quark-gluon plasma physicsreygers/lectures/... · 2019. 10. 3. · j/ψ might form again from...
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Quark-Gluon Plasma Physics 10. Quarkonia
Prof. Dr. Klaus Reygers Heidelberg University SS 2017
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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:
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V (r) = �↵r+ �r
σ ≈1 GeV/fm, α ≈ π/12
Quarkonia: tightly bound, smaller radius than light mesons
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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
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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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
Heavy quark potential for different temperatures from lattice QCD
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-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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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
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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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
Expected J/ψ signal with or without statistical recombination of charm quarks
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J/
Prod
uctio
n Pr
obab
ility
ψ
1
Energy Density
thermal dissociation
statistical recombination
Kluberg, Satz, 0901.3831
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
Time scales
CERN SPS energies and below:
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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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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
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RAB =dN/dpT |A+B
hTABi ⇥ d�inv/dpT|p+p,
where hTAB
i = hNcoll
i /�NNinel
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
J/ψ suppression at RHIC and the LHC
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=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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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
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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|
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
)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. =
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
J/ψ seems to flow, too — Support for thermalization of charm quarks in the QGP
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) 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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
Υ at the LHC: Υ(2s) and Υ(3s) more suppressed in Pb-Pb than Υ(1s)
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]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
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
Υ at the LHC: RAA vs Npart
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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)
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QGP physics SS2017 | K. Reygers | 10. Quarkonia
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?
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