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NEWS FROM MICROSCOPIC MODELS ON STRANGENESS IN ULTRARELATIVISTIC HEAVY ION COLLISIONS

NEWS FROM MICROSCOPIC MODELS ON STRANGENESS IN ULTRARELATIVISTIC HEAVY ION COLLISIONS. Sven Soff (LBNL). Overview ( strange interests in the past ~1.5 years). double-strange -meson (re)investigating the ideas from the 80‘s (P.Koch, B.M üller, J.Rafelski, PR 142 (1986) 1)

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NEWS FROM MICROSCOPIC MODELS ON STRANGENESS IN ULTRARELATIVISTIC HEAVY ION COLLISIONS

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  1. NEWS FROM MICROSCOPIC MODELS ON STRANGENESS IN ULTRARELATIVISTIC HEAVY ION COLLISIONS Sven Soff (LBNL) Sven Soff

  2. Overview (strange interests in the past ~1.5 years) • double-strange -meson (re)investigating the ideas from the 80‘s (P.Koch, B.Müller, J.Rafelski, PR 142 (1986) 1) messenger of the early phase of the system evolution production, spectra, late stage interactions What do we learn from -mesons ? Sven Soff

  3. Overview II(strange interests in the past ~1.5 years) • Field effects on the dynamics of the multi-particle system; in particular, on strange hadrons. • other interesting studies (for example, detailed balance on the many-body level, strangeness excitation functions, problems of the quark/diquark string model, initial conditions from a selfconsistent approach, etc...) • Summary & Outlook Sven Soff

  4. dynamical description of hadronization only quarks, no gluons describe nonperturbative soft regime interaction via two-body color potentials approximation: fixed charges for large baryon number, low gluon density (GSI-future) qMD - quark molecular dynamics(Scherer et al., NJP 3 (2001) 8) Sven Soff

  5. Cornell-potential (incl.confinement) Comparison to exp. data surprisingly good Strangeness distillation in quark phase (S. Scherer et al.) qMD, S-distillation Sven Soff

  6. Study reclustering vs. rearrangement Different diffusion lengths (path length of quark cluster before hadron formation) 2.2 fm for recombination 4.8 fm for rearrangement S+Au @ 200 AGeV see also R.Fries et al., nucl-th/0301087 recombination vs. fragmentation @RHIC Hadronization in qMD Rearrangement vs. Recombination (Scherer et al., NJP 3 (2001) 8) Sven Soff

  7. Sven Soff

  8. Transverse Momentum Generation From the decay of color strings: f(pt) ~ exp(-pt2/ 2) with =0.55GeV/c for elementary reactions. In general, the Schwinger mechanism does not only produce massive particles but also pt from the linear energy density  Pi~ exp [-(mi2+pt2) / ] = exp [-mi2/ ]* exp [-pt2 / 2int] Related also to, for example, CGC picture: Heavy ion data (spectra) follow simple scaling law <pt>2 ~ Nchdue to intrinsic pt broadening. J.Schaffner, L.McLerran, D.Kharzeev, R.Venugopalan, PLB514 (2002) 29, NPA705 (2002) 494 Sven Soff

  9. Formation times and  . Sven Soff

  10. Color Field Strength & Regge Slope Regge trajectory J(M)=(0) + ‘ M2 with ‘  1 GeV-2 for resonances. In rotational string picture J=1/(2) M2 =1/(2 ) 1GeV/fm   ‘ Pomeron exchange results in ‘P  0.4 GeV-2 This translates into an effectively enhanced color field strength  Sven Soff

  11. dN/dy ( , ptint ) for -mesons (S.Soff, K. Kesavan, N. Xu) • Yields depend strongly on color field and intrinsic pt • Relative contributions (meson-meson vs. direct) also depend strongly on  and ptint Sven Soff

  12. Transverse momentum spectra of -mesons • With increasing intrinsic pt the spectra get harder and direct production dominates Sven Soff

  13. Mean pt – mass dependence • <pt> increases approx. linearly with m • exp: <pt>() = <pt>(p); theo: <pt>() < <pt>(p); • difference due to rescattering of daughters Sven Soff

  14. Hadron Ratios • Strange particle ratios strongly increase with  • -ratios decrease with increasing ptint (reduced coalescence production) • p/ increases with ptint (energy-dependent ppbar annihilation) ; stronger increase for =3 than for =1 (due to larger particle densities, i.e., stronger absorption) ptint (S.Soff, K. Kesavan, N. Xu) Sven Soff

  15. Baryon Ratios • Ratios increase with strangeness content |S| • Ratios increase with impact parameter (less stopping & absorption) • Ratios increase with color field strength  (pair production vs. stronger baryon transport) (S.Soff, J.Randrup, H.Stöcker, N. Xu, PLB551 (2003) 115 ) Sven Soff

