04/14/2010Workshop on Critical Examination of of RHIC Paradigms1 Review of particle spectrum data Outline: What have we learnt from published data bulk properties: low p T identified particle spectra jet quenching: nuclear modification factors at high p T recombination/coalescence: particle production at intermediate p T The recent results on blast-wave model using Tsallis-like distributions color charge and flavor dependence of energy loss constrain fragmentation functions at high p T Summary and outlook Strangeness enhancement – Rene’s talk Lijuan Ruan (Brookhaven National Laboratory)

04/14/2010Workshop on Critical Examination of of RHIC Paradigms2 Identify and study the properties of matter with partonic degrees of freedom (flavor, color, sound, temperature …) 1.Penetrating probes: parton energy loss in the medium identified particle spectra at high p T, heavy flavor and quarkonia jets … 2.Bulk properties: energy density, collectivity and freeze out properties identified particle spectra at low p T, v 2 … Physics Goals at RHIC S. Bass

04/14/2010Workshop on Critical Examination of of RHIC Paradigms3 PID Spectra – Freeze-out dynamics RHIC’s strength of measuring many particle species:  K(p); resonant and multi-strangeness states Chemical freeze-out: distribution of particle species Kinetic freeze-out: momentum spectra RHIC: Nucl. Phys. A 757 (2005)

04/14/2010Workshop on Critical Examination of of RHIC Paradigms4 Chemical Freeze-out  s approach 1 in central Au+Au collisions: thermalization within the framework of this model. Chemical freeze out temperature ~ 160 MeV, no centrality dependence in Au+Au, close to T critical ; baryon chemical potential  B ~20 MeV STAR: Nucl. Phys. A 757 (2005) 102

04/14/2010Workshop on Critical Examination of of RHIC Paradigms5 Kinetic freeze out properties 1. Kinetic freeze out temperature decreases from peripheral to central collisions 2.Velocity profile increases from peripheral to central collisions. 3.  and  have smaller cross sections at hadronic stage, freeze out earlier. STAR: Nucl. Phys. A 757 (2005) 102 Blast-wave model: E.Schnedermann et al, PRC48 (1993) whereand peripheralcentral

04/14/2010Workshop on Critical Examination of of RHIC Paradigms6 Probes between chemical and kinetic freeze out PRL97(2006) Phys. Lett. B 612 (2005) 181 Phys. Rev. Lett. 99 (2007) Phys. Rev. C 71 (2005) Phys. Rev. Lett. 92 (2004) Resonances: probe hadronic interactions via re-scattering of their daughter particles and regeneration Life time:  0 (1.3 fm)  ++ (1.6 fm) K* (3.9 fm)  (1385) (5.5 fm)  (1520) (12.6 fm)  (41 fm) …  (  p) >  (  ) >  (  K) Derive the life time of hadronic stage 3-10 fm/c

04/14/2010Workshop on Critical Examination of of RHIC Paradigms7 High p T : penetrating probe In central Au+Au collisions at RHIC: Fragmentation + energy loss at p T > 6 GeV/c: Significant suppression of inclusive charged hadron observed at p T >6 GeV/c: dN g /dy~1000. M. Gyulassy et al., nucl-th/ RHIC: Nucl. Phys. A 757 (2005) q q

04/14/2010Workshop on Critical Examination of of RHIC Paradigms8 Intermediate p T : baryon/meson pattern At p T ~2 GeV/c, pbar/  ratio ~1.  It can not be factorized jet fragmentation (D q/g (pbar)/D q/g (  ) << 1). At 2<p T <5 GeV/c, p,  increase faster than , K S, K from peripheral to central collisions. STAR: Phys. Rev. Lett. 92 (2004) ; PHENIX: Phys. Rev. Lett. 91 (2003) ; V. Greco, et al., Phys. Rev. Lett. 90, (2003).

