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A common description of jet-quenching and elliptic flowwithin a pQCD transport model
Oliver Fochler
H-QM Graduate Day
18.06.2008
arXiv:0806.1169
Oliver Fochler
A perfect liquid?PRL 92, 052302 (2004)
Universal bound from AdS/CFT?
viscous hydro
ideal hydro
Oliver Fochler
nuclear modification factor
relative to pp (binary collision scaling)
experiments show approx. factor 5 of suppression in hadron yields
Strong jet-quenching
high energy particles as probes of the medium created in AA-collisions
HP 2008, C. Vale
Oliver Fochler
Some jet-quenching schemes BDMPS (Baier, Dokshitzer, Mueller, Peigne, Schiff) GLV (Gyulassy, Levai, Vitev) - opacity expansion
Djordjevic, Wicks, Horowitz, Adil.. ASW (Armesto, Salgado, Wiedemann) - path integral in opacity
Dainese, Loizides, Paic, Eskola, Honkanen, Renk, Ruppert AMY (Arnold, Moore, Yaffe) - finite temp. field theory
Qin, Turbide, Jeon, Gale, Ruppert HT, Higher-Twist (Wang, Guo) - twist power expansion in DIS
Zhang, Zhang, Majumder, Fries, Mueller
Oliver Fochler
Partonic transport model – BAMPS
microscopic transport simulations with full dynamics attack various problems within one model
(thermalization, RAA, jet tomography, v2, initial conditions,...)
BAMPS = Boltzmann Approach to Multiple Particle Scattering, (Z. Xu, C. Greiner, Phys. Rev. C71)
Oliver Fochler
Partonic transport model - BAMPS LO pQCD cross sections calculate transition probabilities for (test)particles
within spatial cells no geometric interpretation of cross sections
simulate gluon plasma including the processes
gg gg gg ggg
V
transition probabilitiesmatrix element integrated overmomentum space
gggg cross section (in small-t (small angle) approximation)
Oliver Fochler
LPM-effect
obtain total cross section for ggggg via integration of the matrix element
possible interference effects cannot be treated in quasi particle picture
incoherent treatment of ggggg processes parent gluon must not scatter during formation time of emitted gluon
discard all possible interference effects (Bethe-Heitler regime)
Gunion-Bertsch matrix element
Oliver Fochler
Reference frames for the LPM cut-off
kt
CM frame
p1 p2
lab frame
kt
= 1 / kt
total boost
integral cuts
‘ << 1 (e.g. thermal particles):
Oliver Fochler
Au+Au – Setup central (b=0 fm) Au-Au collision at 200 AGeV sampling of initial gluon plasma:
initial momentum distribution (mini-jets) according to
Glück-Reya-Vogt parameterization for structure functions; K = 2 lower cut-off: p0 = 1.4 GeV (reproduces dET/dy)
particle production via standard nuclear geometry(Wood-Saxon density profile, Glauber-Model)
each parton is given a formation time 35 testparticles simulate evolution of fireball up to ~5 fm/c when energy density in a cell drops below = 1 GeV
free streaming (in the respective cell)
Oliver Fochler
Thermalization in Au+Au
time evolution of pT spectra
(central region, xT < 1.5 fm, || < 0.5)
Oliver Fochler
Collective flow
inelastic gluon interactions lead to sizeable v2
the shear viscosity can be computed
v2 with fixded cs: cf. Molnar or AMPT
Oliver Fochler
Energy loss in a static medium gluon jet in a static, thermal medium of gluons T = 400 MeV
LPM cut-off increases due to boost
Oliver Fochler
Au-Au – Nuclear modification factor central (b=0 fm) Au-Au collision at 200 AGeV
initial distribution: mini-jets
STAR: PRL 91, 172302 (2003)PHENIX: arxiv:0801.4020 (2008)
Oliver Fochler
Au-Au – Nuclear modification factor central (b=0 fm) Au-Au collision at 200 AGeV
initial distribution: mini-jets
Oliver Fochler
Au-Au – Nuclear modification factor central (b=0 fm) Au-Au collision at 200 AGeV
initial distribution: mini-jets
Oliver Fochler
Fixed binary cross sections?
Only binary collisions with fixed cross section 10 mb clearly overestimate jet-quenching!
Oliver Fochler
Summary and to-do list fully dynamic simulation of jet quenching in central Au+Au collision thermalization, collective flow etc. are investigated in the same
framework
quantitative description of v2 and RAA within a common description
not possible with binary collisions and fixed cross sections
include (light) quarks implement fragmentation scheme crank up computational performance (parallel computing?,
testparticle scheme) look at the observables from the previous slides..
Oliver Fochler
Mean transverse momentum acquired mean transverse momentum squared per collision divided by mean free path T = 400 MeV
Oliver Fochler
Energy loss in a static medium gluon jet in a static, thermal medium of gluons T = 400 MeV