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K/ π Ratios as Hard Probe in RHIC/LHC

K/ π Ratios as Hard Probe in RHIC/LHC. 张一 上海师范大学物理系. Outline. “Little Bang”: RHIC Establishment RHIC – The most recent results The phase diagram of QCD Hard Probes in RHIC: Basics of perturbative QCD (pQCD) Hard particle productions in p-p, p-A and A-A collisions

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K/ π Ratios as Hard Probe in RHIC/LHC

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  1. K/πRatios as Hard Probe in RHIC/LHC 张一 上海师范大学物理系

  2. Outline • “Little Bang”: RHIC Establishment RHIC – The most recent results The phase diagram of QCD • Hard Probes in RHIC: Basics ofperturbative QCD (pQCD) Hard particle productions in p-p, p-A and A-A collisions K/πratios as hard probe in RHIC (LHC) • Conclusions/Outlook

  3. Big Bang Chiral symmetry breaking Quark-Gluon Plasma T(MeV) LHC Quark pairing 300 RHIC CERN-SPS Chandra X-ray SPS 200 100 Hadron Gas Color Superconductor 0 μ(MeV) 400 0 200 600 E. Shuryak, et. al. Phys.Rev.Lett. 81 (1998) T. D. Lee, C.G.Wick, Phys.Rev.D 9 (1974)

  4. The Relativistic Heavy Ion Collider

  5. RHIC 5-YEAR RUNNING

  6. Di-hadron Correlations Trigger on high pT and measure the associated hadron Fragments at time scales J.Adams et al., Phys.Rev.Lett.91 (2003)

  7. The Ridge from RHIC Jet Ridge Bulk Medium STAR: Joern Putschke, J.Phys.G34: S679 (2007) Rich underlying physics: jets, bulk, jet-medium interaction, medium responses,…

  8. pT and Centrality:π0 Spectra in Au+Au @ sNN = 200 GeV • π0 RAA now measured up to pT = 20 GeV/c (central Au+Au) • Constant RAA 0.2 in central Au+Au up to highest pT (5 < pT < 20 GeV/c) PHENIX, arXiv:0801.4020 [nucl-ex]

  9. pT and Centrality:π0 Spectra in Cu+Cu @ sNN = 200 GeV Cu+Cu, 200 GeV, 60-94% p0 PHENIX, arXiv:0801.4555 [nucl-ex] Cu+Cu, 200 GeV, 0-10% p0 RAA 0.6 – 0.7 in central Cu+Cu collisions at 200 GeV

  10. Hard Probes: Introduction Hard probes(of the medium created in RHIC): those whose benchmark (result of the probe in cold nuclear matter) can be studied using pQCD, for which a hard scale is required(p_T, Q,...>>1/Rh). QGP? QCD Probes in QCD Probes Out Strategy: results with no medium (pp) and cold nuclear matter effects (pA) understood in pQCD define the benchmark for the probe; results in hot medium (AB) and their difference with defined expectation provides a (perturbative or non-perturbative) characterization of the medium

  11. QCD: Factorizationin Hard Processes • Asymptotic freedom allows the use of pQCD for processes with a large • scale (m, transverse momentum,...) involving the QCD q, g fields. • For inclusive processes, factorization (Collins, Soper, Sterman, '85) is • the tool which makes it possible to use pQCD for hadronic processes.

  12. QCD: Factorization in Hard Processes Remarks: • Hard scattering elements computable in perturbation theory @ fixed order (LO or NLO), collinear, e.g., • f: PDF, flux of 'initial' partons in the hadron or nucleus (evolution with scale computable in perturbation theory) • D: FF, projection of 'final' partons onto the observed particle (evolution with scale computable in perturbation theory)

  13. pQCD: pp Collision PDF FF

  14. pQCD: pp Collision • Interactions among initial partons  Intrinsic k_T • Can be measured experimentally

  15. pQCD: Feynman-Field Fragmentation Function FF parameterizations, (1) BKK(2) KKP(3) Kretzer (4) AKK

  16. pQCD: pp Collision RHIC Energies

  17. New Parameterization for K? Feynman-Field FFs:When z  1, D[u-K]/D[u-π]  1-β/βwhere βsome constant New Kaon FFs (“Z”) based on KKP’s FF (“KKP”):When z  1, D[u-K]/D[u-π]  ½“K” = Kretzer’s FFs S.Kretzer, PRD. 62, 054001 (2002)

  18. K/π Ratios in pp Collisions K+/π+ scaling?Y. Zhang, unpublished (2005)More high p_T kaon data needed…

  19. p-A Collisions: Cronin Effect • pQCD (LO) for pp +Cronin + Shadowing • Cronin effect: nuclear multi-scattering increased particle production in 3 GeV < pT < 6 GeV range where ”increased” means more particles are produced in pA than expected from scaled pp collisions

  20. p-A Collisions: Shadowing Different shadowing parameterizations: (1) HIJ [S.-Y. Li and X.-N. Wang, PLB527(2002) 85-91](2) EKS[K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys.J., C9 (1999) 61](3) nPDF [M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905] (4) nDS[D. de Florian, R. Sassot, PRD69, (2004) 074028]

  21. p-A Collisions: Geometry

  22. p-A: Geometry cont’d

  23. A-A Collisions: Jet Tomography Jet Tomography: jet production and propagation in AA collision (inside hot dense matter) induced gluon radiation in a modified pQCD description

  24. A-A Collisions: Jet Tomography

  25. A-A Collisions: Jet Tomography Energy loss of jets decreases the momenta of parton c before its fragmentation: pQCD calculation for A-A collisions: geometrical overlap + shadowing + multi-scattering + jet-quenching + ... Nuclear modification factor:

  26. Jet Tomography Predictions I.Vitev., M.Gyulassy, Phys.Rev.Lett. 89 (2002)

  27. A-A Collisions: Jet Tomography STAR PHENIX

  28. K/πRatios in dA and AA Collisions • AuAu: HIJING shadowing, no jet Quenching! • is it sensitive to shadowing parameterization? • do we expect this from recombination mechanism? • jet quenching…LHC energies…NLO…? Y. Zhang and G. Fai, in preparation, (2008)

  29. Breakdown of (indep.) (pert.)Fragmentation U.A.Wiedmann, QM’04

  30. Fragmentation vs. Recombination Open Q: violates entropy conservation? U.A.Wiedmann, QM’04

  31. Conclusions • pQCD parton model + jet quenching - Provide powerful tools for RHIC data - Suggests energy density at RHIC more than 100 times cold nuclear matter density • K/π ratios displays some “scaling” property • K/π ratios might be sensitive hard probe in RHIC and LHC (in progress)

  32. High p_T Spectra @ RHIC

  33. 200 GeV p+p Gluons vs Quarks • q jets or g jets gluon jet contribution to protons is significantly larger than to pions at high pT in p+p collisions at RHIC; pbar/ < 0.1 from quark jet fragmentation at low beam energy .STAR Collaboration, PLB 637, 161 (2006). • From Kretzer fragmentation function, the g/q jet contribution is similar to AKK. S. Kretzer, PRD 62, 054001 (2000).

  34. Jet Tomography in Au-Au @ PHENIX

  35. Dh-Df Two-Component Ansatz     3<pt,trigger<4 GeV pt,assoc.>2 GeV • Study near-side yields • Study away-side correlated yields and shapes • Components • near-side jet peak • near-side ridge • v2 modulated background Au+Au 0-10% preliminary Strategy:Subtract  from  projection: isolate ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge()  Jet() Can also subtract large .

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