1. Heavy Ion Theory Review
Raju Venugopalan
Brookhaven National Laboratory
LHC week in Split, October 1-6, 2012

2. Heavy Ion Theory (Selective) Review
Raju Venugopalan
Brookhaven National Laboratory
LHC week in Split, October 1-6, 2012

3. Some key questions in heavy ion physics
How is entropy produced and what is the nature of the matter produced ?
How does strongly correlated matter evolve ?
How do hard probes (jets, Onia,…) interact with the matter ?
What can we learn about how emergent features (topological, chiral) of QCD with varying T, μB and B ?

4. Some key questions in heavy ion physics
How is entropy produced and what is the nature of the matter produced ?
How does strongly correlated matter evolve ?
How do hard probes (jets, Onia,…) interact with the matter ?
What can we learn about how emergent features (topological, chiral) of QCD with varying T, μB and B ?
Close analogies to key issues in strongly correlated electron systems, Bose-Einstein
condensates, early universe cosmology (inflation and hot era), plasma physics,
chaotic dynamical systems, classical and quantum gravity

5. Multi-particle production: saturated wave-functions
Incoming nuclei are Color Glass Condensates: Highly occupied gluon states with maximal occupancy allowed in QCD

6. Multi-particle production: saturated wave-functions
Dumitru,Jalilian-Marian,Lappi,Schenke,RV, PLB706 (2011)219
Energy evolution of multi-gluon correlators (on sat. scale ~ 1/QS ) test fundamental features of QCD in deeply non-linear regime

7. Gluon saturation and CGC: Strong hints
i) Good agreement of saturation models with
combined HERA data for x < 0.01
ii) Hadron correlations in deuteron-gold collisions at RHIC
iii) Bulk features of LHC pp data
iv) CMS “ridge” – di-hadron correlations in high multiplicity p+p
Upcoming p+Pb at 5 TeV: possibly stringent tests
from multiple final states

8. Gluon saturation and CGC: Strong hints
Theory:Tribedy, RV,
Theory: Albacete et al
HERA e+p
cross-sections
p+p
Theory: Stasto,Xiao,Yuan,
Theory: Dusling, RV,
d-Au di-hadron to p+p ratio
PHENIX, PRL107,
(2011)
CMS p+p ridge

9. Gluon saturation and CGC: p+Pb constraints
Albacete,Dumitru,Fujii,Nara,

10. The Glasma
Glasma (\Glaahs-maa\): Noun: non-equilibrium matter between CGC and QGP
Solutions of Yang-Mills equations produce (nearly) boost invariant gluon field configurations: “Glasma flux tubes”
Lumpy gluon fields color screened over transverse distances ~ 1/QS
- Convolution of NBD multiplicity distributions.
Glue configurations very unstable to
quantum fluctuations & grow exponentially
-- important mechanism for early isotropization

11. Proof of concept: isotropization of longitudinally expanding fields in scalar Φ4
Dusling,Epelbaum,Gelis,RV, arXiv:
(arb. lattice units)
Decoherence
EOS
Isotropization

12. Proof of concept: isotropization of longitudinally expanding fields in scalar Φ4
Dusling,Epelbaum,Gelis,RV, arXiv:
(arb. lattice units)
Quantum fluctuations generate an anomalously low viscosity

13. Hydrodynamics from quantum fields:
τ ~ 1/QS
f(p) p ΛS Λ
1/αS
τ >> 1/QS
1/αS p
ΛS=Λ=QS
f(p)
Thermal on long time scales τ ≈(1/αS)2 1/QS :
Λ =T, m2 = Λ ΛS (electric screening), ΛS = αST (magnetic screening)
Isotropization (and hydrodynamics)
can take place on very short time scales ~ 1/QS
Interplay of isotropization vs thermalization:
extract from photon spectra + flow,
di-leptons for pT < M, long range rapidity corr. ?

