A common description of jet-quenching and elliptic flowwithin a pQCD transport model

Oliver Fochler

H-QM Graduate Day18.06.2008

arXiv:0806.1169

Oliver Fochler

present

(near) future

Oliver Fochler

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-quenchinghigh 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

Are we there yet?Well, not quite. Some things to look at..

HP 2008, C. Vale

Oliver Fochler

More things to look at..

Oliver Fochler

And more..In-Plane

Out-of-Plane

Oliver Fochler

And even more..

3 < pt,trig< 4 GeV/c 4 < pt,trig < 6 GeV/c

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

Thank you!

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

Oliver Fochler

Gluon-Quark-Ratio

Oliver Fochler

Au-Au – Reconstruction partons with high-pt too rare simulate large number of initial conditions select events according to highest pt-(test)particle simulate only selected events and weight results

full: 200000 events; reconstruction: 40 events per pt-bin, ~1000 total