1. Perspectives on Heavy-Flavor + EM Probes with Heavy Ions at LHCb
7/4/2018
Ralf Rapp
Cyclotron Institute +
Dept. of Physics & Astronomy
Texas A&M University
College Station, TX
USA
Workshop on
LHCb Heavy-Ion and Fixed-Target Physics
CERN (Geneva, Switzerland), Jan. 9+10, 2017

2. 1.) Exploring QCD Matter Big Bang Compact Stellar Objects
Bulk Properties: Equation of State, Transport Coefficients
Microscopic Properties: Degrees of Freedom, Spectral Functions
Phase Transitions: Condensate Structure

3. Outline 1.) Introduction 2.) Electromagnetic Probes
7/4/2018
Outline
1.) Introduction
2.) Electromagnetic Probes
• Low- + intermediate-mass dileptons in pA, AA
3.) Heavy Flavor
• pPb: non-/shadowing effects
• Quarkonia in non-central PbPb
• Open charm+bottom diffusion
4.) Summary

4. 2.) EM Spectral Function to Probe Fireball
Thermal Dilepton Rate
Im Πem(M,q;mB,T)
e+e- → hadrons r
Im Pem(M) / M2
Hadronic Resonances
- change in degrees of freedom?
- restoration of chiral symmetry?
Continuum
- temperature?
Low-q0,q limit: transport coefficient (charge)?
Total yields: fireball lifetime?
e+ e-
e e-
M [GeV]

5. 2.2 30 Years of Dileptons in Heavy-Ion Collisions
<Nch>=120
Robust understanding across QCD phase diagram:
QGP + hadronic radiation with melting r resonance

6. 2.3 NA60 Dimuons at SPS (√s=17.3 GeV)
Integrate rates over thermal fireball:
Radiation Spectrum e+ e- r
Low mass:
r-meson melting,
fireball lifetime
High mass:
QGP thermometer
Tavg ~ 200 MeV
q q -

7. 2.4 Melting r and Chiral Restoration
quantitatively compatible with (approach to)
chiral restoration
Chiral r-ɑ1 mass splitting “burns off”,
resonances melt into qq continuum
[Hohler +RR ‘13]

8. 2.5 Wishlist for LHCb Thermal Dileptons
Precision measurement a la NA60 (NB: dNch/dy ~ 120), down to low pT
Low mass:
- Chiral restoration at mB ~ 0
→ direct link to lattice QCD (condensate, conductivity)
- Lifetime measurement of fireball
→ test of hydro/thermalization in peripheral AA
→ Does a fireball form in pA? High-multiplicity pp??
Intermediate-mass continuum
→ early temperatures (thermalization ↔ de-polarization)
→ independent assessment of heavy quarks and their modification

9. 3.) Heavy Quarks: A “Calibrated” QCD Force
[GeV]
V [½ GeV]
r [½ fm]
[Bazavov et al ‘13]
Vacuum quarkonium spectroscopy well described
Confinement ↔ linear part of potential
Objective: Determine medium-modifications of QCD force and
deduce transport properties + spectral functions of
heavy flavor, probing QGP at varying resolution.
Exploit mQ >> LQCD , Tc , TRHIC,LHC

10. 3.2 Quarkonia in Medium In-medium binding energy EB(p,T)
Inelastic reaction rate Gin(p,T,EB)
(dissociation and regeneration)
(1S) : color-Coulomb
J/y, (2S), …: confining force
Non-perturbative effects until ~ 2Tpc
Not a straightforward thermometer…
Need to understand “Cold Nuclear Matter” (CNM) effects (pA?!)

11. 3.3 Heavy Quarks in Medium Q Diffusion: “Brownian motion”
Thermalization delayed by mQ/T
→ memory in URHICs
Direct access to transport coefficient Ds (2πT) (~ η/s ~ sEM/T)
Elastic scattering rates (radiation suppressed, q02<<q2)
→ widths; quasiparticles? (mQT)
Probe of hadronization
Ample connections to lattice QCD Q

12. 3.4 Quarkonia in pA: Hot Matter Suppression?
d-Au(0.2TeV) + p-Pb(5TeV)
Shadowing?
y’ (J/y?) suppression in dAu, pPb
ccbar X-sec pivotal for PbPb

