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.

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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?

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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

,,

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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)]

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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.

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String Fragmentation

Extract PYTHIA parton showers evolved to a scale Q0. Standard PYTHIA Lund string fragmentation:

Rainer Fries

Lund String

String Decay

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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

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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

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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

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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-

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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

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Adding Shower-Thermal Recombination

Pions and protons at RHIC. Thermal-thermal added.

Baryon production clearly enhanced by shower-thermal recombination.

Rainer Fries

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Baryon Enhancement

Proton/pion ratio is enhanced by shower-thermal recombination.

Rainer Fries

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Baryon Enhancement

Very similar picture for LHC.

Rainer Fries

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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

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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

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Backup

Rainer Fries

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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.