14. The first fermi: a master formula
increasing
seed size
2500
Also correlators of Tμν
From solutions of B-JIMWLK
Gauge invariant Gaussian spectrum
of quantum fluctuations
3+1-D solutions of
Yang-Mills equations
Expression computed recently-numerical evaluation in progress
Dusling,Epelbaum,Gelis,RV
This is what needs to be matched to viscous hydrodynamics, event-by-event
All modeling of initial conditions for heavy ion collisions includes various
degrees of over simplification relative to this “master” formula

15. IP-Glasma model: match event-by-event Yang-Mills to viscous hydro
2+1-D Yang-Mills +
2+1-D Viscous hydro
2+1-D Yang-Mills

16. Heavy Ion phenomenology: IP-Glasma model
I) Multiplicity distributions
Schenke,Tribedy,RV: PRL108 (2012), ; arXiv: +

17. IP-Glasma model
II) Harmonic flow moments (2+1-D CYM + viscous hydro a la MUSIC)
MUSIC:Schenke,Jeon,Gale (2011) + -
Gale,Jeon,Schenke,Tribedy,RV, + -

18. IP-Glasma model Temperature dependent η/s
Niemi et al PRL106 (2011)
RHIC and LHC have ~ 70% different η/s

19. Heavy Ion phenomenology: IP-Glasma model
Gale,Jeon,Schenke,Tribedy,RV,
Event-by-event flow distributions
vn distributions track eccentricities εn
spatial fluctuations
efficiency => perfect fluidity
momentum anisotropies +

20. Flow moments: analogy with the Early UniverseP
Flow moments: analogy with the Early Universe
Mishra et al; Mocsy- Sorensen
The Universe
HIC
QGP phase
quark and gluon degrees of freedom
hadronization
kinetic
freeze-out
lumpy initial energy density
distributions and correlations of produced particles
Credit: NASA
Δρ/√ρref Δφ
WMAP
HIC-ALICE

21. Jet probes of strongly correlated QGP
J. Milhano, QM12 talk
Radiative energy loss
Broadening due to multiple
Scattering & El. Scat. Energy loss
Modification of color correlations

22. Jet probes of strongly correlated QGP
J. Milhano, QM12 talk
is a measure of the transport properties of the medium
In kinetic theory,
Majumder,Muller,Wang (2007)
Independent measurements of l.h.s & r.h.s test simple quasi-particle pictures

23. Jet probes of strongly correlated QGP
Remarkable pattern of suppression up to 300 GeV!

24. Jet probes of strongly correlated QGP
AdS/CFT
Two extremes for
Jet-Medium interactions
pQCD
Fragmentation functions and differential jet shapes
At the LHC, jets retain
shape but significant
radiation outside cone

25. Jet probes of strongly correlated QGP
Milhano
Simple pQCD model based on soft gluons kicked out of shower by mult. scatt. consistent with di-jet data on x= pt1/pt2 and z

26. Jet probes of strongly correlated QGP
Problem: medum modification of parton shower
Recent progress: in medium splitting has probabilistic interpretation
Mehtar-Tani, Salgado,Tywoniuk,
Casalderrey-Solana,Iancu,
Blaizot,Dominguez,Iancu,Mehtar-Tani,
Implement in MCs: HIJING,Q-PYTHIA,Q-HERWIG,JEWELL,YaJEM

27. Quarkonium probes of strongly correlated QGP
Onium regeneration models give
good description of LHC data
(2S)
Important ingredient: Im V(r)
-- recent progress in NRQCD models
-- AdS & Latt.models show similar trends
Rapp et al., QM2012
See, for eg., T. Hatsuda, QM12 plenary

28. Topology of excited vacuum: Chiral Magnetic Effect
Kharzeev,McLerran,Warringa, NPA (2008)
Sphaleron transitions in external B field
can lead to induced charge separation
– Chiral Magnetic Effect
NCS =
Conventional explanations (charge conservation + v2) exist…
Pratt,Schlichting

29. Topology of excited vacuum: Chiral Magnetic Effect
NCS =
70-80%
0-1% spectator neutrons
Effect disappears with B field…
but v2 is 2.5%
Very preliminary, but if confirmed would be spectacular…
Corollary: isotropization may also proceed through sphaleron decay
Shuryak RV

30. QCD at finite μB
Chiral transition μB=0: Tc=154±9 / 157±6 MeV (hot QCD/ Wuppertal-Budapest)
Some chiral models predict negative
Kurtosis as signature of Critical End Point
Also negative χ6 / χ2
Exciting potential of RHIC high statistics BES !

31. Recap: key questions in heavy ion physics
How is entropy produced and what is the nature of the matter produced ?
How does strongly correlated matter evolve ?
How do hard probes (jets, Onia,…) interact with the matter ?
What can we learn about how emergent features (topological, chiral) of QCD with varying T, μB and B ?
We are making empirical progress on all these fronts, but…
there’s a long way to go before we can claim to understand the
complex collective dynamics of the only accessible non-Abelian Field Theory

32. In the meanwhile,
Happy 75 birthday, Guy !!