Download Jet hadronization and E-by-E issues in energy loss

RHIC Strategy Meeting
Wayne State University, August 24, 2013
Uncertainties in jet event
generators due to hadronizaton
scheme, Other issues with energy
loss on E-by-E hydro, and the
extraction of transport
coefficients
Rainer Fries
Texas A&M University
RHIC Strategy Meeting
Wayne State University, August 24, 2013
Hadronization, Chemistry
and Other Issues
Rainer Fries
Texas A&M University
Hadronization

Hadronization: Challenge or Opportunity?
HQ sector
 Quark number scaling


Extraction of Jet/High-PT Physics:


JET Hadronization Module
Flavor conversions revisited
Rainer Fries
RHIC Strategy 2013
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Hadrons in Heavy Ion Collisions

Proton/pion ratio

RAA

“Universal” hadronization in thermalized (low PT) and pure fragmentation (high
PT) region.
Intermediate momentum region in heavy ion collisions (2-8 GeV):


No kinetic equilibrium; Multi-particle dynamics; No microscopic description of parton
dynamics.
Rainer Fries
RHIC Strategy 2013
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Can Hadronization Tell Us About QGP?

Example: Quark Number dependent phenomena

Usual interpretation: quark degrees of freedom were active in the collision.
Rainer Fries
RHIC Strategy 2013
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Heavy Quark Sector I

Recombination forces heavy quarks to feel the collective flow.
Charm to D-meson coalescence in a recombination model with correct equilibrium limit.
 Recombination rate ~ c+light quark elastic scattering rate near Tc.

Rainer Fries
RHIC Strategy 2013
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Heavy Quark Sector II

Flavor effects in the heavy quark sector: Ds vs D

Changes in chemistry are often hadronization effects.
Rainer Fries
RHIC Strategy 2013
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C. Suarez (STAR), poster, QM2008
inclusive Au+Au: M. Lamont (STAR) SQM06
Cu+Cu: C. Nattrass (STAR), QM2008
Au+Au: J.B. (STAR), WWND07
Chemistry in Jet and Ridge
pTtrig > 4.0 GeV/c
2.0 < pTassoc < pTtrig
Au+Au: 2<pTtrig<3 GeV/c,Cu+Cu:3<pTtrig<6 GeV/c
PHENIX, arXiv:0712.3033
Rainer Fries
Jana Bielcikova
Baryon/meson ratios:
•“jet”: smaller than inclusive
and similar to p+p
• ridge: similar to inclusive
RHIC Strategy 2013
Jana Bielcikova, Hard Probes 82008
Recombination in Jet Showers

JET goal: jet shower Monte Carlo including medium-modified hadronization

Well-established hadronization models for vacuum shower Monte-Carlo’s
Lund string fragmentation
 Cluster hadronization
 How to generalize to jets in a medium?


Recombination
Challenge: get vacuum fragmentation right.
 Advantage: medium effects are straight forward to implement; does well with heavy ion
single particle spectra.
 Need event-by-event formalism; momentum and energy conservation in each shower are
important.
 Need to include space-time information.

Rainer Fries
RHIC Strategy 2013
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String Fragmentation


Here: PYTHIA parton showers, will eventually work with MM showers
Standard PYTHIA Lund string fragmentation:
Lund String
String Decay
Rainer Fries
RHIC Strategy 2013
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Recombination + Remnant Strings


Here: PYTHIA parton showers, will eventually work with MM showers
Standard PYTHIA Lund string fragmentation:
Lund String

Our approach:
Force gluon decay
String Decay
Recombine
Remnant strings
String Decay
Rainer Fries
RHIC Strategy 2013
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Recombine Quarks

In absence of space-time information integrate out spatial coordinates in the
Wigner functions.

Monte-Carlo implementation of recombination probabilities

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
RHIC Strategy 2013
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Event-By-Event Vacuum Fragmentation

Reproduction of vacuum fragmentation compares favorably to PYTHIA string
fragmentation.
+ 100 GeV light quark jets in e +e
[K. Han, C.M. Ko, R.J.F., arxiv:1209.1141]

Lessons learnt:
Resonances important.
 Event-by-event calculation important.

Rainer Fries
RHIC Strategy 2013
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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
Recombine
Remnant strings
Rainer Fries
RHIC Strategy 2013
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Shower-Thermal Recombination

Pions and protons at RHIC.
Thermal-thermal added.

Baryon production clearly enhanced by shower-thermal recombination.

Rainer Fries
RHIC Strategy 2013
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Recover Baryon Enhancement

Proton/pion ratio is enhanced by shower-thermal recombination.
Rainer Fries
RHIC Strategy 2013
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Lessons So Far?

Hadronization effects in jets: too early to tell the full story

Extrapolating from heavy quarks: jet-thermal recombination adds a layer of
diffusion and makes “hard” hadrons feel collective flow.
Broadening?
 Larger v2?

Rainer Fries
RHIC Strategy 2013
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Conversions

Example 1: excess production of particles which are rare in the medium and rare in
the probe sample
jet
photon
dN rare 1 jet
 N
dt

Example: photons
 Need enough yield to outshine other sources of Nrare.


Example 2: chemical equilibration of a rare probe particle
g
s
e.g. g  s  s  g

N rare, excess L

N jet

[RJF, Müller, Srivastava]
[Srivastava, Gale, RJF]
[Zakharov], …..
[Zhang, Vitev]
[Renk]
 s 
w jet  
  5%
 u  d  jet
@ 10 GeV for RHIC
 s 
wce  
 50%

 u  d medium
Example: strangeness at RHIC
 Coupling of jets (not equilibrated) to the equilibrated medium should drive jets towards
chemical equilibrium.


Quark-gluon conversion  proton/pion ratio
Rainer Fries
RHIC Strategy 2013
[W. Liu, RJF, PRC 77 (2008)]
[W. Liu, RJF, PRC 78 (2008)]
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Conclusions

Chemistry: Need identified hadrons up to 8-10 GeV with good statistics.

Diffusion:
out-of-cone energy/momentum in jet measurements
 near-side correlations of hadrons

Rainer Fries
RHIC Strategy 2013
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