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Characteristics of p T  (N ch ) in Relativistic Heavy Ion Collisions

Characteristics of p T  (N ch ) in Relativistic Heavy Ion Collisions. Thomas S. Ullrich Brookhaven Nation Laboratory and Yale University February 9, 2003. Modeling Initial Conditions Hard and Soft in Elementary Collisions STAR Results … … and how they Compare to Models.

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Characteristics of p T  (N ch ) in Relativistic Heavy Ion Collisions

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  1. Characteristics of pT (Nch) in Relativistic Heavy Ion Collisions Thomas S. Ullrich Brookhaven Nation Laboratory and Yale University February 9, 2003 • Modeling Initial Conditions • Hard and Soft in Elementary Collisions • STAR Results … • … and how they Compare to Models 19th Winter Workshop on Nuclear DynamicsBreckenridge, ColoradoFebruary 9 - 14, 2003

  2. Intriguing Ideas … Multiplicity Dependence of pt Spectrum as a Possible Signal for a Phase Transition in Hadronic Collisions L. Van Hove, PL 118B (1982) 138 pT  T vs. Nch plateau reflects Tc “If the plateau does not change [when changing incident energy], the deconfinement transition may be the correct explanation” Still a valid question: can we use simplest quantities measurable (soft physics)to learn about phase transition Thomas Ullrich, BNL

  3. Relating Nch and pT to Initial Conditions Initial conditions Dominant interactions at low Q2 (non-pQCD) Thermalization ? Equilibration? ? Nch, pT, s dependence Measurement In the absence of pQCD calculations we have to rely on models Thomas Ullrich, BNL

  4. Model Class I: Saturation Model(s) Overview: D. Kharzeev, et al. hep-ph/0204014 All partons within transverse area 1/Q2 participate coherently Density of partons: Probe interacts with partons with: s ~ as/Q2 srA << 1: dilute regime: pQCD srA >> 1: dense parton system srA 1 critical value, system looks dense for the probe: Qs2 ~ s(xGA(x, Qs2))/(RA2) dNch/d / (RA2)  Qs2/ s dNch/d / Npart  1/ s Relevant Scale:Qs2  dNch/d / (RA2) Thomas Ullrich, BNL

  5. Model Class II: Two Component Models “Soft”+”Hard” Kharzeev&Nardi PLB 507(2001)121 Wang&Hwa PRD 39(1989)187 Bass et al., nucl-th/0301087 Npart: Number of participants number of incoming nucleons (participants) in the overlap region Nbin: Number of binary collisions number of equivalent inelastic nucleon-nucleon collisions Thomas Ullrich, BNL

  6. How can we tell: Multiplicity Density ? Phys. Rev. C65, 31901R (2002) PRC 65 (2002) 061901 Au+Au @ 130 GeV dNch/dh / (Npart/2) Npart Some confusion: EKRT: final state saturation KL: initial state saturation KN: plain two-component model Thomas Ullrich, BNL

  7. How can we tell: Rapidity Density ? Gluon Saturation Model: Comparison: centrality and pseudorapidity dependence Model assumes: gluons from initial state directly  hadrons D. Kharzeev, et al., nucl-th/0108006 PHOBOS Thomas Ullrich, BNL

  8. Refined Saturation Models A different view on the consequences of gluon saturation: Gluon Saturation  Thermalization A.H. Mueller QM02 Thomas Ullrich, BNL

  9. First Look at pT: Effect of Jet Production on pT Wang&Hwa PRD 39(1989)187 ISR SppS Thomas Ullrich, BNL

  10. Second Look at pT: Energy and Beam Dependence Tevatron (1800 GeV) Akesson PLB119(1982)464 SppS (200 GeV) ISR pT at: Low Energy:little to no multiplicity and beam particle dependence High Energy:strong multiplicity and energy dependence Thomas Ullrich, BNL

  11. 0 10 20 30 40 charge multiplicity 0 10 20 30 40 charge multiplicity Third Look at pT: the Return of “Soft” and “Hard” CDF PRD 65 (2002) 072005 pp pT not corrected (pT > 0.4 GeV/c) ET>1.1GeV • Soft: pTonly depends on multiplicity (“sqrt”) • Note: Saturation Models: pT2  Nch • Hard: pT shows energies dependence and • multiplicity dependence (“linear”) Thomas Ullrich, BNL

  12. BBC Time Projection Chamber Magnet ZDC ZDC Au Au Coils BBC Silicon Vertex Tracker Central Trigger Barrel TPC Endcap & MWPC FTPCs 5% Central ZCal ZCal Endcap Calorimeter VertexPositionDetectors Barrel EM Calorimeter Central Trigger Barrel or TOF RICH STAR: Detector, Trigger & Runs Run I: Au+Au @ 130 GeV Run II: Au+Au @ 200 GeV p+p @ 200 GeV Run III: d+Au @ 200 GeV [p+p @ 200 GeV] Thomas Ullrich, BNL

