open charm at lhc · 200 300 400 500 dn/dp t=0 fm t=2 fm t=4 fm t=6 fm charm 2 4 6 8 10 12 14 p...

Open Charm at LHCMarlene Nahrgang

Duke University

July 8th, Dubna,Strangeness in Quark Matter

2015

1 / 34

Probes of the quark-gluon plasma• Study of properties of strongly interacting many-body systems via ultra-relativistic

heavy-ion collisions.

• Probes should not thermalize with the medium, e.g. dileptons, high-pT jets,...

• The mass of heavy quarks (HQ) sets another scale: mc , mb

• HQ vacuum shower terminates much earlier: E/Q2H with QH =

√Q2

0 + m2Q .

• Number of thermally excited HQ is negligibly small.

• Contributions from gluon-splitting are negligible for charm quarks at currentpT -range.

• HQ as leading parton is always tagged.

2 / 34

Quark-gluon plasma and its properties

jet quenching

observable: nuclear modification factor

RAA(pT ) =1

Ncoll

dNAA/dpT

dNpp/dpT

sensitive to jet quenching parameter q

collective flow

observable: Fourier coefficients of

d2NdpT dy

∝ ∑n

vn cos(nφ)

sensitive to viscosity η/s

3 / 34

Formation of QGP, which evolves fluid dynamically as a nearly perfect fluid.


jet quenching

Jet Collab. PRC90 (2014)


RAA(pT ) =1

Ncoll

dNAA/dpT

dNpp/dpT


collective flow

0

0.1

0.2

0.3

0.4

0.5

0 0.5 1 1.5 2 2.5 3 3.5 4

v2

pT [GeV]

LHC 2.76 TeV

ALICE h+/-

30-40%

ideal, avg

η/s=0.08, avg

ideal, e-b-e

η/s=0.08, e-b-e

η/s=0.16 , e-b-e

B. Schenke et al. PLB702 (2011)


d2NdpT dy

∝ ∑n

vn cos(nφ)


4 / 34



jet quenching

Jet Collab. PRC90 (2014)


RAA(pT ) =1

Ncoll

dNAA/dpT

dNpp/dpT


collective flow

0

0.1

0.2

0.3

0.4

0.5

0 0.5 1 1.5 2 2.5 3 3.5 4

v2

pT [GeV]

LHC 2.76 TeV

ALICE h+/-

30-40%

ideal, avg

η/s=0.08, avg

ideal, e-b-e

η/s=0.08, e-b-e

η/s=0.16 , e-b-e

B. Schenke et al. PLB702 (2011)


d2NdpT dy

∝ ∑n

vn cos(nφ)


5 / 34


Learn from the success in the light hadron sector for heavy-flavor studies!

What to expect from heavy-quark observables?

PHENIX, PRC84 (2011)

at low pT ∼ mQ

• Very different from light partons.

• Nonperturbative!

• Partial thermalization with the lightpartons in the QGP?

• Diffusion D mainly via collisionalprocesses?

• Hadronization viacoalescence/recombination?

• Initial shadowing and cold nuclearmatter effects?

at high pT >> mQ

• Similar to light partons.

• Perturbative regime...

• Rare processes, probe the opacity ofthe matter.

• Energy loss dE/dx via collisional andradiative processes?

• Coherent energy loss→jet-quenching parameter q?

• Hadronization via (medium-modified)fragmentation?

6 / 34

Modeling of heavy-quark dynamics in the QGP

103

104

105

106

107

108

0 5 10 15 20 25 30

dσ

/dp

t (p

b/G

eV

)pt [GeV]

pp Õ D+ + X

LHC 7 TeV

|y| < 0.5CTEQ6.6

FONLL [f(c Õ D+) = 0.238]

POWHEG-PY

POWHEG-HW

MC@NLO

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

ratio

to

FO

NL

L

pt [GeV]

W. Ke et al., Duke, in prep.

• LO pQCD, e.g. FONLL→ inclusive spectra, no azimuthal QQ correlationsM. Cacciari et al. PRL95 (2005), JHEP 1210 (2012)

• NLO pQCD matrix elements plus parton shower, e.g. POWHEG or MC@NLO⇒exclusive spectra, like QQ correlations S. Frixione et al. JHEP 0206 (2002), JHEP 0308 (2003)

• Consistent initialization of HF and LF sectors!

