Heavy-Quark Kineticsin the Quark-Gluon Plasma
Hendrik van Hees
Justus-Liebig Universität Gießen
October 28, 2010
Institut für
Theoretische Physik
JUSTUS-LIEBIG-
UNIVERSITÄT
GIESSEN
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 1 / 18
Outline
1 Heavy-quark interactions in the sQGPHeavy quarks in heavy-ion collisionsHeavy-quark diffusion: The Langevin EquationElastic pQCD heavy-quark scatteringNon-perturbative interactions: Resonance Scattering
2 Non-photonic electrons at RHIC
3 Microscopic model for non-perturbative HQ interactionsStatic heavy-quark potentials from lattice QCDT-matrix approach
4 Summary and Outlook
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 2 / 18
Heavy Quarks in Heavy-Ion collisions
q
K
e±
νe
c,b quark
cg
sQGP
c
q̄
hard production of HQsdescribed by PDF’s + pQCD (PYTHIA)
Hadronization to D,B mesons viaquark coalescence + fragmentationV. Greco, C. M. Ko, R. Rapp, PLB 595, 202 (2004)
HQ rescattering in QGP: Langevin simulationdrag and diffusion coefficients frommicroscopic model for HQ interactions in the sQGP
semileptonic decay ⇒“non-photonic” electron observablesRe
+e−AA (pT ), v
e+e−2 (pT )
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 3 / 18
Relativistic Langevin process
Langevin process: friction force + Gaussian random forcein the (local) rest frame of the heat bath
d~x =~p
Epdt,
d~p = −A~pdt+√
2dt[√B0P⊥ +
√B1P‖]~w
~w: normal-distributed random variableA: friction (drag) coefficientB0,1: diffusion coefficientsdependent on realization of stochastic processto guarantee correct equilibrium limit: Use Hänggi-Klimontovichcalculus, i.e., use B0/1(t, ~p+ d~p)Einstein dissipation-fluctuation relation B0 = B1 = EpTA.to implement flow of the medium
use Lorentz boost to change into local “heat-bath frame”use update rule in heat-bath frameboost back into “lab frame”
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 4 / 18
Elastic pQCD processes
Lowest-order matrix elements [Combridge 79]
Debye-screening mass for t-channel gluon exch. µg = gT , αs = 0.4not sufficient to understand RHIC data on “non-photonic” electrons[Moore, Teaney 2005]Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 5 / 18
Non-perturbative interactions: Resonance Scattering
General idea: Survival of D- and B-meson like resonances above Tcelastic heavy-light-(anti-)quark scattering
q̄
c q̄
c
D,D′, Ds
s
cq
qc
u D,D′, Ds
D- and B-meson like resonances in sQGP
c
q
D,D′, Ds D,D′, Ds
k k
parametersmD = 2 GeV, ΓD = 0.4 . . . 0.75 GeVmB = 5 GeV, ΓB = 0.4 . . . 0.75 GeV
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 6 / 18
Cross sections
1.5 2 2.5 3 3.5 4√s [GeV]
0
2
4
6
8
10
12
σ [
mb
]
Res. s-channelRes. u-channelpQCD qc scatt.
pQCD gc scatt.
total pQCD and resonance cross sections: comparable in size
BUT pQCD forward peaked ↔ resonance isotropicresonance scattering more effective for friction and diffusion
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 7 / 18
Time evolution of the fire ball
Elliptic fire-ball parameterizationfitted to hydrodynamical flow pattern [Kolb ’00]
V (t) = π(z0 + vzt)a(t)b(t), a, b: semi-axes of ellipse,
va,b = v∞[1− exp(−αt)]∓∆v[1− exp(−βt)]
Isentropic expansion: S = const (fixed from Nch)
QGP Equation of state:
s =S
V (t)=
4π2
90T 3(16 + 10.5n∗f ), n
∗f = 2.5
obtain T (t) ⇒ A(t, p), B0(t, p) and B1 = TEAfor semicentral collisions (b = 7 fm): T0 = 340 MeV,QGP lifetime ' 5 fm/c.simulate FP equation as relativistic Langevin process
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 8 / 18
Initial conditions
need initial pT -spectra of charm and bottom quarks
(modified) PYTHIA to describe exp. D meson spectra, assumingδ-function fragmentationexp. non-photonic single-e± spectra: Fix bottom/charm ratio
0 1 2 3 4 5 6 7 8p
T[GeV]
10-7
10-6
10-5
10-4
10-3
10-2
1/(
2 π
pT)
d2N
/dp
T d
y [a
.u.]
