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What’s Missing in our Current Picture from High p T Measurements at RHIC?

What’s Missing in our Current Picture from High p T Measurements at RHIC?. Saskia Mioduszewski Texas A&M University. 23 March, 2007. Single-Particle Spectra – What have we learned?.

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What’s Missing in our Current Picture from High p T Measurements at RHIC?

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  1. What’s Missing in our Current Picture from High pT Measurements at RHIC? Saskia Mioduszewski Texas A&M University 23 March, 2007

  2. Single-Particle Spectra – What have we learned? High-pT suppression comparison to theory: GLV  dNg/dy ~ 1000 I. Vitev and M. Gyulassy, PRL 89 (2002) 252301  Initial energy density: e0 ~ 15 GeV/fm3 Hadrons are suppressed, photons are not – photons serve as the “control” experiment PHENIX, Phys. Rev. Lett. 96, 202301 (2006)

  3. PHENIX p0 Spectrum What can we learn about Energy Loss? Fractional effective energy loss: Sloss(MJT) “Effective” because of surface bias when analyzing single particle spectra PHENIX, nucl-ex/0611007 Renk and Eskola, hep-ph/0610059 8 < pT < 15 GeV/c

  4. New Understanding of Energy Loss through Heavy Flavor? GLV calculation requires collisional energy loss to describe electrons from heavy-flavor decays  perhaps collisional energy loss not negligible as previously assumed S. Wicks, QM 2006 STAR: nucl-ex/0607012, PHENIX (QM2006): nucl-ex/0611018

  5. Heavy flavor suppression– Challenge to Theory Electrons from heavy-flavor decays are more suppressed than expected, in particular with non-zero contribution from bottom X. Lin, QM 2006 p+p collisions

  6. Escaping Jet “Near Side” Lost Jet “Far Side” pedestal and flow subtracted Di-Jets through Hadron-Hadron Correlations “Disappearance of away-side jet” in central Au+Au collisions 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig 0-5% STAR, PRL 90 (2003) 082302 IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

  7. pedestal and flow subtracted Evolution of Jet Structure M. Horner, QM 2006 At higher trigger pT (6 < pT,trig < 10 GeV/c), away-side yield varies with pT,assoc 4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig For lower pT,assoc (1.3 < pT,assoc <1.8 GeV/c), away-side correlation has non-gaussian shape  becomes doubly-peaked for lower pT,trig

  8. STAR preliminary near Medium away mach cone near 0-12% 200 GeV Au+Au Medium away deflected jets Hard-soft correlations 4 < pT,trig< 6 GeV/c Hard-soft: away-side spectra approaching the bulk. Inclusive in top 5%? • Three-particle correlation – N.N. Ajitanand, J. Ulery STAR, PRL 95,152301 (2005)

  9. Au+Au 20-30% Near-side Correlation J. Putschke, QM 2006 Au+Au 0-10% STAR preliminary Additional long-range correlation in Dh the “ridge” Coupling of high pT partons to longitudinal expansion - Armesto et al, PRL 93 (2004) QCD magnetic fields- Majumder et al, hep-ph/0611035 In recombination framework: Coupling of shower partons to thermal partons undergoing longitudinal expansion- Chiu & Hwa Phys. Rev. C72:034903,2005 Radial flow + trigger bias – S.A. Voloshin, Nucl. Phys. A749, 287 (2005)

  10. J = near-side jet-like corrl. R = “ridge”-like corrl. 2 (J) ||<0.7 (J) ||<0.7 1 2 const bkg. subtracted const bkg. subtracted  (J+R) - (R) (J) flow (v2) corrected (J+R) ||<1.7 (J+R) ||<1.7 no bkg. subtraction v2 modulated bkg. subtracted Extracting near-side “jet-like” yields J. Putschke, QM 2006 Au+Au 20-30%

  11. “Jet” spectrum vs. “Ridge” spectrum J. Putschke, QM 2006 STAR preliminary STAR preliminary STAR preliminary “jet” slope “ridge” slope inclusive slope