• Cold nuclear matter effects, i.e. shadowing, pT broadening aka Cronin effect, etc.K. J. Eskola, H. Paukkunen and C. A. Salgado, JHEP 0904 (2009)

7 / 34

production interaction with the medium hadronization

Remember talk by C.Y. Wong Tue 15h40!


103

104

105

106

107

108

0 5 10 15 20 25 30

dσ

/dp

t (p

b/G

eV

)pt [GeV]

pp Õ D+ + X

LHC 7 TeV

|y| < 0.5CTEQ6.6

FONLL [f(c Õ D+) = 0.238]

POWHEG-PY

POWHEG-HW

MC@NLO

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

ratio

to

FO

NL

L

pt [GeV]

W. Ke et al., Duke, in prep.

• LO pQCD, e.g. FONLL→ inclusive spectra, no azimuthal QQ correlationsM. Cacciari et al. PRL95 (2005), JHEP 1210 (2012)

• NLO pQCD matrix elements plus parton shower, e.g. POWHEG or MC@NLO⇒exclusive spectra, like QQ correlations S. Frixione et al. JHEP 0206 (2002), JHEP 0308 (2003)

• Consistent initialization of HF and LF sectors!

• Cold nuclear matter effects, i.e. shadowing, pT broadening aka Cronin effect, etc.K. J. Eskola, H. Paukkunen and C. A. Salgado, JHEP 0904 (2009)

8 / 34


Remember talk by C.Y. Wong Tue 15h40!

∆φ DD distributions in pp collisions need to be betterunderstood!


J. D. Bjorken (1982); E. Braaten et al, PRD 44 (1991), PRD 44 (1991); A. Peshier, PRL 97 (2006); S. Peigne et al., PRD 77 (2008) 114017;

M. Gyulassy et al, NPB 420 (1994); BDMPS PLB 345 (1995); NPB 483 (1997); ibid. 484 (1997); B. G. Zakharov, JETP Lett. 63 (1996) 952;

ibid. 64 (1996) 781; ibid. 65 (1997) 615; ibid. 73 (2001) 49; ibid. 78 (2003) 759; M. Gyulassy et al, PRL 85 (2000); NPB 571 (2000) 197;

ibid. 594 (2001); Y. L. Dokshitzer et al., PLB 519 (2001); P. B. Arnold et al., JHEP 0011 (2000), 0305 (2003); N. Armesto et al., PRD

69(2004); PRCC 72 (2005); B.-W. Zhang et al., PRL 93 (2004); NPA783 (2007); S. Wicks et al., NPA783 (2007); W. Horowitz et al., PLB666

(2008); P. Chesler et al. JHEP1310 (2013); B. Kampfer et al., PLB 477 (2000); M. Djordjevic et al., PRC 68 (2003); PLB560 (2003); NPA733

(2004); PRC 77 (2008); PLB734 (2014); M. Bluhm et al. PRL 107 (2011); O. Fochler et al. PRD88 (2013); J. Aichelin et al. PRD89 (2014),

A. Majumder 1506.08648

9 / 34


Remember talk by B. Blagojevic Tue 17h40!


S. Cao et al. arxiv:1505.01413Gossiaux et al. PRC 78 (2008)

• Coalescence/Recombination – predominantly at small pT . Parameter-dependent!e.g. C. B. Dover et al., PRC 44 (1991)

• Fragmentation – predominantly at large pT . Medium-modification?e.g. M. Cacciari et al., PRL 95 (2005)

• After hadronization: final hadronic interactions of D mesons.L. Tolos et al., PRD88 (2013); J. Torres-Rincon et al., PRD89 (2014)

10 / 34


See talk J. Torres-Rincon Thu 17h40!

