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Dynamical Modeling of Relativistic Heavy Ion Collisions

Dynamical Modeling of Relativistic Heavy Ion Collisions. Tetsufumi Hirano. Work in partly collaboration with Y.Nara (Frankfurt), M.Gyulassy (Columbia). Workshop at RCNP, Nov 4, 2004. The Five Pillars of RHIC Wisdom. Slide from T.Hallman Talk@ICHEP04 ~STAR white paper. Ideal hydro.

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Dynamical Modeling of Relativistic Heavy Ion Collisions

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  1. Dynamical Modeling of Relativistic Heavy Ion Collisions Tetsufumi Hirano Work in partly collaboration with Y.Nara (Frankfurt), M.Gyulassy (Columbia) Workshop at RCNP, Nov 4, 2004

  2. The Five Pillars of RHIC Wisdom Slide from T.Hallman Talk@ICHEP04 ~STAR white paper Ideal hydro Early thermalization + soft EOS Statistical model Quark recombination  constituent q d.o.f. …suggest appealing QGP-based picture of RHIC collision evolu-tion, BUT invoke 5 distinct models, each with own ambigu-ities, to get there. u, d, s equil-ibration near Tcrit pQCD parton E loss CGC Very high inferred initial gluon density Very high anticipated initial gluon density

  3. Hydro: 0, freezeout, boost-invariance ambigs. Statisticalmodel: equilib’n or phase space? LQCD: CPU limitations; applic’y to dynamic matter? Gluon saturation: universal scale estab-lished? Quark recomb.: predictive power? Parton E loss: untested assump-tions Slide from T.Hallman Talk@ICHEP04 ~STAR white paper The State of RHIC Theory A patchwork, with model parameters adjusted independ-ently for each element Emerging description of beautiful evolution from one new state of matter to another! And Yet, In order to rely on theory for compelling QGP discovery claim, we need:greater coherence; fewer adjusted parameters; quantitative estimates of theoretical uncertainties

  4. Hairsplitting Comments from Our Approach How are these consistent with each other? Discussion from hydrodynamic point of view: • Hydro vs. Statistical model (main topic) • Hydro vs. Recombination model • Hydro vs. Jet tomography • Hydro vs. CGC These discussions will tell us what to do next and lead to a unified understanding of HIC.

  5. Today’s Bad News The elliptic flow at RHIC is “accidentally” reproduced by a hydro model.

  6. Hydro vs. Statistical Model (1) • Statistical model Tch>Tth • (conventional) hydro Tch=Tth • No reproduction of ratio and spectra simultaneously Chemical parameters  particle ratio Thermal parameters pt spectra

  7. Hydro vs. Statistical Model (2) P.Huovinen, QM2002 proceedings

  8. Hydro vs. Statistical Model (3) • Single Tf in hydro • Hydro works? • Both ratio and spectra? Introduction of chemical potential for each hadron! mi

  9. Hydro vs. Statistical Model (4) EOS Partial chemical equilibrium (PCE) Example of chem. potential T.H. and K.Tsuda(’02) Expansion dynamics is changed (or not)? t

  10. Hydro vs. Statistical Model (5) Contour(T=const.) T(t) at origin Model CE <vr>(Tth) Model PCE T.H. and K.Tsuda(’02) t

  11. Hydro vs. Statistical Model (6) • How to fix Tth in conventional hydro • Response to pT slope • Spectrum harder as decrease Tth • Up to how large pT? • Tth independence of slope in chemically frozen hydro • No way to fix Tth • Suggests necessity of (semi)hard components Charged hadrons in AuAu 130GeV

  12. Hydro vs. Statistical Model (7) Partial Chemical Equilibrium Chemical Equilibrium p Kolb and Heinz(’04) K p Is v2(pT) sensitive to the late dynamics? T.H. and K.Tsuda (’02)

  13. Hydro vs. Statistical Model (8) Generic feature! pdV work + (number) /(entropy) t t Slope of v2(pT) ~ v2/<pT> Response todecreasing Tth (or increasing t) t

  14. Hydro vs. Statistical Model (9) Simplest case: Pion gas Longitudinal expansion  pdV work! CFO: dS/dy = const. • dN/dy = const. • <pT> decreases CE: dS/dy = const. • dN/dy decreases (mass effect) • <pT> can increase as long as <ET>dN/dy decreases. dET/dy should decrease with decreasing Tth.  <ET>dN/dy should so.

  15. Hydro vs. Statistical Model (10) PHENIX white paper, nucl-ex/0410003

  16. Hydro vs. Statistical Model (11) • Choice of Tth in conventional hydro results from neglecting chemical f.o. • The great cost one has to pay for “simplification”! • Importance of chemical potential for each hadrons within hydrodynamics • “No-Go theorem”. Yet you use? • >90% hydro results at SPS and RHIC do not make sense! • Chemical eq. mimics viscous hydro?

  17. Today’s Good News Currently, hydro+cascade is the only model which reproduces the elliptic flow, particle ratio, and particle spectra. D.Teaney et al., nucl-th/0110037. Caveat: Need realistic interfaceand oversampling to get rid of numerical artifacts.

  18. Hydro vs. Recombination (1) Today, I won’t discuss (violation of) energy conservation, decrease of entropy… reco(Duke) R.J.Fries et al. (’03) T.H. and K.Tsuda (’02) Half of radial flow comes from hadron phase in hydro Tc=175MeV & vT = 0.55??? Parameter dependence?

  19. Hydro vs. Recombination (2) Soft+hard reco is important? Naïve idea: Hydro+jet model with recombination via string fragmentation Only mass effect T.H.,QM2004 PHENIX “model killer” plot! nucl-ex/0408007 Pick up a parton from QGP Associated yield 1.7<pT<2.5GeV/c

  20. Hydro vs. Jet Tomography (1) T.H. and Y.Nara (’04) I.Vitev, nucl-th/0404052 Input: dNch/dh Output: Input: RAA Output: consistent?

  21. Hydro vs. Jet Tomography (2) Hydrodynamics: Parton density Jet tomography: “Color charge density” cf.) Parton density in chem. eq. (Nf=3), (Nf=2) > < Not complete chem. eq.!  Need chemical non-eq. description rate eq. for ng and nq

  22. Hydro vs. CGC (1) Gluons produced from two CGC collisions (KLN) Kharzeev and Levin (’01) T.H. and Y.Nara(’04) ET/N ~ 1.6 GeV • Consistent with classical Yang Mills on 2D lattice (KNV, Lappi) • Inconsistent with exp. data ~0.6GeV

  23. Hydro vs. CGC (2) Initial condition of hydrodynamic simulations Gluons produced from two CGC collisions (KLN) Final (psuedo)rapidity spectra of all hadrons ET/N ~ 1.6 GeV ET/N ~ 1.0 GeV ET/N ~ 0.55 GeV  Consistent with classical Yang Mills on 2D lattice (KNV)  Consistent with exp. data ~0.6 GeV This should be obtained through non-equilibrium processes.  Production of entropy Hydrodynamic evolution “PdV work” reduces ET/N.

  24. Hydro vs. CGC (3) • Need a mechanism to reduce ET/N ? • ET and/or N • Non-equilibrium description is extremely important. • Can we get a short thermalization time (~1fm/c)? • Is Boltzmann (elastic+inelastic) sufficient for this? • If not, may we need non-eq. quantum field approaches?

  25. Summary so far We should keep in mind in modeling of HIC: • “The right model in the right place” basis • Time scale • Energy/momentum scale • Consistency among models • Treatment of interface among models • The number of parameters/assumptions as small as possible

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