04/14/2010Workshop on Critical Examination of of RHIC Paradigms9 hydro+jet: interplay between soft and hard N SOFT ~N HARD pTpTpTpT (1/p T )(dN/dp T ) Hydrodynamicafterburner Jetquenching Interesting region  Intermediate p T (2<p T <3.5 GeV/c) Pion  hard, Proton  soft T.Hirano & Y.Nara(’03), PRC69(2004) Crossing p T moves toward high p T soft hard Au+Au at b=2 fm P T, cross~ 1.8 GeV/c for  2.7 GeV/c for K 3.7 GeV/c for p T. Hirano, QM2004

04/14/2010Workshop on Critical Examination of of RHIC Paradigms10 Consequence from hadron species dependent p T,cross Hydro+Jet T.Hirano & Y.Nara(’03), PRC69(2004)034908

04/14/2010Workshop on Critical Examination of of RHIC Paradigms11 Recombination/Coalescence at hadronization Fragmentation works for p+p collisions for hadrons at p T > 2 GeV/c If phase space is filled with partons, recombine/coalesce them into hadrons. (hadrons at 2 < p T < 6 GeV/c) baryon enhancement, v 2 NCQ scaling. fragmenting parton: p h = z p, z<1 recombining partons: p 1 +p 2 =p h R.J. Fries, QM2004

04/14/2010Workshop on Critical Examination of of RHIC Paradigms12 Recombination/Coalescence models Recombination/Coalescence models predict that a scale according to the number of constituent quarks in a hadron seems to govern the particle production at intermediate p T. R.J. Fries et al., Phys. Rev. C 68, (2003). R. C. Hwa et al., Phys. Rev. C 70, (2004). V. Greco et al., Phys. Rev. Lett. 90, (2003).

04/14/2010Workshop on Critical Examination of of RHIC Paradigms13 Centrality Dependence: R CP in Au+Au 2<p T <6GeV/c, K*,  follow meson trend  coalescence + jet model works, however, errors on K*, , ,  are also big. Coalescence does not necessarily mean that baryon (meson) R CP are the same. STAR: Nucl. Phys. A 757 (2005) 102

04/14/2010Workshop on Critical Examination of of RHIC Paradigms14 From previous to now Bulk properties (energy density, collectivity and freeze out properties): p T <2 GeV/c Jet energy loss + fragmentation: high p T >6 GeV/c Coalescence/recombination: intermediate p T. The recent resents on: Freeze out properties: thermal-like replaced by Tsallis-like Constrain fragmentation function: light quark and gluon FFs Jet quenching: q,Q,g

04/14/2010Workshop on Critical Examination of of RHIC Paradigms15 Limitation of the Blast-wave Strong assumption on local thermal equilibrium Arbitrary choice of p T range of the spectra Flow velocity =0.2 in p+p Lack of non-extensive quantities to describe the evolution from p+p to central A+A collisions – in p+p collisions Levy function or m T power-law –in A+A collisions Boltzmann or m T exponential minbias STAR PRL99

04/14/2010Workshop on Critical Examination of of RHIC Paradigms16 Tsallis statistics in Blast-wave model BGBW: With Tsallis distribution: Tsallis Blast-wave (TBW) equation is:

04/14/2010Workshop on Critical Examination of of RHIC Paradigms17 Fit results in Au+Au collisions Zebo Tang,Yichun Xu, Lijuan Ruan, Gene van Buren, Fuqiang Wang and Zhangbu Xu, Phys. Rev. C 79, (R) (2009)

04/14/2010Workshop on Critical Examination of of RHIC Paradigms18 Fit strange hadrons only Strangeness, Au+Au 0-10%: = T = q = chi^2/nDof = 51/99 T strange >T light-hadrons Strangness decouple from the system earlier All available species M. Shao, L. Yi, Z. Tang, H. Chen, C. Li and Z. Xu, arXiv:

04/14/2010Workshop on Critical Examination of of RHIC Paradigms19 Centrality dependence for T and <    Multi-strange hadrons decouple earlier Hadron rescattering at hadronic phase doesn’t produce a collective radial flow, instead, it drives the system off equilibrium Partons achieve thermal equilibrium in central collisions M. Shao, L. Yi, Z. Tang, H. Chen, C. Li and Z. Xu, arXiv: strange non-strange

04/14/2010Workshop on Critical Examination of of RHIC Paradigms20 Flavor and color charge dependence of energy loss STAR: PRL98(2007) STAR: PRL97,152301(2006) Bottom energy loss, significantly as light flavor: no mass effect on partonic energy loss? heavy quark spectra steeper than calculated in the FONLL calculations? Collisional dissociation of heavy mesons, in-medium heavy resonance diffusion, multi-body mechanisms might play an important role for heavy quark energy loss A. Adil and I. Vitev, Phys. Lett. B649, 139 (2007); H. van Hess, V. Greco and R. Rapp, Phys. Rev. C 73; (2006); W. Liu and C. M. Ko, nucl-th/ Common suppression of protons and pions: no color charge dependence of partonic energy loss?