Set the stage: Transport equations & coefficients

Boltzmann equation for HQ phase-space distribution

ddt

fQ(t ,~x ,~p) = C[fQ ] with C[fQ ] =∫

d~k [w(~p +~k ,~k)fQ(~p +~k)︸︷︷︸gain term

−w(~p,~k)fQ(~p)︸︷︷︸loss term

]

expanding C for small momentum transfer k p (in the medium k ∼ O(gT )) andkeeping lowest 2 terms⇒ Fokker-Planck equation

∂

∂tfQ(t ,~p) =

∂

∂pi

(Ai (~p)fQ(t ,~p) +

∂

∂pj

[Bij (~p)fQ(t ,~p)

])friction (drag) momentum diffusion

Recast to Langevin equation (probably good for bottom, but for charm?)

ddt~p = −ηD(p)~p +~ξ with 〈ξ i (t)ξ j (t ′)〉 = κδij δ(t − t ′)

Transport coefficients connected by fluctuation-dissipation theorem (Einstein relation):

ηD =κ

2mQT, Ds =

TmQηD

spatial diffusion

D. Walton et al., PRL84 (2000); G. Moore et al., PRC71 (2005)

11 / 34

Boltzmann vs Langevin dynamics

• Under which conditions should Brownian motion be a valid approximation forrelativistic particles?

• Calculations of transport coefficients from the underlying theory do notnecessarily fulfil FDT.

• Langevin leads to Gaussian momentum distribution, Boltzmann very different.

Langevin Boltzmann

0 2 4 6 8 10 12 14

p [GeV]

0

100

200

300

400

500

dN/dp

t=0 fm

t=2 fm

t=4 fm

t=6 fm

Charm

2 4 6 8 10 12 14p [GeV]

100

200

300

400

500

dN

/dp

t=0 fmt=2 fmt=4 fmt=6 fm

Charm

S. Das et al, PRC90 (2014)

12 / 34

Remember talk by S. Das Tue 16h20!

Boltzmann equation assumes independent scatterings (dilute medium) - isthis a correct assumption?

Diffusion coefficient from lattice QCD

Lattice QCD at finite T is performed in Euclidean space⇒ notoriously difficult tocalculate dynamical quantities.

Transport coefficients calculated from correlation function of conserved currents

via slope of spectral function ρE at ω = 0 (Kubo formula)

momentum diffusion:

κ

T 3 = limω→0

2T ρE (ω)

ω

spatial diffusion: Ds = 2T 2

κ

1 1.5 2 2.5 3

T/T

0

4

8

12

16

2π

T D

Ding et al. (2012)

Banerjee et al. (2012)

Kaczmarek (2014)

s

c

13 / 34

No reliable input from lattice QCD calculations yet...

Collisional (elastic) energy loss

LO Feynmann diagrams for perturbative heavy quark scattering off a light parton

Q Q

gg

Q Q

gg q q

Q Q

g

QQ

g

• t-channel IR singularity, regulated by the Debye screening mass mD

• HTL energy loss: resummed propagator for |t | t∗, bare propagator |t | t∗

• Relevant separation of scales g2T 2 T 2 probably not fullfilled at RHIC/LHC.

• One-gluon exchange model: reducedIR regulator λm2

D in the hardpropagator

• Running coupling αeff(t) andself-consistentm2

D = (1 + 6nf )4παs(m2D)T

2

A. Peshier, hep-ph/0601119, PRL 97 (2006); P. B. Gossiaux et al. PRC78 (2008), NPA 830 (2009)

14 / 34

Radiative energy loss

q

p2

p1

p4

p3

k

q

p2

p1

p4

p3

k

q

p2

p1

k

p4

p3

q

p2

p1

k

p4

p3

q

q − k

p2

p1

p4

k

p3

• Extention of Gunion-Bertsch approximation beyond mid-rapidity and to finitemass mQ (heavy quarks!) ⇒ distribution of induced gluon radiation (E loss

rad ∝ E L):

Pg(x , ~k⊥, ~q⊥,mQ) =3αs

π21− x

x

~k⊥~k⊥

2+ x2m2

Q

−~k⊥ − ~q⊥

( ~k⊥ − ~q⊥)2 + x2m2Q

2

J. Gunion, PRD25 (1982); O. Fochler et al. PRD88 (2013); J. Aichelin et al. PRD89 (2014)

τform

lmfp

• coherent (LPM) emission if τform =√

ωq > lmfp

• E lossrad ∝

√E L, if τform > L then E loss

rad ∝ L2

• Dynamical realization challengingK. Zapp et al. PRL103 (2009), JHEP 1107 (2011)