STAR D0
STAR prelim. D* (×2.5)
c-quark (mod. PYTHIA)
c-quark (CompHEP)
d+Au √sNN
=200 GeV
0 1 2 3 4 5 6 7 8p
T [GeV]
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
1/(
2π
pT)
dN
/dp
T [
a.u.]
STAR (prel, pp)
STAR (prel, d+Au/7.5)
STAR (pp)
D → e
B → esum
σbb
/σcc
= 4.9 x10-3
e±
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 9 / 18
Spectra and elliptic flow for heavy quarks
0 1 2 3 4 5p
T [GeV]
0
0.5
1
1.5
RA
A
c, reso (Γ=0.4-0.75 GeV) c, pQCD, α
s=0.4
b, reso (Γ=0.4-0.75 GeV)
Au-Au √s=200 GeV (b=7 fm)
0 1 2 3 4 5p
T [GeV]
0
5
10
15
20
v2 [
%]
c, reso (Γ=0.4-0.75 GeV) c, pQCD, α
s=0.4
b, reso (Γ=0.4-0.75 GeV)
Au-Au √s=200 GeV (b=7 fm)
µD = gT , αs = g2/(4π) = 0.4
resonances ⇒ c-quark thermalizationwithout upscaling of cross sections
Fireball parametrization consistent with hydro
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 10 / 18
Comparison to single-electron spectra @ RHIC
AA
R
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
= 200 GeVNNsAu+Au @
0−10% central(a)
Moore &
Teaney (III)T)π3/(2
T)π12/(2
van Hees et al. (II)
Armesto et al. (I)
[GeV/c]T
p0 1 2 3 4 5 6 7 8 9
HF
2v
0
0.05
0.1
0.15
0.2
PRLPHENIX Collaboration
98 172301 (2007)
(b)
minimum bias
> 4 GeV/cT
, pAA R0π
T, p2 v
0π
HF2
v±, eAA
R±e
> 2 GeV/c
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 11 / 18
Microscopic model: Static potentials from lattice QCD
V
Kaczmarek et al
lQCD
color-singlet free energy from latticeuse internal energy
U1(r, T ) = F1(r, T )− T∂F1(r, T )
∂T,
V1(r, T ) = U1(r, T )− U1(r →∞, T )Casimir scaling for other color channels [Nakamura et al 05; Döring et al 07]
V3̄ =1
2V1, V6 = −
1
4V1, V8 = −
1
8V1
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 12 / 18
T-matrix
Brueckner many-body approach for elastic Qq, Qq̄ scattering
T= + VTc
q, q̄V
= Σglu + TΣ
reduction scheme: 4D Bethe-Salpeter → 3D Lipmann-SchwingerS- and P waves
same scheme for light quarks (self consistent!)
Relation to invariant matrix elements∑|M(s)|2 ∝
∑q
da(|Ta,l=0(s)|2 + 3|Ta,l=1(s)|2 cos θcm
)Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 13 / 18
Microscopic justification for resonances: T-matrixcalculation
0
2
4
6
8
10
12
0 1 2 3 4
-Im
T (
GeV
-2)
Ecm (GeV)
s wave
color singlet
T=1.1 TcT=1.2 TcT=1.3 TcT=1.4 TcT=1.5 TcT=1.6 TcT=1.7 TcT=1.8 Tc
0
1
2
3
0 1 2 3 4
-Im
T (
GeV
-2)
Ecm (GeV)
s wave
color triplet
T=1.1 TcT=1.2 TcT=1.3 TcT=1.4 TcT=1.5 TcT=1.6 TcT=1.7 TcT=1.8 Tc
use static heavy-quark potentials from lQCD
resonance formation at lower temperatures T ' Tcmelting of resonances at higher T ! ⇒ sQGPmodel-independent assessment of elastic Qq, Qq̄ scattering
problems: uncertainties in extracting potential from lQCDin-medium potential V vs. F?