  16. Netbaryon distributions • Stronger rapidity shift through SCF (particle densities and formation times) • More netbaryon, same number of netprotons, that is, hyperonization. • (-bar)/(p-pbar) enhanced from ~0.45 to 0.8 in SCF scenario. (S.Soff, J.Randrup, H.Stöcker, N. Xu, PLB551 (2003) 115 ) Sven Soff

  17. QGSM • -meson yield under- estimated by a factor 2 • String fusion even reduce yields ? • Slope and flow compatible with data (reason? „sufficient secondary scatterings due to increased initial particle densities; these are caused by multi-pomeron exchanges + hard processes“) (strings are nonparallel to beam axis) L.Bravina et al., NPA715 (2003) ; E.Zabrodin et al., PLB508 (2001) 184 Sven Soff

  18. Parton Cascades • VNI/BMS: numerous new results after putting it on solid grounds • Example: baryon stopping • conventional explanation of baryon transport (initial state + parton rescattering) • question: why does longitudinal dynamics not imply transverse dynamics (v2)? S.A. Bass, B. Müller, D. Srivastava, nucl-th/0212103 Sven Soff

  19. Initial and late  production initial (t<5 fm/c) production followed up by late stage coalescence-like production in K anti-K reactions • JPG 27 (2001) 449 Sven Soff

  20. AMPT – Discussing the -puzzle • Systematic stuy of: K+K- vs. +- (NA49,NA50) in-medium effects • Yield differences in both channels cannot fully be explained • Importance of production via K Kbar rescattering of decay kaons • Additional initial production needed ! • Initial‘s primary visible in dimuon channel ! S.Pal, C.M. Ko, Z. Lin, NPA707 (2002) 525 S.Soff et al JPG2001; S.Johnson et al EPJC2001 Sven Soff

  21. ExcitationFunctions – Bulk Strangeness Production Systematic Study of Particle Production in pp and AA from SIS/AGS to SPS (HSD & UrQMD) • Overestimation of pions; kaons reasonable (multiparticle back reactions, enh.  in-medium mass) H.Weber, E.Bratkovskaya, W.Cassing, H.Stöcker, PRC67 (2003) 014904 Data: NA49 & E866,E917 Sven Soff

  22. Multiple Meson Fusion Reactions and Antibaryon Production • Strong flavor rearrangement reactions like approximate description of anti-p at AGS/SPS through multiple interactions of formed hadrons chemical equil. reached by quark/flavor rearrangement W.Cassing, NPA700 (2002) 618 R.Rapp,E.Shuryak & C.Greiner,S.Leupold Sven Soff

  23. Parton based Gribov-Regge TheoryH.Drescher, M.Hladic, S.Ostapchenko, T.Pierog, K.Werner, PR350 (2001) 93 • selfconsistent description of energy sharing • initial conditions for AA + pp • (multi-)pomeron exchange to describe both soft and hard processes. NEXUS3 see also discussion of bar/ ~ 1: due to combinatorics + finite size effects diquark-quark model pushed over its limits? M.Bleicher, F.Liu, J.Aichelin, K.Werner et al., PRL88 (2002) 202501 Sven Soff

  24. J/ suppression reviewed • Reanalysed NA50 data show rather smooth decrease • Data now almost agree with model predictions • Suppression purely on hadronic level? C.Spieles et al., PRC60 (1999) 054901 Sven Soff

  25. Strongcolor fields are associated with (i) enhanced heavy flavor, diquark production probabilites, (ii) modified, shorter formation times, (iii) stronger intrinsic transverse momentum Effects on -mesons: (a) enhanced yields (b) change of the composition of spectra (c) hardening of spectra (d) mean pt increase (e) particle ratios (f) baryon dynamics Moreover: role of late stage vs. early producion, rescattering of decay daughters Differences between kaonic and muonic -mesons wanted ! Summary Sven Soff

  26. quark Molecular Dynamics (qMD) provides a (simple) dynamical description of hadronization dynamics in soft regime. needs to be tested! Parton Cascades technically established; learn about the validity range of pQCD, or necessary modifications. (see also talk of D. Molnar) Excitation functions essential to detect deficiencies in models other new developments: - multi-particle collisions - charm in microscopic models - initial conditions in a field theoretical language (parton ladders) Summary II Sven Soff

  27. Test of thermodynamic properties by infinite matter simulations pA (for example, RHIC) Exact understanding of v2 (collision numbers, formation times) How is the (partially) hydrodynamic behavior realized on a microscopic level? Different approaches to explain partial success of hybrid/pure hydro Charm production @RHIC (E.Bratkovskaya,W.Cassing, H.Stöcker, nucl-th/0301083) analogy to strangeness: DDJ/+X Outlook (not discussed here) Sven Soff

  28. Particle Correlations (no talk about HBT today....) HBT-puzzle: STAR data with improved Coulomb corrections (D.Margesto/CERES) closer to QGP+hadronic rescattering for the first 2-3 low pt-bins. see, for example, talks by R. Lacey, Z.W. Lin , F. Retiere, S.Bekele. Outlook II NPA (2003) Sven Soff

  29. Stefan Scherer Sven Soff

  30. Sven Soff

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