• Dead cone effect: Dokshitzer et al., PLB 519 (2001)

dσrad

θdθ∝

θ2(θ2 + M2

Q/E2Q

)• When the hard scattering assumption is relaxed,

emission at low k⊥ is significantly less suppressed.J. Aichelin et al. PRD89 (2014)

15 / 34

Non-perturbative approaches

Resonance scattering:

• Basic assumption: for T . 3Tc two-bodyinteractions→ potential V (t)

• Spatial diffusion coefficient comparable toquenched lQCD.

• smooth transition to hadronic medium withminimum close to Tc

H. v. Hees, PRC73 (2006); H. v. Hees, PRL100 (2008); R. Rapp arxiv:0903.1096

Strong coupling:

• In AdS/CFT a heavy quark is represented by a string connected to a D7 brane.

• Leading-order drag coefficients were excluded by comparison to data.

• Momentum-kicks are multiplicative and grow with the HQ velocity→ importanttoward higher pT !

• At larger momenta HQ in strong-coupling reach a speed limit→ expected to workin an intermediate pT regime! W. Horowitz, PRD (2015)

16 / 34

See talk by W. Horowitz, Fr 16h!

From theoretical input to dynamical modeling

τform

lmfp

)c (GeV/T

p0 2 4 6 8 10 12 14 16

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

WHDG rad+collPOWLANGCao, Qin, BassMC@sHQ+EPOS, Coll+Rad(LPM)BAMPSTAMU elasticUrQMD

|<0.5y average, |*+

, D+

, D0

ALICE D

= 2.76 TeVNNsPbPb,

Centrality 020%

• Simple approximations are prone to fail in some kinematic region, mostly atintermediate pT .

• Due to uncertainties all models when compared to data contain (implicit orexplicit) parameter tuning.

• Proper modeling of the QGP evolution is important! Should be well tested in thelight hadron sector!

• Does the equation of state match the representation of the mediumquasiparticles?

• Effects of viscosity, initial state fluctations, preequilibirum dynamics?

17 / 34

How to get access to fundamental QGP properties from theory to datacomparison?

D meson RAA and v2 in AA at LHCpu

rely

elas

ticsc

atte

rings

(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

= 2.76 TeVNNsPbPb at

Centrality: 0-20%

ALICE D mesons (|y|<0.5)TAMUPOWLANG (HTL) vac.frag.POWLANG (HTL)MC@sHQ+EPOS2BAMPS el.UrQMD

(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

2v

0.1−

0

0.1

0.2

0.3

0.4

0.5

0.6


Centrality: 30-50%


(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8


Centrality: 0-20%

ALICE D mesons (|y|<0.5)

WHDG

MC@sHQ+EPOS2+rad.+LPM

BAMPS rad.+el.

Vitev et al.

Djordjevic et al.

Duke

(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

2v

0.1−

0

0.1

0.2

0.3

0.4

0.5

0.6


Centrality: 30-50%


WHDG


BAMPS rad.+el.

Duke

elas

ticsc

atte

rings

+ra

diat

ion

SaporeGravis Network, arXiv:1506.03981

• The simultaneous description of RAA and v2 is challenging.

18 / 34

D meson RAA and v2 in AA at LHCpu

rely

elas

ticsc

atte

rings

(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8


Centrality: 0-20%


(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

2v

0.1−

0

0.1

0.2

0.3

0.4

0.5

0.6


Centrality: 30-50%


(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

AA

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8


Centrality: 0-20%


WHDG


BAMPS rad.+el.

Vitev et al.

Djordjevic et al.

Duke

(GeV/c)T

p0 2 4 6 8 10 12 14 16 18 20

2v

0.1−

0

0.1

0.2

0.3

0.4

0.5

0.6


Centrality: 30-50%


WHDG


BAMPS rad.+el.

Duke

elas

ticsc

atte

rings

+ra

diat

ion

SaporeGravis Network, arXiv:1506.03981

• The simultaneous description of RAA and v2 is challenging.