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 14 / 18
Transport coefficients
0
0.05
0.1
0.15
0 1 2 3 4 5
Α (
1/f
m)
p (GeV)
T-matrix: 1.1 TcT-matrix: 1.4 TcT-matrix: 1.8 Tc
pQCD: 1.1 TcpQCD: 1.4 TcpQCD: 1.8 Tc
0
10
20
30
40
0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34
2π
T D
s
T (GeV)
pQCD+T-matpQCD
from non-pert. interactions reach Anon−pert ' 1/(7 fm/c) ' 4ApQCDA decreases with higher temperature
higher density (over)compensated by melting of resonances!
spatial diffusion coefficient
Ds =T
mA
increases with temperatureHendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 15 / 18
Non-photonic electrons at RHICsame model for bottomquark coalescence+fragmentation → D/B → e+X
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1 2 3 4 5
RA
A
pT (GeV)
Au-Au √s=200 GeV (central)
pQCD, αs=0.4T-matrix
0
5
10
15
0 1 2 3 4 5
v2 (
%)
pT (GeV)
Au-Au √s=200 GeV
b=7 fm
pQCD, αs=0.4T-matrix 0
0.5
1
1.5
RA
A
theory [Wo]
frag. only [Wo]
theory [SZ]
PHENIX
STAR
0 1 2 3 4 5p
T [GeV]
0
0.05
0.1
0.15
v2
PHENIXPHENIX QM08
0-10% central
minimum bias
Au+Au √s=200 AGeV
coalescence crucial for description of dataincreases both, RAA and v2 ⇔ “momentum kick” from light quarks!“resonance formation” towards Tc ⇒ coalescence natural [Ravagli, Rapp 07]
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 16 / 18
Transport properties of the sQGP
spatial diffusion coefficient: Fokker-Planck ⇒ Ds = TmA = T2
Dmeasure for coupling strength in plasma: η/s
η
s' 1
2TDs (AdS/CFT),
η
s' 1
5TDs (wQGP)
-0.5
0
0.5
1
1.5
2
0.2 0.25 0.3 0.35 0.4
η/s
T (GeV)
charm quarks
T-mat + pQCDreso + pQCDpQCDpQCD run. αsKSS bound
[Lacey, Taranenko (2006)]
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 17 / 18
Summary and Outlook
Summary
Heavy quarks in the sQGPnon-perturbative interactions
mechanism for strong coupling: resonance formation at T & TclQCD potentials parameter freeres. melt at higher temperatures ⇔ consistency betw. RAA and v2!
also provides “natural” mechanism for quark coalescenceresonance-recombination model [L. Ravagli, HvH, R. Rapp, Phys. Rev. C 79, 064902 (2009)]problems
potential approach at finite T : F , V or combination?
Outlook
use more realistic bulk-medium description (real hydro)include inelastic heavy-quark processes (gluo-radiative processes)take into account D/B-meson rescattering in the hadronic phaseother heavy-quark observables like charmoniumsuppression/regeneration
Hendrik van Hees (JLU Gießen) Heavy-Quark Kinetics October 28, 2010 18 / 18
Heavy-quark interactions in the sQGPHeavy quarks in heavy-ion collisionsHeavy-quark diffusion: The Langevin EquationElastic pQCD heavy-quark scatteringNon-perturbative interactions: Resonance Scattering
Non-photonic electrons at RHICMicroscopic model for non-perturbative HQ interactionsStatic heavy-quark potentials from lattice QCDT-matrix approach
Summary and Outlook