quark-gluon plasma physicsreygers/lectures/... · 2019. 10. 3. · j/ψ might form again from...

Quark-Gluon Plasma Physics  10. Quarkonia  

Prof. Dr. Klaus Reygers Heidelberg University SS 2017

QGP physics SS2017 | K. Reygers | 10. Quarkonia

Charmonium and bottomium

■ Non-relativistic treatment for heavy quarks (mc ≈ 1.3 GeV, mb ≈ 4.7 GeV) ■ Charmonium and bottomium states reproduced by  

solving Schrödinger equation using Cornell potential:

2

V (r) = �↵r+ �r

σ ≈1 GeV/fm, α ≈ π/12

Quarkonia: tightly bound, smaller radius than light mesons


Debye screening in the QGP■ Matsui, Satz (Phys. Lett. B 178 (1986)): ‣ Potential between two heavy quarks is modified in the QGP, preventing initially

produced charm anticharm quarks to form a J/ψ ‣ J/ψ suppression is a QGP signal

3

V (r ,T ) = �↵re�µr + �r

1� e�µr

µr

■ Simple parameterization of the screened potential (“Debye screening”)

rD = 1/µscreening radius depends on  temperature:

■ Basic idea: heavy-quark bound state melts in the QGP if

■ There is a dissociation temperate Td for each state  (“sequential melting”):

µ = µ(T ) / g(T )T

Debye mass

Can the different Td’s serve as a QGP thermometer?

arXiv:0706.2183

rQQ̄ & rD


Heavy quark potential for different temperatures from lattice QCD

4

-1

-0.5

0

0.5

1

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1r [fm]

F1(r,T) [MeV]

T=147MeV178MeV194MeV222MeV320MeV442MeV479MeV732MeV

free energy

arXiv:1302.2180v1


Interaction range and J/ψ radius in the medium as a function of the temperature

■ J/ψ radius becomes larger with increasing T ■ No bound state anymore for T ≳ 2 Tc

5

0.5 1.0 1

1.0

0.5

r (T)D [fm]1.5

T/Tc

0

0.5

1

1.5

2

2.5

1 1.2 1.4 1.6 1.8 2 2.2

R[fm

]

T/Tc

J/psi

H. Satz, hep-ph/0512217

Interaction range vs T J/ψ radius vs. T


A new twist: J/ψ might form again from deconfined charm

■ Requires large number of initially produced c cbar pairs: ■ Expect J/ψ suppression at SPS, RHIC and J/ψ enhancement at high

energies (LHC)6

Low (RHIC) energy

Start of collisionDevelopment of

quark–gluon plasma Hadronization

High(LHC) energy

c–c

c–c

D–

D

D–

DD

D–

D–D–

D

D–

D

J/ψ

D

DJ/ψ

NJ/ / N2cc̄

Braun-Munzinger, Stachel, Nature 448 (2007) 302


Expected J/ψ signal with or without statistical recombination of charm quarks

7

J/

Prod

uctio

n Pr

obab

ility

ψ

1

Energy Density

thermal dissociation

statistical recombination

Kluberg, Satz, 0901.3831


Time scales

CERN SPS energies and below:

8

Separation of scales at the LHC (and also RHIC):

Interpretation of the J/ψ signal easier at the LHC (and at RHIC)  as absorption in cold nuclear matter should not be irrelevant

Collision time:

Hadron formation time:

Charm pair formation:

⌧hadron

⇡ 1 fm/c

QGP formation:

⌧cc̄ =1

2mc⇡ 0.08 fm/c

⌧QGP,SPS ⇡ 1 fm/c , ⌧QGP,SPS < 0.5 fm/c , ⌧QGP,LHC < 0.1 fm/c

tcoll

= 2R/�cm (RHIC: 0.1 fm/c ,LHC: 5 · 10�3 fm/c)

tcoll

' ⌧QGP

' ⌧hadron

→ pre-resonant state can be absorbed in cold nuclear matter

absorption of  pre-resonant state in nuclear matter

tcoll

⌧ ⌧QGP

< ⌧hadron


J/ψ suppression at the CERN SPS and at RHIC

■ Same suppression at midrapidity at the CERN SPS and at RHIC, in spite of larger energy density at RHIC

■ RHIC: suppression large at forward rapidity, in spite of larger energy density at mid-rapidity

