Heavy Ion Collisions and the Study of Hot and Dense QCD Matter

Heavy Ion Collisions and the study of hot and dense QCD matter

Javier L Albacete Universidad de Granada

Taller de Altas Energías 2013. Benasque

HIC experimental programs • Past Programs: SIS/LBL, AGS/BNL, SPS/CERN • Present Programs: 1) RHIC/BNL (2000-On): Au-Au @ 200 GeV (also p+p, d+Au, Ca-Ca and lower energies): Discovery machine: First evidence for a new new, strongly interacting state of matter: a “perfect ﬂuid”

Press release Apr ’05 HIC experimental programs • Past Programs: SIS/LBL, AGS/BNL, SPS/CERN • Present Programs: 1) RHIC/BNL (2000-On): Au-Au @ 200 GeV (also p+p, d+Au, Ca-Ca and lower energies): Discovery machine: First evidence for a new new, strongly interacting state of matter: a “perfect ﬂuid”

Press release Apr ’05

2) LHC/CERN (2010-On) : Pb-Pb @ 2.76 TeV (also p+p @ 2.76 TeV and p+Pb @ 5 TeV) Conﬁrmation & Precision machine: quantitative description of the thermal properties of the QGP - I month of running per year starting Nov ’10 - 1 dedicated experiment: ALICE (U. Santiago). CMS and ATLAS also involved in data taking/analysis - So far, excellent accelerator and detectors performances: Data collected ~ 0.15 nb-1 - 2013: p+Pb collisions @ 5 TeV (LHCb also joining!)

Press release Nov ’10 Outline ⇒ Part I

✓ Motivation. QCD & the QCD vacuum ✓ QCD at high temperature or density: Quark Gluon Plasma

⇒ Part II

✓ Heavy Ion collision experiments ✓ Relevant ﬁndings at RHIC and the LHC

5 Goal of HIC experiments: Study hot and dense QCD matter

☛ QCD physics: understanding the QCD vacuum, conﬁnement and chiral symmetry.

☛ Field theory: Emergence of macroscopic (thermal) phenomena from fundamental gauge theories

☛ Cosmology: Reproduce in the laboratory conditions: ~10μs after the Big Bang Microscopic theory ⇒ Quantum Chromodynamics 1 = q¯ (i D m ) q F F µ ⇥ + . . . LQCD f ⇥ f f 4 µ ⇥ flavors = 1, . . . 4 Lorentz index , a quarks q a = 1 . . . Nc = 3 Color index f ⇤ f = u, d, s, c, b, t Flavor index ⇥ µ = 1, . . . 4 Lorentz index gluons Aµ,a ⇥ a = 1 . . . N 2 1 = 8 Color index c

Gauge symmetry: SU(Nc=3) (non-abelian)

+2/3 u (3 MeV) c (1.2 GeV) t (171 GeV) -1/3 d (5 MeV) s (105 MeV) b (4.2 GeV)

7 Strong interactions are responsible for 99% of (visible) matter in the Universe

Electromagnetism Strong interactions

Microscopic theory: QED (p, e,γ ) Microscopic theory: QCD

⇒ (quarks, gluons) ⇒

Macroscopic, collective behavior: Macroscopic, collective behavior: • Phase transitions: gas, solid, ﬂuid, superﬂuid ... • Condensed / solid state physics: Insulators, semi-conductors, ferromagnets, glasses ... ? • Chemistry ... industry

8 Strong interactions are responsible for 99% of (visible) matter in the Universe

Electromagnetism Strong interactions

Microscopic theory: QED (p, e,γ ) Microscopic theory: QCD

⇒ (quarks, gluons) ⇒

Macroscopic, collective behavior: Macroscopic, collective behavior: • Phase transitions: gas, solid, ