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Understanding Low-pT Phenomena at RHIC with Probes

Investigating bulk properties & particle correlations at extreme energy levels. Exploring QGP features using various probes in collisions. Analyzing hadron ratios, anisotropy, and expansion effects.

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Understanding Low-pT Phenomena at RHIC with Probes

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  1. Low pT領域のプローブによって何が分かったか?-- What we learned from low pT phenomena at RHIC? -- KANETA, Masashi 金田雅司 理研-BNL 研究センター RIKEN-BNL Research Center Masashi Kaneta, RBRC

  2. QGP Search Quark-Gluon Plasma A new state of matter under high pressure and/or temperature Existence predicted by QCD In early universe, neutron star, and relativistic heavy ion collisions • Relativistic Heavy ion experiments • Started from 1970’s • Bevalac (LBNL), SIS(GSI), AGS(BNL), SPS(CERN) • Now we have Relativistic Heavy Icon Collider (RHIC) at BNL Masashi Kaneta, RBRC

  3. Relativistic Heavy Ion Collider • 3.83 km circumference, 2 rings of super conducting magnet • Maximum 100 GeV of Au/250 GeV of p beam, and 100GeV d beam • 4 experiments PHENIX/STAR/PHOBOS/BRAHMS PHENIX event BRAHMS PHOBOS PHENIX STAR STAR event Masashi Kaneta, RBRC

  4. Physics in QGP and Its Probes • Parton phase deconfined • A phase transition to a QGP • Chiral phase transition • The properties of the chiral/QGP phase • Of cause, we should confirm QGP at first by probes • Photon • thermal radiation of hot has/QGP • Lepton • di-lepton : chiral transition, Debye screening by QGP • charm decay : charm enhancement • Hadron • dynamics of the system • temperature, flow (expansion effect), baryon stopping • strangeness enhancement • Isospin fluctuation Masashi Kaneta, RBRC

  5. Focus of This Talk pT spectra hadron ratios event anisotropy • Low pT phenomena • Study of bulk property from matter under extremely high energy and particle density • Particle abundance • Expansion effect from hadronic/partonic phase • Correlation of particles at final interaction Cartoon of space/time expansion time Hadron dominant elastic interaction dominant inelastic interaction dominant Parton dominant space Key: Locally thermal equilibrated expanding system Masashi Kaneta, RBRC

  6. Summary of SPS Energy time Thermal Freeze-out Chemical Freeze-out elastic interaction inelastic interaction space • CERN reported on 2000/Feb/10 • “A New State of Matter Created at CERN” • Results from A+A collisions at sNN~20GeV • High energy density (=3~4GeV/fm3, T~240MeV) • J/ suppression • Strangeness enhancement comparing p+p and p+A collisions • Expansion of the fireball • At  = 1 GeV/fm3 (T=170~180MeV), chemical freeze-out • the final abundances of the different types of particles are fixed • At  = 50 MeV/fm3 (T=100-120 MeV ), thermal freeze-out • the hadrons stop interacting completely and the fireball freezes out • Do we have a smoking gun? • Low pT phenomena (soft hadron process) is established in heavy ion collisions • But we want to have clear signal of thermalization,and hard probes (Jet quenching, charm excepting J/, bottom) Masashi Kaneta, RBRC

  7. Event Anisotropy Almond shape overlap region in coordinate space Momentum space z y x • The pressure gradient generates collective motion (aka flow) • Central collisions • radial flow • Peripheral collisions • radial flow and anisotropic flow In Perfect Hydrodynamical source, v2 is proportional to e Masashi Kaneta, RBRC

  8. Charged hadron v2 vs. Centrality central collision STAR : PRL86(2001)402, PRC66(2002)034904 130 GeV Au+Au hydrodynamical limit beam (collision) axis PHOBOS : PRL89(2002)222301 130 GeV Au+Au peripheral collision peripheral central peripheral central • 130GeV Au+Au collision data • v2: elliptically • Central collision region • Consistent with partonic hydrodynamical source picture • Reflected early stage geometry Masashi Kaneta, RBRC

  9. Energy dependence of v2 maximum <v2> RQMD: An event generator which includes only hadronic elastic/inelastic interaction RQMD(v2.4) • Increasing as a function of collision energy • Large v2 in RHIC energy Masashi Kaneta, RBRC

  10. Identified hadron v2 vs. pT STAR: PRL87(2001)182301 STAR: PRL89(2002)132301 130 GeV Au+Au 130 GeV Au+Au • Charged hadron seems to be consistent with hydrodynamical picture • OK. How about identified hadrons? • Hydrodynamical model can describe particle mass dependence Masashi Kaneta, RBRC

  11. Identified hadron v2 vs. pT STAR: nucl-ex/0306007 200 GeV Au+Au central peripheral central collision beam (collision) axis New result from PHENIX p0 v2 pT =1 to 10 GeV/c! Go to 11aSF on Sep.11 hydrodynamical model calc. central peripheral PHENIX: nucl-ex/0305013 phenix preliminary peripheral collision 200 GeV Au+Au 200 GeV Au+Au pT [GeV/c] • pT<2GeV/c region show agreement with hydrodynamical model • What happen in high pT? Let’s wait next talk! detail of v2 analysis １１aSF 江角晋一 Masashi Kaneta, RBRC