19 / 34

(Too?) many models reproduce the RAA and/or the v2 well.

D meson RAA and v2 - miscellaneous

plot by S. Das, Catania

• Enhancement of strangeness in theQGP can lead to an enhancement ofDs mesons by coalescence.

• RAA robust, but v2 changessignificantly:

• affected by interaction details,Langevin vs Boltzmann, coalescence,hadronic final interactions...

0 5 10 15 200.0

0.5

1.0

1.5

2.0

Pb + Pb, sNN= 2.76 TeV, 0-7.5% ALICE (prel.), average D meson ALICE (prel.), Ds meson

D meson at Tkin Ds meson at Tc

RA

A

pT (GeV)

H. Min et al. PLB735 (2014)

20 / 34

Charm production (and diffusion?) in pPb collisions

• 3 + 1d fluid dynamical evolution + Langevin dynamics, initial shadowing.

• Centrality dependence of RpPb expected due to energy loss.(Note, that experimentally QpPb !)

• Indications that v2 of D mesons decouples from medium flow - unlike in AAcollisions - and decreases with centrality.

• Can HF measurements in pPb help answering the question of initial vs final stateeffects?

Y. Xu et al, Duke University, in preparation

21 / 34

Beyond traditional observables...

• Observables with high discriminating power between different interactionmechanisms: e.g. azimuthal correlations of QQ pairs.

〈p⊥〉 from MC@sHQ+EPOS2:

T = 400 MeV

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20 25

d〈p

2 ⊥〉/dt[G

eV2/fm

]

pini|| [GeV]

coll, K = 1.5rad, K = 1.8

coll+rad, K = 0.8

DD correlation plot from Duke model

-π/2 0 π/2 π 3π/2∆φ

0.150

0.155

0.160

0.165

0.170

0.175

1/N

dN

/d∆

φ

col.+rad. D(2πT)=5.0col. only D(2πT)=1.5

rad. only D(2πT)=3.0

col. only without flow

Au-Au @ 200 GeV 0-10%

D-Dbar correlation

PYTHIA initialization

pT, trig

> 2 GeV

(a)

MN et al. PRC90 (2014) Cao et al., arxiv:1505.01869

• Difficulties: already the cc proton-proton baseline is not well understoodtheoretically and experimental feasibility...

22 / 34

For possible e(HF)-h or D-h correlations models need to couple HF-LF sectorsconsistently!

Beyond traditional observables...

• Most models give a τrelax for charm quarks much longer than the evolution of theQGP, but v2(HF) ∼ v2(LF).

• Higher-order Fourier coefficients were important for understanding chargedhadron flow.

• What about heavy-flavor v3, v4, ...?

0

0.05

0.1

0.15

0 2 4 6

vn

pT [GeV]

LHC, 20−30%

D mesons

v2

v3

v4

v5 0.01

0.1

1

0 10 20 30 40 50

vn/ε

n

centrality [%]

v2/ε2

light charged hadronsD mesonsB mesons

0 10 20 30 40 50 60

centrality [%]

v3/ε3

• Expectation: v3 and higher-order coefficients show the incomplete coupling ofHQ to the medium.

MN et al. PRC91 (2015)

23 / 34

Looking forward to experimental data for v3 from LHC and RHIC!

Summary

QQ

• HQ probe partial thermalization at low pT and energy loss athigh pT in the QGP.

• Many effects important at intermediate pT : onset of coherentgluon emission, gluon thermal mass, finite path length,nonperturbative scatterings,...

• Transport coefficients/scattering cross sections in Langevin orBoltzmann transport.

• Coupling to a dynamical evolution of the QGP (should be welltested in the light hadron sector!)

• RAA and v2 are described well by (too?) many models.

• Learn from the success in the the light-flavor sector!

• Study further observables, like QQ correlations andhigher-order flow coefficients, for veri/falsi-fication of models!

• Need to identify most dominant features of HQ-mediuminteraction: connect data to fundamental properties of QCD!

Thanks to J. Aichelin, S. Bass, S. Cao, P.B. Gossiaux, K. Werner, Y. Xu for fruitfulcollaborations and discussions!