04/14/2010Workshop on Critical Examination of of RHIC Paradigms21 Quark Discussion: g/q jets conversion in the medium gluon/quark jets conversion in the medium. (W. Liu et al., nucl- th/ ; C.M. Ko, ISMD2006.) elastic scattering: q g g q, qbar g g qbar. inelastic scattering: q qbar g g There is net quark to gluon jets conversion in the medium. A much larger net conversion is needed to explain the data. gluon At RHIC, initially produced hard strange quarks are much fewer than the strange quarks in a hot, dense medium. The interaction between the initially produced light quark (gluon) and the medium will lead to more strangeness production at high p T Using the same factors, Liu and Rries predicts R AA (K S 0 ) > R AA (  ) This leads to jet hadron chemistry change in AuAu collisions compare to in pp collisions. W. Liu and R. Fries, PRC77(2008)054902

04/14/2010Workshop on Critical Examination of of RHIC Paradigms22 Jet hadro-chemistry in Au+Au and p+p The final jet hadro-chemistry change was observed: K/  (Au+Au) > K/  (p+p); R AA (p+pbar, K) > R AA (  ) ~ R AA (  ) Consistent with jet conversion mechanisms and/or modified enhanced parton splitting in the hot, dense medium S. Sapeta and U.A. Wiedemann, arXiv: How significant the effect is? STAR Preliminary Yichun Xu, QM2009

04/14/2010Workshop on Critical Examination of of RHIC Paradigms23 Sample of R AA in PHENIX C. Vale QM2009

04/14/2010Workshop on Critical Examination of of RHIC Paradigms24 Constrain Fragmentation Functions: kaon in 200 GeV p+p at high p T Spectra in p+p collisions at p T >2 GeV/c: convolution of PDF  pQCD  FF Charged and neutral kaons are extended up to 15 GeV/c in p+p collisions. Charged and neutral kaons are consistent; provide constraints on FFs. Low p T K S : STAR Phys. Rev. C 75 (2007) STAR preliminary Yichun Xu, QM2009

04/14/2010Workshop on Critical Examination of of RHIC Paradigms25 Constrain fragmentation function In 200 GeV p+p collisions  - /  +, pbar/p decrease versus p T indicating valence quark effect plays a significant role at high p T in particle production PYTHIA can describe the ratios better but deviates from the spectra data. NLO calculations describe spectra better but deviate from ratio STAR preliminary This is important to understand gluon/quark contribution factors to proton, pion and kaon Yichun Xu, QM2009

04/14/2010Workshop on Critical Examination of of RHIC Paradigms26 Energy dependence of particle composition Phys. Lett. B 655 (2007) 104, Phys. Rev. Lett. 97 (2006) In 62 and 200 GeV Au+Au collisions: 1.Λ/K S ratio: similar peak positions. 2.p(pbar)/  ratios: similar shapes at p T >2 GeV/c. STAR preliminary

04/14/2010Workshop on Critical Examination of of RHIC Paradigms27 Constrain intermediate p T model calculations There are quantitative differences between data and current models at intermediate p T. Hard component should be able to help constrain the reco/coalescence model calculations. STAR preliminary, QM2006

04/14/2010Workshop on Critical Examination of of RHIC Paradigms28 Summary The identified particle spectra measurements is consistent with the picture of a hot dense medium created at RHIC. The recent measurements call for: Understand particle production mechanisms in p+p, constrain fragmentation functions. Understanding of jet quenching in detail. Improved intermediate p T calculations by coalescence/recombination models. Thanks!!