nuclear matter • Au+Au : 200 GeV, Run2, Run4 : 130 GeV , Run1 : 62.4 GeV ( match top ISR energy) Run4 : very short 56 GeV, 19 GeV • Data in this talk: • mostly from 200 GeV runs • Mostly from PHENIX J.Velkovska

  4. 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Particle production at RHIC energies Bulk of particle production Collective phenomena Soft (hydro) pQCD ? New physics Hard probes Modified by the medium Jet Quenching This talk is focused at intermediate pT, but to get there we need to review both soft and hard particle production. J.Velkovska

  5. pp and dAu identified hadron spectra: mT scaling Idenpendent of mass, strangeness,etc - approximately same mT slope J.Velkovska

  6. Au+Au collisions • Modifications to soft processes from the nuclear medium • Slopes depend on particle mass • Spectra are NOT exponential in mT • Teffdepends on fitting range • Best to compare to full hydro calculations • Very low mT data from PHOBOS – constrain the amount of flow needed to describe the data J.Velkovska

  7. Example of Blast wave fits 0-10% central Au+Au 200 GeV Fit |mT –m0| < 1GeV Extrapolate F meson described by same Tfo , bT J.Velkovska

  8. Soft processes: Summary • mT “scaling” in pp and dAu collisions • Radial flow in AuAu collisions. Protons and anti-protons spectra significantly affected due to their large mass J.Velkovska

  9. Hard probes

  10. Why study hard scattering ? (in Brief) A main goal of relativistic heavy ion physics is to investigate high-temperature, high-density QCD, by creating and then studying the highly-excited medium produced in high-energy nuclear collisions. The full pallet of QCD probes can be created and measured in the RHIC experiments q: fast color triplet QCD probe out Induced gluon radiation? QCD probe in g: fast color octet Modification? Q: slow color triplet Excited medium (possible quark-gluon plasma?) Energy Loss? QQbar: slow color singlet/octet One method of diagnosing a QCD medium is to shoot a QCD-sensitive probe through it, then look for any modifications due to the medium. (Most obvious possibilities: multiple scatterings, induced radiations, and energy loss.) Dissociation? Virtual photon: colorless Controls Real photon: colorless Unknown Medium J.Velkovska

  11. p0 production in p+p • Good agreement with NLO pQCD • Factorization theorem: 200 GeV - Run2 AB hXfa/A(xa,Q2a)fb/B(xb,Q2b) a b cdDh/c(zc,Q2c) data vs pQCD KKP Kretzer • Constrains Fragmentation Function D(Gluon-pi) • Reference for Au+Au spectra J.Velkovska Phys. Rev. Let 91, 241803 (2003)

  12. Nuclear Modification Factor RAA/RCP Quantify deviations from expected behaviour in p+p collisions: <Nbinary>/inelp+p (Nuclear Geometry) • If no “effects”: • R < 1 in regime of soft physics • R = 1 at high-pT where hard scattering dominates  A+B = A*B(p+p) J.Velkovska

  13. strong suppression Nuclear Modification factor RAA for p0 @ 200 GeV Phys. Rev. Lett. 91, 072301 (2003) No modification for Peripheral AuAu Jet quenching due to the dense medium J.Velkovska

  14. RAA for p0 in Central Collisions: Energy Dependence Central AA Cronin enhancement at 17 GeV Suppression at 62 And 200 GeV Differences < 6 GeV/c A.L.S.Angelis, PLB 185, 213 (1987) WA98, EPJ C 23, 225 (2002) ,[ Renormalization: D.d'E. nucl-ex/0403055] PHENIX, PRL 88 022301 (2002) ; PHENIX, PRL 91, 072303 (2003) J.Velkovska

  15. Protons are not produced from colorless objects: but Ncollscaling ! J.Velkovska

  16. Large!!! baryon/meson ratios Phys. Rev. Lett 91, 172301(2003). Peripheral: consistent with standard fragmentation Central: a factor ~ 3 higher than peripheral, e+e- and ISR pp data p and pbar at pT 2-5 GeV/c : SOFT OR HARD ? J.Velkovska

  17. Scaling properties of (1020) proton, pbar: PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004) : PHENIX final data, will be submitted to PRC. •  meson: • Similar mass as proton, but meson. •  Ideal test particle whether the observed baryon anomaly is a mass effect or not. p, pbar: low pT (< 1.5 GeV/c): different shape due to the radial flow, intermediate pT: Ncoll scaling : does not scale with Ncoll J.Velkovska

  18. Rcp of p,p, • F mesons are heavy, but follow 0, not p+pbar! • Indicates the absence of suppression of proton at intermediate pT is not a mass effect. J.Velkovska