  12. Statistical Model View of Particle Ratios 130GeV ms=0 200GeV • Similar approach (canonical ensemble) works for p+p(p), e++e- collisions! [F.Becattini, EPJ C5(1998)143] ms0 • Full/partial Strangeness equilibration • A+A at SIS to SPS, LEP, SppS • gs~0.5-0.7 • Only RHIC • gs~1 • Application of thermo-chemical model to multi hadron system • J. Rafelski, Phys. Lett. B190 (1987) 167 • The particle ratios will be described by macroscopic parameters • Ideal Hadron gas (grand canonical ensemble) • Tch, mB, ms • and gs • dilution factor for full strangeness equilibration Lattice QCD predictions central collisions SPS Baryon Chemical Potential mB [GeV] parton-hadron phase boundary Neutron star <E>/<N>~1GeV, J.Cleymans and K.Redlich, PRC60 (1999) 054908 From M.K.’s talk in the first joint meeting of JPS and DNP, Hawaii, 2001 + SQM2003 Masashi Kaneta, RBRC

  13. Full Strangeness Equilibration peripheral central 130 GeV 200 GeV M.K.’s poster for international conference Strangeness in Quark Matter 2003 mB/3 • Approaching fully strangeness equilibration in central collisions in Au+Au collisions at RHIC • gs is 0.8 to 1.0 from peripheral to central collisions at RHIC • It is about 0.7 at AGS and SPS energy and p+p (SppS) e++e- (LEP) collisions • Centrality dependence at RHIC in 130 GeV Au+Au (and 200 GeV Au+Au central collision) • Strange quark potential msis close to zero • Close to phase boundary • Relation of ms and phase boundary is discussed in PRD51 (1995) 1086 and PRC53 (1996) 1353 Masashi Kaneta, RBRC

  14. How it works? M.K.’s poster for international conference Strangeness in Quark Matter 2003 • The statistical model can describe many particle ratios by only four parameters (Tch, mB, ms and gs)! Masashi Kaneta, RBRC

  15. Identified Hadron pT Distributions PHENIX: nucl-ex/0307010 STAR nucl-ex/0206008 PHENIX: PRL89 (2002) 092302 K0s p+ K+ K- p- L STAR: PRC65 (2002) 041901(R) p K+ K- L L p f p p p STAR PRC66 (2002) 061901(R) PHENIX: nucl-ex/0304022 STAR: nucl-ex/0307024 STAR: nucl-ex/0306029 X- p0 K*0 STAR: PRL89 (2002) 092301 p L X+ W-+W+ • A common view of pT distributions for identified hadrons •  Radial flow, so called Blast-wave model Those are 130 GeV Au+Au data we have same and more results for particle species of 200 GeV Au+Au Masashi Kaneta, RBRC

  16. pT Distributions (pT<2GeV/c) Blast wave model E. Schnedermann et al., PRC48 (1993) 2462 Boosted No Boost s • It is established from Bevalac to SPS results that • The pT distributions in heavy ion collisions are not simple superimpose of p+p collisions • Mass dependence • Large collision system has stronger dependence • Locally thermal equilibrated expanding source NA44 : PRL78 (1997) 2080 Masashi Kaneta, RBRC

  17. Radial Flow Effect PHENIX: PRL88 (2002) 242301 130 GeV Au+Au Only stat. errors are shown p p K- K- p- p- From QM2001 talk • 130 GeV Au+Au data shows • Inverse slope parameter/<pT> • mass dependence • increasing as a function of centrality (Npart) • 200 GeV data shows same tendency Masashi Kaneta, RBRC

  18. T and flow vs. Centrality K0 s ] 2 - GeV/c) [( T dp n dy 2 d T p p 2 ] 2 - GeV/c) [( T dp n dy 2 d T p p 2 200 GeV Au+Au 130 GeV Au+Au Blastwave model fit for STAR data From QM2002, M.K.’s poster p- K- K+ Data : O. Barannikova/F. Wang QM2002 Talk STAR preliminary Centrality 0-5% 5-10% 10-20% 20-30% 30-40% 40-50% 50-60% 60-70% 70-80% pT [GeV/c] Blastwave model fit for STAR data From QM2002, M.K.’s poster STAR: nucl-ex/0306029 pT [GeV/c] Masashi Kaneta, RBRC

  19. Collision Energy Dependence <r> [c] Tth [GeV] • Thermal freeze-out temperature seems to be saturate • Flow velocity looks still increasing PHENIX STAR Masashi Kaneta, RBRC

  20. All hadrons have same flow effect? STAR: nucl-ex/0307024 WA97: EPJ C14 (2000) 633 Inverse slope parameter T [GeV] line: E.Schnedermann et al. model • Strangeness show deviation from common flow and temperature from p/K/p T=Tfo + m<b>2 • Same behavior at RHIC Masashi Kaneta, RBRC

  21. Summary • Thermodynamical and statistical models are established by SPS energy and work at RHIC well • Event Anisotropy analysis suggest us the system reached early thermalization after heavy ion collisions • Full strangeness equilibration only central Au+Au collision at RHIC (particle ratio) • Hadronic or partonic flow? • Data show large flow in event anisotropy and pT distribution • It may have both hadronic (later stage) and partonic (early stage) effect. • The other topics in low pT physics • Bose-Einstein Correlation (11aSF 榎園昭智) • Event-by-event fluctuation (11aSF 中村智昭) Masashi Kaneta, RBRC

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