recombination for jet shower mc: status and discussion rainer fries texas a&m university jet nlo...
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Recombination for JET Shower MC:
Status and Discussion
Rainer FriesTexas A&M University
JET NLO & MC MeetingWayne State University, August 23, 2013
On Behalf Of Kyongchol HanChe-Ming Ko
JET NLO&MC 2013 2
Hadronization
Rainer Fries
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, hadronization system-dependent.
JET NLO&MC 2013 3
Hadrons in Heavy Ion Collisions
Rainer Fries
Proton/pion ratio
RAA
Intermediate momentum region in heavy ion collisions (2-8 GeV): No kinetic equilibrium Multi-particle dynamics No microscopic description of parton dynamics.
JET NLO&MC 2013 4
Why Quark Recombination?
Rainer Fries
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
Rainer Fries
?
PMPMPd
NM ;;)2( 3
3
pgptfptft M
pM
,,
JET NLO&MC 2013 6
Recombination in Jet Showers
Rainer Fries
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
Rainer Fries
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
Perturbative parton shower (PYTHIA, HERWIG, JET MCs)
Apply instantaneous quark recombination w/ phenomenological meson and baryon Wigner functions.
Sample quarks from thermal medium in which jet is embedded.
Recombine into full hadronic resonance spectrum and decay; treat remnant partons.
JET NLO&MC 2013 8
String Fragmentation
Extract PYTHIA parton showers evolved to a scale Q0. Standard PYTHIA Lund string fragmentation:
Rainer Fries
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:
Rainer Fries
Lund String
Force gluon decay
Recombine
String Decay
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
Rainer Fries
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.
Rainer Fries
NππNρΔNπΔ
NππNρNπN
KππKρKKK
a*
(1600) ,
(35%) (65%),(1440)
(1270)
1
1
1
JET NLO&MC 2013 12
Results
PYTHIA 100 GeV jets:
Recombination probability:
Rainer Fries
JET NLO&MC 2013 13
Event-By-Event Vacuum Fragmentation
Rainer Fries
Reproduction of vacuum fragmentation compares favorably to PYTHIA string fragmentation.
Lessons learnt: Resonances important. Event-by-event calculation important.
[K. Han, C.M. Ko, R.J.F., arxiv:1209.1141]
100 GeV light quark jets in e++e-
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
Rainer Fries
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.
Rainer Fries
JET NLO&MC 2013 16
Baryon Enhancement
Proton/pion ratio is enhanced by shower-thermal recombination.
Rainer Fries
JET NLO&MC 2013 17
Baryon Enhancement
Very similar picture for LHC.
Rainer Fries
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 + reco vs data
Protocol for interface with parton shower MCs. Role of spatial coordinates?
Replace blastwave by hydro.
Rainer Fries
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.
Rainer Fries
JET NLO&MC 2013 20
Backup
Rainer Fries
JET NLO&MC 2013 21
Recombination in Equilibrium
Rainer Fries
[He, RJF & Rapp, 1106.6006 [nucl-th]]
Realistic hadronization hypersurface : 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:
dd
t = const.
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