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Tom Humanic Ohio State University WPCF 08 Krakow

Review on initial conditions that allow for a successful description of the RHIC data on spectra, V2, (as)HBT, etc…. Tom Humanic Ohio State University WPCF 08 Krakow. Outline. Brief description of model --> initial conditions and a few details

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Tom Humanic Ohio State University WPCF 08 Krakow

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  1. Review on initial conditions that allow for a successful description of the RHIC data on spectra, V2, (as)HBT, etc… Tom Humanic Ohio State University WPCF 08 Krakow

  2. Outline • Brief description of model --> initial conditions and a few details • Comparison of model calculations with RHIC experiments STAR, PHENIX, and PHOBOS • Predictions for LHC Pb+Pb

  3. Simple superposition-rescattering model for A+A collision Initial p+p “thin disk” of radius r = 1 fm i-th particle j-th pp collision A A * Superimpose f*A PYTHIA pp events, where f=overlap fraction for impact param. * Assume all particles have the same proper time for hadronization, t, so that the hadronization space-time for each particle is given by “causality”, i.e. ti = t Ei/mi ; xi = xoi + t pxi/pi ; yi = yoi + t pyi/pi ; zi = t pzi/pi * Perform hadronic rescattering using a full Monte Carlo rescattering calculation

  4. Other details of the model…. • Use PYTHIA v.6409 to generate hadrons for 200 GeV (and 5.5 TeV) p+p “minimum bias” (non-elastic and non-diffractive) events “final” hadrons from PYTHIA to use:  p, K, N, D , L , w, r, K*’ • Use mult > 20 (38 for LHC) cut on p+p events --> cuts out ~ 20-25% of events and helps dn/dagree better with PHOBOS 200 GeV/n Au+Au • Monte Carlo hadronic rescattering calculation: Let hadrons undergo strong binary collisions until the system gets so dilute (since it is expanding) that all collisions cease. --> (i,j) from Prakash, etc.. Record the time, mass, position, and momentum of each hadron when it no longer scatters.  freezout condition • Take  = 0.1 fm/c for all calculations --> found to agree with Tevatron HBT data (T.J.H., Phys.Rev.C76,2007)

  5. Advantages of this model • Well-defined initial conditions: PYTHIA for kinematics and causality for geometry • Jets are built into the model via PYTHIA so high-pt observables can be studied • Initial conditions easily scalable to LHC energies for predictions there • Simplicity -- hadrons+geometry+rescattering with a few well-defined parameters Disadvantages of this model • Simplicity -- Surely leaves out some early-phase physics, e.g. quark and gluon degrees of freedom • Therefore, will be satisfied to get a qualitative description of trends of at least some experimental observables

  6. Comparisons with RHIC experiments • Made a 90K event 200 GeV/n Au+Au minimum bias run with model --> apply centrality cuts (via multiplicity cuts) and kinematic cuts to this run to make “absolute comparisons” with experiments • Comparisons made with published 200 GeV/n Au+Au experimental results: - spectra with PHOBOS, PHENIX and STAR - V2 with STAR and PHOBOS - HBT and as-HBT with STAR - Raa with PHENIX - jet-suppression with STAR

  7. Spectra: Model vs PHOBOS, PHENIX, and STAR

  8. V2 vs. centrality, pt, and eta Model vs. STAR and PHOBOS

  9. V2 vs. pt --> large pt: Model vs. STAR

  10. V2 vs pt --> pi, K, p: Model vs. STAR

  11.  HBT from Model: projections --> qout, qside, qlong

  12. Azimuthal  HBT: Model vs. STAR

  13.  HBT vs. kt: Model vs. STAR

  14. Raa vs. pt: Model vs. PHENIX

  15. Jet suppression -->dn/d , all charged particles, -0.7<<0.7 pt trigger>4 GeV/c, pt>2 GeV/c, 200 GeV/n Au+Au Model vs. STAR (minimum bias case) (lines are fits to model points)

  16. LHC Pb+Pb predictions from this model • Use PYTHIA 5.5 TeV p+p collisions as input • Make multiplicity cut on p+p collisions > 38, cuts out ~20% of p+p events (comparable to multiplicity cut used for RHIC Au+Au) • Substitute 197 --> 208 • Make a minimum bias run with model for 800 Pb+Pb events • Show predictions for spectra, V2, and HBT

  17. Model predictions for spectra, 5.5 TeV/n Pb+Pb

  18. Model prediction for V2 vs. pt, 5.5 TeV/n Pb+Pb

  19. Model predictions for  HBT, 5.5 TeV/n Pb+Pb

  20. Conclusions • The present simple hadronic rescattering model qualitatively describes the trends for a range of experimental results for 200 GeV/n Au+Au collisions at RHIC • This suggests that the hadronization proper time in these collisions is short, ~ 0.1 fm/c • Predictions from this model for LHC Pb+Pb collisions suggest: - dn/d ~ 1400 for charged hadrons at mid-rapidity for central collisions - V2 may be comparable or somewhat less than that at RHIC -  HBT may give ~ 20-30% higher radius parameters compared to RHIC

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