24 / 34

Don’t miss plenary talks (theory) by M. Djordjevic, A. Beraudo, this session,E. Bratkovskaya Thu 12h30!

backup

25 / 34


• Model the QGP: a locally thermalized medium provides the scattering partners.

• Input from a fluid dynamical description of the bulk QGP medium: temperaturesand fluid velocities.

• Use a fluid dynamical description which describes well the bulk observables!

smooth initial conditions

-8 -6 -4 -2 0 2 4 6 8

-8

-6

-4

-2

0

2

4

6

8

0

5

10

15

20

25

30

35

40

45

energ

y d

ensity in G

eV

/fm

3

fluctuating initial conditions

-8 -6 -4 -2 0 2 4 6 8

-8

-6

-4

-2

0

2

4

6

8

0

5

10

15

20

25

30

35

40

45

energ

y d

ensity in G

eV

/fm

3

0 5 1 0 1 50 . 00 . 20 . 40 . 60 . 81 . 01 . 21 . 4

y = 0

D - m e s o n s

0 - 2 0 %

A L I C E , 0 - 2 0 % E v e n t - b y - e v e n t : r a d + c o l l ( K = 0 . 8 ) c o l l ( K = 1 . 5 ) A v e r a g e d : r a d + c o l l ( K = 0 . 8 ) c o l l ( K = 1 . 5 )

R AA

p T [ G e V ]

plot by V. Ozvenchuk, Nantes

MN, J. Aichelin, P. B. Gossiaux, K. Werner NPA932 (2014)

26 / 34


medium description coupling medium - HF sector

“Partonic wind” effect

X. Zhu, N. Xu and P. Zhuang, PRL 100 (2008)

• Due to the radial flow of the matterlow-pT cc-pairs are pushed into thesame direction.

• Initial correlations at ∆φ ∼ π arewashed out but additional correlationsat small opening angles appear.

• This happens only in the purelycollisional interaction mechanism!

• No “partonic wind” effect observed incollisional+radiative(+LPM)interaction mechanism!

~p iniT,Q

~p iniT,Q

~p finT,Q

~p finT,Q

~p finT,cm

flow

cc, 0− 20%

LHC 1 < pT/GeV < 4

dN

cc/d∆φ

∆φ

0

0.05

0.1

0.15

0.2

0.25

0 1 2 3 4 5 6

coll, K = 1.5coll+rad, K = 0.8


27 / 34

QGP: initial state and bulk flow (2)

0

0.1

0.2

0.3

0.4

0.5

0.6

εn

LHC

ε2 ε3

0

0.1

0.2

0.3

0.4

0.5

0−10 10−20 20−30 30−40 40−50 50−60

εn

centrality [%]

RHIC

average temperature and overlap area

0.2

0.3

0.4

0.5

0.6

0−10 10−20 20−30 30−40 40−50 50−60

<T

ini>

[G

eV

]

centrality [%]

LHC

0

50

100

150

200

250

0−10 10−20 20−30 30−40 40−50 50−60

<A

ini>

[fm

2]

centrality [%]

LHC

centrality dependence:

+ increase of initial eccentricities

+ decrease of interaction rate and medium size

⇒ expectation: heavy-flavor flow shows a weakerdependence on centrality, especially for v3


28 / 34

D meson v2 and v3 at LHC and RHIC

0

0.1

0.2

0.3

2 4 6 8 10 12

vn

pT [GeV]

0−10%

v2v3

2 4 6 8 10 12

pT [GeV]

10−30%

coll, K=1.5

coll+rad, K=0.8

2 4 6 8 10 12

pT [GeV]

30−50%

v2 ALICE D

0

0.1

0.2

0 1 2 3 4 5

vn

pT [GeV]

0−10%

v2v3

1 2 3 4 5

pT [GeV]

10−20%

coll, K=1.8

coll+rad, K=1.0

1 2 3 4 5

pT [GeV]

RHIC D

20−40%

• At small pT : relative enhancement of flow in purely collisional scenario overcollisional+radiative(+LPM) larger for v3 than for v2


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Charm flow: hadronization and energy loss

collisional+radiative(+LPM), K = 0.8

0

0.1

0.2

0 2 4 6 8 10

vn

pT [GeV]

LHC, 30−50%

D mesons

charm quarks

v2

v3

0

0.1

0.2

0 2 4 6 8 10

vn

pT [GeV]

LHC, 30−50%

charm quarks

w bulk flow

w/o bulk flow

v2

v3

• Contribution to the flow from hadronization.