■ Not easy to explain in pure dissociation picture

9

RAB =dN/dpT |A+B

hTABi ⇥ d�inv/dpT|p+p,

where hTAB

i = hNcoll

i /�NNinel


J/ψ suppression at RHIC and the LHC

10

=0η |η/dchdN

0 200 400 600 800 1000 1200 1400 1600

ψ J

/AAR

0

0.2

0.4

0.6

0.8

1

1.2=2.76 TeVNNs15% syst.), ±ALICE (2.5


J/ψ RAA at the LHC is reproduced by models based on the regeneration mechanism

■ Two different approaches ‣ Statistical hadronization at

the phase boundary ‣ Kinetic recombination of

charm and anti-charm quarks in the QGP (hep-ph/0007323)

■ Important model input: number of initial charm quark pairs

11

partN0 50 100 150 200 250 300 350 400

ψ J

/AAR

0

0.2

0.4

0.6

0.8

1

1.2

1.4 13% syst. uncert.)±ALICE (|y|


)c (GeV/Tp

0 1 2 3 4 5 6 7 8

AAR

0

0.2

0.4

0.6

0.8

1

1.2

1.4 = 0.2 TeVNNs = 2.76 TeV and Au-Au NNsPb-Pb

8%±20% global syst. =


J/ψ seems to flow, too — Support for thermalization of charm quarks in the QGP

13

) c (GeV/Tp

0 1 2 3 4 5 6 7 8 9 10

2v

-0.1

0

0.1

0.2

0.3 < 4.0y = 2.76 TeV), centrality 20%-60%, 2.5 < NNsALICE (Pb-Pb

Y. Liu et al., b thermalized Y. Liu et al., b not thermalized X. Zhao et al., b thermalized

1.4%±global syst. =

ALICE, arXiv:1303.5880v4


Υ at the LHC:  Υ(2s) and Υ(3s) more suppressed in Pb-Pb than Υ(1s)

14

]2) [GeV/c-µ+µMass(

7 8 9 10 11 12 13 14

)2

Eve

nts

/ (

0.1

Ge

V/c

0

100

200

300

400

500

600

700

800

= 2.76 TeVNNsCMS PbPb

Cent. 0-100%, |y| < 2.4

> 4 GeV/cµ

Tp

-1bµ = 150 intL

data

total fit

background

]2) [GeV/c-µ+µMass(7 8 9 10 11 12 13 14

)2Ev

ents

/ ( 0

.1 G

eV/c

0

10

20

30

40

50 = 2.76 TeVsCMS pp

|y| < 2.4 > 4 GeV/cµ

Tp

-1 = 230 nbintL

datatotal fitbackground

CMS, 1208.2826

Qualitatively consistent with sequential melting for the Υ states


Υ at the LHC: RAA vs Npart

15

partN0 50 100 150 200 250 300 350 400

pp(1

S)]

ϒ(2

S)/

ϒ /

[Pb

Pb(1

S)]

ϒ(2

S)/

ϒ[

0

0.2

0.4

0.6

0.8

1

1.2

1.4 = 2.76 TeVNNsCMS PbPb -1bµ = 150 intL

|y| < 2.4 > 4 GeV/cµ

Tp

0-5%

5-10%10-20%

20-30%30-40%

40-50%

50-100%

stat. unc.syst. unc.pp unc.

partN0 50 100 150 200 250 300 350 400

AAR

0

0.2

0.4

0.6

0.8

1

1.2

1.4 = 2.76 TeVNNsCMS PbPb -1bµ = 150 intL

|y| < 2.4 > 4 GeV/cµ

Tp

0-5%5-10%10-20%

20-30%

30-40%

40-50%

50-100%

(1S), stat. unc.ϒ(1S), syst. unc.ϒ(2S), stat. unc.ϒ(2S), syst. unc.ϒ

CMS, arXiv:1208.2826

Υ(1S) appears to be suppressed stronger than one would expect  from the Υ(2S) and Υ(3S) suppression alone (feeddown)


Summary/questions quarkonia

■ Two main effects discussed in A-A collisions ‣ Suppression due to color screening in the QGP ‣ Regeneration of quarkonia for sufficiently large numbers of deconfined c quarks

■ √sNN dependence of J/ψ production consistent with regeneration picture  (at RHIC and, more pronounced, at the LHC) ‣ However, need stronger constraints on initial number of charm quarks from

hard scattering ■ What is the appropriate description of the J/ψ regeneration? ■ Does the melting scenario hold for Y production at the LHC? ■ Can yields of Y states serve as a QGP thermometer?

16

quark-gluon plasma physicsreygers/lectures/... · 2019. 10. 3. · j/ψ might form again from...

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