  12. Ridge Yield J. Putschke, QM 2006 pt,assoc. > 2 GeV STAR preliminary Ridge yield persists up to highest trigger pT and approximately constant yield

  13. “Reappearance of away-side jet” With increasing trigger pT, away-side jet correlation reappears STAR, Phys. Rev. Lett. 97 (2006) 162301 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig

  14. Surface Bias of Di-Jets? STAR, Phys. Rev. Lett. 97 (2006) 162301 8 < pT,trig< 15 GeV/c Renk and Eskola, hep-ph/0610059 8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c

  15. Comparison of IAA to RAA D. Magestro, QM 2005 8 < pT(trig) < 15 GeV/c  = Near-side IAA  = Away-side IAA IAA = Yield(0-5% Au+Au) Yield(d+Au) In the di-jets where trigger pT is 8-15 GeV/c, the suppression is same as for single particles as a function of pT

  16. Near-side Yields vs. zT After subracting the Ridge M. Horner, QM 2006

  17. Away-side Yields vs. zT M. Horner, QM 2006

  18. Away-side suppression as a function of pT,trig Away-side suppression reaches a value of 0.2 for trigger pT > 4 GeV/c, similar to single-particle suppression M. Horner, QM 2006 Away-side IAA IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

  19. 4 < pT,trig< 6 GeV/c, 2 < pT,assoc< pT,trig Out-plane In-plane STAR STAR, Phys. Rev. Lett. 93 (2004) 252301 What other handles do we have? Centrality, trigger and associated pT,….. ….Reaction plane

  20. q g Another handle: g-jet Wang et al., Phys.Rev.Lett. 77 (1996) 231-234 Increasing ratio of direct photons to decay photons with centrality due to hadron suppression at high pT PHENIX, Phys. Rev. Lett. 94, 232301 (2005) Photon-jet measurement is, in principle, sensitive to full medium Bias to where away-side jet is close to surface? Together with di-jet measurement for comparison  Another differential observable

  21. q g 1/NtrigdN/dDf Df(rad) Another handle: g-jet Current Results from Run-4 Au+Au collisions: T. Dietel, QM 2005 J. Jin, QM 2006

  22. Summary • Limited information extracted from single-particle pT spectra • Effective fractional energy loss reaches 20% for most central collisions • Initial energy density ~ 15 GeV/fm3 from radiative energy loss models • Di-Jets (those that are observed) may have less surface bias • Photon-Jet Measurement will complement the di-jet for more complete probe • Heavy-flavor suppression not consistently described by theoretical models with light meson suppression – need elastic energy loss

  23. Conclusions What is missing from our picture? • Need a consistent theoretical approach to describe different observables • Need more quantitative model predictions for “ridge” explanation • Need more quantitative descriptions of jet modifications from experimenters • Particle species in ridge vs. in jet (J. Bielcikova’s talk) • Path-length dependence of jet-correlated yields (using reaction plane dependence) • Need a great deal of statistics for g-jet measurement (J. Dunlop’s talk)

  24. 3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV Jet+Ridge () Jet () Jet) STAR preliminary yield,) Npart

  25. Sloss • S(pT )/pT = S0, • is a constant for all pT > 3 GeV/c, which also results in a • constant ratio of the spectra, RAA(pT ). For the constant • fractional shift, the Jacobean is simply dS(pT )/dpT = S0 • RAA(pT ) = (1 + S0)−n+2 • RAA(pT )1/(n−2) =1/(1 + S0) • The effective fractional energy loss, Sloss, is related to • the fractional shift in the measured spectrum, S0. The • hadrons that would have been produced in the reference • p + p spectrum at transverse momentum pT + S(pT ) = • (1 + S0)pT , were detected with transverse momentum, • pT , implying a fractional energy loss: • Sloss = 1 − 1/(1 + S0) = 1 − RAA(pT )1/(n−2)

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