  13. Getting the Geometry Right ZDC and ZDC vs. CTB not suited for classes s/stot < 0.20  divide ds/dNch distribution in multiplicity bins  find Npart and Nbin for these classes using Glauber calculations Thomas Ullrich, BNL

  14. Optical Glauber assume Woods-Saxon density profile integration of nuclear overlap function TAA(b) calculate probability to have n interactions at given b P(n, b) using only spp and TAA yields Nbin(b) and Npart(b) use two component-model including Gaussian fluctuations Problems: inaccurate stot (too small) MC Glauber nucleons are randomly distributed according to Woods-Saxon distribution nucleons in either nucleus are separated by distance d > dmin=0.4 fm interactions occur with a probability proportional to the overlap of the Gaussian nucleon density profile run for various b yields ds/dNbin, ds/dNpart, ds/db divide results into fractions of stot map to ds/dNch Glauber: MC vs. Optical Two approaches disagree: general agreement at RHIC  MC Thomas Ullrich, BNL

  15. Particle Efficiency & Background • High Efficiency (~80%) • Large Acceptance (~95%) • Corrected for (~10%): • Weak decay • Secondaries generated in detectors Thomas Ullrich, BNL

  16. Charged Hadron Spectra in Au+Au at 130 GeV That’s all you need to study pT and Nch Thomas Ullrich, BNL

  17. Back to Saturation vs. Two-Component Models STAR preliminary STAR preliminary Npart from MC Glauber Npart from Optical Glauber Difference significant not only at small Npart where model error are largest. Can we use dNch/dh/(2Npart) too really rule out models? Thomas Ullrich, BNL

  18. pT Centrality Dependence in Au+Au @ 130 GeV STAR preliminary 1. power law fit to spectra E d3/dp3  A (1+pT/p0) –n pT = 2p0/(n-3) 2. arithmetic mean (after extrapolation to pT = 0) pT can be derived from: Both identical within error bars Thomas Ullrich, BNL

  19. pT Multiplicity Dependence in 130 and 200 GeV saturation model scaling Consistent with flat: both Nch and pT Nch ratio: 1.190.05 (sys) pTratio: 0.99 0.02 (sys) Models do: not produce enoughpT not reproduce centrality shape We see no increase of <pT>  lose the early information? Maximum Missing Information  thermalization? Dominant Soft Interaction Contribution? Thomas Ullrich, BNL

  20. pT Dependence on sNN Saturation model: J. Schaffner-Bielich, et al. nucl-th/0108048 D. Kharzeev, et al. hep-ph/0111315 Saturation Model: Scaling doesn’t work for 130/200GeV data Thomas Ullrich, BNL

  21. pT Dependence on sNN due to Quenching ? Low pT Ratio quite flat Higher pT particle production depends on centrality, beam energy, pT Quenching not very different between 130 and 200 GeV Cronin more important? Thomas Ullrich, BNL

  22. Simple Superposition of “Soft”+”Hard” Nbin/( (Nch)AA/ (Nch)pp ) = 965/(690/2.5) = 3.5 pTs 0.366 GeV/c (from ISR) (pTpp-pTs)  RHIC energies – ISR = 0.390-0.366 GeV/c = 0.024 GeV/c But: (pTAuAu-pTs) = 0.517 – 0.366 GeV/c = 0.151 GeV/c(6.3×0.024 GeV/c) Two-component model appears to not work either Thomas Ullrich, BNL

  23. Characteristics of MeanpT OPAL PLB320(1994)417 e+e-: along the thrust axis agrees with JETSET calculation • AA: can not be treated as superposition of more elementary collisions • pp: can not be treated as superposition of more elementary collisions e+e-: pure jets pp: soft+hard AA: ???+FSI M. Szczekowski PRD 44 (1991) R577 Thomas Ullrich, BNL

  24. Work in Progress: d+Au • d+Au Analysis: Cronin/shadowing+less Quench vs Gluon Saturation CGC XN Wang Accardi hep-ph/0212148 px1GeV/c Thomas Ullrich, BNL

  25. Conclusions • Nch centrality and energy dependence not sufficient to discriminate between models • pT from AA has characteristic energy dependence • NOT a simple superposition of more elementary collisions • Comparison with Models • Saturation (no scaling between pT and Qs)  fails • Two-component (not enough pT ) fails • Hijing and RQMD do not get close at all fails • Is thermalization only viable explanation? • More Study (beam energy, species) desperately needed • Effect of jet/minijet production • Gluon Saturation? • Note: what happened at high-pT is not directly relevant Thomas Ullrich, BNL

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