  19. Compilation on Rcp from STAR Presented by M. Lamont (QM04) baryon meson • Two distinct groups in Rcp , i.e. meson and baryon, not by particle mass. • Separate at pT ~ 2 GeV/c and come together at 5 GeV/c. J.Velkovska

  20. y y x x Azimuthal Anisotropy of Particle Emission low pThigh pT Bulk (Hydrodynamic) Matter Jet Propagation Pressure gradient converts position space anisotropy to momentum space anisotropy. Energy loss results anisotropy based on location of hard scattering in collision volume. J.Velkovska

  21. Elliptic Flow of baryons and mesons At low pT hydro works remarkably well Above ~ 2 GeV/c : A split between mesons and baryons v2 – too large to be attributed to jet absorption (geometric limit for surface emission exceeded) J.Velkovska

  22. Universal behavior in flow per quark J.Velkovska

  23. Recombination of quarks to explain the data Rcp p/ Duke model, PRC 68, 044902 (2003) describe Rcpparticle ratios , spectra, v2: pT(baryons) >pT(mesons)>pT(quarks) J.Velkovska

  24. jet partner equally likely for trigger baryons & mesons • flat centrality dependence (within errors) • expected from • purely thermal recombination • (nucl-th/0306027) Jet correlations with identified mesons and baryons A. Sickles Need partons from jets to explain the data!! J.Velkovska

  25. Jet correlations with identified particles: Star “jettiness” of intermediate pT baryons confirmed! J.Velkovska

  26. Summary • Au+Au collisions at RHIC form a bulk medium which exhibits collective effects • Radial flow (mass dependent) • Elliptic flow: descirbed by hydro at low pT , partonic description works at high pT • Hard probes: • Dense nuclear medium is responsible for jet quenching • dAu collisions show it is a final state effect • At intermediate pT baryons are not suppressed • Is there a new production mechanism at pT =2-5 GeV ? • Recombination: success and challenges • Hadron yields and elliptic flow scale with the number of quarks: Points to partonic degrees of freedom • baryons show jettiness – recombination of shower partons is needed J.Velkovska

  27. EXTRA J.Velkovska

  28. New data: RAA @ 62.4 GeV: Charged hadron and 0 0-10% • Common reference p+pcharged+X is used, instead of ISR 0 reference. • 0 yield is divided by (charged reference)/1.6. • Clear difference between charged and 0 at intermediate pT up to 4 GeV/c. • Suggests a large proton contribution in this pT region, as seen in 200 GeV data. charged 0 J.Velkovska

  29. Cronin effect stronger for protons than for pions • Not enough to account for factor of 3 increase of p/p in central AuAu J.Velkovska

  30. The proton “bump” in the h/p ratios Au+Au @ 200AGeV Expectation (pp, e+e-): h/p 1.6 Above 5 GeV/c and in peripheral collisions: recover standard fragmentation nucl-ex/0310005 J.Velkovska

  31. But what about the Cronin effect ? • Can Cronin effect produce the enhanced p/p ratio in AuAu ? • Usual description: “Initial state multiple scattering leading to pt broadening.” • Why is it different for protons and pions ? P.B. Straub et al., PRL 68 (1992) FNAL experiments measuring R (W / Be) for identified particles at sqrt(s) of 27.4 and 51.3 GeV. J.Velkovska P.B.Straub et al., Phys.Rev.Lett., 68,452(1992)

  32. PHENIX Preliminary PbGl / PbSc Combined 1 + (g pQCD direct x Ncoll) / gphenix backgrd Vogelsang NLO [w/ the real, suppressed background] 1 + (g pQCD direct x Ncoll) / (gphenix pp backgrd x Ncoll) AuAu 200 GeV Central 0-10% Direct photons: a colorless probe Built-in control experiment in the AuAu data. Direct photons are described by a curve that includes the measured suppressed p0production in AuAu. J.Velkovska

  33. Strange baryon/meson ratios • The mid-pT anomaly not unique to p/p: also seen for strange particles • With a little higher pT reach: L/K0shas a peak at ~ 3GeV/c • Height depends on centrality • Peripheral – above pp data J.Velkovska

  34. RAA for p0 and charged hadron PHENIX AuAu 200 GeV p0 data: PRL 91 072301 (2003), nucl-ex/0304022. charged hadron (preliminary) : NPA715, 769c (2003). J.Velkovska

  35. p/p in dAu, pp and AuAu HUGE nuclear effect Coming from the final state (hot nuclear matter) J.Velkovska

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