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Recombination for JET Shower MC: Status and Discussion

JET NLO & MC Meeting Wayne State University , August 23, 2013. Recombination for JET Shower MC: Status and Discussion. Rainer Fries Texas A&M University. On Behalf O f Kyongchol Han Che -Ming Ko. Hadronization. Hadronization = difficult, non- perturbative problem

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Recombination for JET Shower MC: Status and Discussion

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  1. JET NLO & MC Meeting Wayne State University, August 23, 2013 Recombination for JET Shower MC:Status and Discussion Rainer Fries Texas A&M University On Behalf Of Kyongchol Han Che-Ming Ko

  2. Hadronization • Hadronization = difficult, non-perturbative problem • Sometimes we can apply one of two extreme limits in which hadronization becomes simpler: • Universality at large momentum  single-particle fragmentation: fragmentation functions can be measured. • Universality at low momenta  thermalization: equation of state, can be calculated on the lattice. • In between: universality broken, hadronizationsystem-dependent. JET NLO&MC 2013

  3. Hadrons in Heavy Ion Collisions • Proton/pion ratio • RAA • Intermediate momentum region in heavy ion collisions (2-8 GeV): • No kinetic equilibrium • Multi-particle dynamics • No microscopic description of partondynamics. JET NLO&MC 2013

  4. Why Quark Recombination? • Data indicates a dependence of several important observables on the number of valence quarks. • Quark coalescence models very successful for hadron production at intermediate PT in HICs. • Large baryon/meson ratios • Elliptic flow scaling with quark number  QGP signature? JET NLO&MC 2013

  5. Quark Recombination • Start from a distribution of quarks • Instantaneous approximation: 2  1, 3  1 • Finite time: recombination rate equations ? JET NLO&MC 2013

  6. Recombination in Jet Showers • JET goal related to NSAC Performance Measures: Complete realistic calculations of jet production in a high energy density medium for comparison with experiment. (DM7) • This includes chemical composition • Well-established hadronization models for vacuum shower Monte-Carlo’s • Lund string fragmentation • Cluster hadronization • How to generalize to jets in a medium? • Recombination: some early work on vacuum showers. • Challenge: get vacuum fragmentation right. • Advantage: medium effects are straight forward to implement; does well with heavy ion single particle spectra. [R. Migneron, M. E. Jones, K. E, Lassila, PLB 114, 189 (1983)] [R.C. Hwa and C.B. Yang, PRC 70, 024904 (2004); 024905 (2004)] JET NLO&MC 2013

  7. Formalism: Overview • Challenges: • Calculate parton showers in a controlled way; vacuum or medium modified. • Need event-by-event formalism; momentum and energy conservation in each shower are important. • Want to include space-time information. • Established work flow: • Here: We use parton and hadron showers from PYTHIA as a testing ground. • No space-time information. Add minimum non-perturbative effects: gluon splitting Perturbativeparton shower (PYTHIA, HERWIG, JET MCs) Apply instantaneous quark recombination w/ phenomenological meson and baryon Wigner functions. Recombine into full hadronic resonance spectrum and decay; treat remnant partons. Sample quarks from thermal medium in which jet is embedded. JET NLO&MC 2013

  8. String Fragmentation • Extract PYTHIA parton showers evolved to a scale Q0. • Standard PYTHIA Lund string fragmentation: Lund String String Decay JET NLO&MC 2013

  9. Recombination + Remnant Strings • Extract PYTHIA parton showers evolved to a scale Q0. • Standard PYTHIA Lund string fragmentation: • Our approach: Lund String Force gluon decay String Decay Recombine Remnant strings String Decay JET NLO&MC 2013

  10. Recombine Quarks • Use instantaneous recombination model by Greco, Ko, Levai: • Baryon and meson Wigner functions • Here M = 0.24 GeV, B = 0.35 GeV JET NLO&MC 2013

  11. Recombine Quarks • In absence of space-time information integrate out spatial coordinates in the Wigner functions. • Direct recombination produces hard spectra. • Allow recombination into resonances with subsequent decay • Mesons: π, ρ, a1, K, K*, and K1 • Baryons N, N’, Δ, and Δ’ • Reconnect remnant quarks by short strings that fragment. JET NLO&MC 2013

  12. Results • PYTHIA 100 GeV jets: • Recombination probability: JET NLO&MC 2013

  13. Event-By-Event Vacuum Fragmentation • Reproduction of vacuum fragmentation compares favorably to PYTHIA string fragmentation. • Lessons learnt: • Resonances important. • Event-by-event calculation important. 100 GeV light quark jets in e++e- [K. Han, C.M. Ko, R.J.F., arxiv:1209.1141] JET NLO&MC 2013

  14. Adding Medium Partons • Sampling thermal partons from a blastwave model (T=170 MeV, <v> = 0.6 (0.65)). • Allow recombination of thermal partons Recombine Remnant strings JET NLO&MC 2013

  15. Adding Shower-Thermal Recombination • Pions and protons at RHIC. • Thermal-thermal added. • Baryon production clearly enhanced by shower-thermal recombination. JET NLO&MC 2013

  16. Baryon Enhancement • Proton/pion ratio is enhanced by shower-thermal recombination. JET NLO&MC 2013

  17. Baryon Enhancement • Very similar picture for LHC. JET NLO&MC 2013

  18. Plans for the Near Future • Additional tests … • E.g. broadening variables • Similar tests done for parton shower MCs? • So far tested against PYTHIA. Next step: new shower MC + recovs data • Protocol for interface with parton shower MCs. • Role of spatial coordinates? • Replace blastwave by hydro. JET NLO&MC 2013

  19. Merging of Modules • First step: take vacuum showers from “HT-MC” including space-time information. • Need access to a database of vacuum events. • Hadronization module assumes that full space-time information x is available. • This will allow us to test recombination with space-time information. • List of items to agree on for medium shower: • Shower MC needs to provide identifier of hydro event used. • Hadronization expects full information on space-time point x. • Space-time point = point of last splitting? • Shower medium effects restricted to T< Tc. • Partons that “stop” inside QGP will be propagated to the critical hypersurface by the hadronization module. • Recombination + remnant fragmentation applied to partons at T=Tc and T> Tc. JET NLO&MC 2013

  20. Backup JET NLO&MC 2013

  21. Recombination in Equilibrium • Realistic hadronizationhypersurface: • Extract equal-time quark phase space distributions fq along  from hydro or kinetic model. • Apply RRM cell-by-cell  meson phase space distribution fM along . • Compute meson current across  a la Cooper-Frye: • Result for charm-light system using AZHYDRO: t = const. [He, RJF & Rapp, 1106.6006 [nucl-th]] JET NLO&MC 2013

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