• For low pT the charm flow is predominantly due to the flow of the bulk.


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Radiative energy loss

I Incoherent radiation:Gunion-Bertsch spectrumextended to finite quark mass.J. Aichelin et al., PRD89 (2014), arXiv:1307.5270

I Inclusion of an effectivesuppression of the spectra in thecoherent radiation regime (LPMeffect)

I Influence of gluon damping (not inthis talk)M. Bluhm et al., PRL 107 (2011), arXiv:1204.2469

T=250 MeV, E=20GeV

c-quark

GB

LPM

1.000.50 5.000.10 10.000.05Ω@GeVD

0.2

0.4

0.6

0.8

1.0

1.2

1.4

d I

dzdΩ

T=250 MeV, E=20GeV

b-quark

GB

LPM

1.000.50 5.000.10 10.000.05Ω@GeVD

0.2

0.4

0.6

0.8

1.0

1.2

1.4

d I

dzdΩ

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pQCD Boltzmann transport• pQCD-inspired Boltzmann transport in 3 + 1d ideal fluid dynamics (EPOS) or in

partonic transport (BAMPS).

MN et al. (Nantes) - MC@sHQ+EPOS2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25 30

RA

A

pT [GeV]

ALICE D, 0−7.5%

dashed lines are with EPS09 shadowing

coll, K=1.5

coll+rad, K=0.8

0

0.05

0.1

0.15

0.2

0.25

0.3

0 2 4 6 8 10 12 14

v2

pT [GeV]

ALICE D, 30−50%

coll, K=1.5

coll+rad, K=0.8

Uphoff et al. (BAMPS)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25 30 35

D m

eson R

AA

pT [GeV]

Pb+Pb, √s = 2.76 TeV

b = 3.6 fm, |y| < 0.5

running αs

κ=1.0, XLPM=1.0 κ=0.2, XLPM=0.2

only 2→2, κ=0.2, K=3.50-7.5% (ALICE)

0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10 12 14 16

D m

eson v

2

pT [GeV]

Pb+Pb√s = 2.76 TeV

b = 9.7 fm

|y| < 0.5

running αs

κ=1.0, XLPM=1.0κ=0.2, XLPM=0.2

only 2→2, κ=0.2, K=3.530-50% (ALICE)

• Rather good description of the RAA and the v2.

• Slight preference for purely collisional energy loss in MC@sHQ+EPOS2.

MN et al. PRC 89 (2014); K. Werner et al. PRC 85 (2012); J. Uphoff et al. arxiv:1408.2964 (2014)

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Importance of recombination - RHIC

• Recombination needs to be included in order to describe the RAA at lower pT .

Cao et al. arxiv:1505.01413

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Non-perturbative resonance scattering

• Basic assumption: two-body interactions→ potential V (t) with t ' −~q 2 (c, bquarks; T . 3Tc )

• T -matrix follows from Lippmann-Schwingerequation: T = V +

∫d3kV G2 T → HQ transport

coefficients, e.g. AQ(~p) ∼ |T |2

• Medium-modified HQ potential from lQCDfree/internal energy:

I Stronger interaction from internal energybased V

I Enhanced ∆Eloss than in pQCD due toresonant HQ-meson and di-quark states inscattering channels

• Spatial diffusion coefficient Ds = 2πT 2/mQAQ :I comparable to quenched lQCDI smooth transition to hadronic medium with

minimum close to Tc

H. v. Hees, PRC73 (2006); H. v. Hees, PRL100 (2008); R. Rapp arxiv:0903.1096

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open charm at lhc · 200 300 400 500 dn/dp t=0 fm t=2 fm t=4 fm t=6 fm charm 2 4 6 8 10 12 14 p...

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