13. 3.5 Bottomonia: (1S) Rapidity Puzzle
problem of large(r) suppression in
2.76 TeV ALICE data
cold nuclear matter effects?
Regeneration: Nbb ~ 1 for central PbPb
 canonical limit NY ~ (Nbb)1

14. 3.6 Heavy-Flavor Transport at RHIC + LHC
flow bump in RAA + large v2 ↔ strong coupling near Tpc (recombination)
v2D,B in non-central AA → precision tool for HF transport coefficient

15. 3.7 Wishlist for LHCb Heavy Flavor
Precision measurements of open+hidden charm + bottom states
Shadowing effects on open HF in pA
→ critical baseline for AA + quarkonia
Non-shadowing effects on quarkonia in pA
→ final-state interactions (“fireball”) in pA? Intrinsic charm?
→ (1S) puzzle in PbPb
v2 of open charm and bottom in non-central AA
→ precision determination of HF diffusion coefficient
Quarkonia in non-central AA
→ clarify strong suppression of (2S) in peripheral coll.
→ measure v2 to clarify role of regeneration for y’, cc +  states

16. 4.) Summary LHCb program for QCD matter studies
PbAr(0.1TeV), PbPb (5TeV)
- Thermal dimuons: Chiral restoration, fireball lifetime, early temperature
- Heavy-flavor diffusion coefficient (v2) in PbAr, PbPb
- excited quarkonia (cc!)
pPb (5TeV)
- Disentangle cold-nuclear matter effects on open + hidden Heavy Flavor
- onfining force screened at RHIC+LHC, regeneration of J/y (y’ ?)
- Color screening of (1S)? Role of regeneration? …

17. 3.2 Heavy-Flavor Transport in URHICs
| | | |
t [fm/c] D c
initial cond.
(nPDFs, …),
pre-equil. fields
c-quark diffusion
in QGP liquid
c-quark
hadronization
D-meson
diffusion in
hadron liquid
no “discontinuities” in interaction
 diffusion toward Tpc and hadronization same interaction (confining!)
[Moore+Teaney ‘05, van Hees et al ‘05, Gossiaux et al ‘08, Vitev et al ‘08, Das et al ‘09, Uphoff et al ’10,
M.He et al ‘11, Beraudo et al ‘11, Cao et al ’13, Bratkovskaya et al ‘14, …]

18. 4.1 Upshot of Quarkonium Phenomenology
A. Charmonia (J/y)
SPS: large cold-nucl.-abs., RAAhot ~ 0.8
RHIC: RAAhot ~ 0.6
LHC: RAAhot ~ 0.7,
low-pT excess, sizable v2
B. Bottomonia
RHIC: RAA[(1S)] ~ 0.7
LHC: RAA[(1S)]~0.4, RAA[(2S)]~0.1
C. Implications
- T0SPS (~230) < Tdiss(J/y,’) < T0RHIC (~350) < T0LHC(~550) ≤ Tdiss()
- confining force screened at RHIC+LHC
- thermalizing(!) charm quarks recombine at LHC

19. 2.4 Parton Spectral Functions in QGP
Up/Down + Gluon Charm Bottom
QGP structure changes with resolution scale
Quasi-particles re-emerge when
increasing Mq, p, T

20. 2.3 D-meson + c-Quark Spectral Functions in QGP
T-matrix w/ “lattice potential” V In-Medium c-Quark Selfenergy
q,g SQ Q =
D-meson resonances near Tpc → c-quark quasi-particles at high T

21. 4.4  Regeneration and Elliptic Flow
Sizeable effect only for (2S)

22. 4.5  Binding Energies

23. 3.6 Charm Transport at LHC: D-Meson Spectra
[M.He et al ’14]
RAA “bump” from radial flow
Ds meson (cs) enhanced from coalescence with strange quarks
Coalescence + hadronic diffusion increase v2
similar features at RHIC

24. 4.2 Charmonia in d+Au Fireball
construct fireball + evolve rate equat.
→ y suppression from hot medium
similar in spirit to comover approach
formation time effects?!
[Ferreiro ‘14]
[X.Du+RR, in prep]
[Y.Liu, Ko et al ‘14]

25. 3.6 (1S) and (2S) at LHC Weak Binding Strong Binding (1S) → (2S)
[Grandchamp et al ’06,
Emerick et al ‘11]
sensitive to color-screening + early evolution times
clear preference for strong binding (U potential)
similar results by
possible problem in rapidity dependence
[Strickland ‘12]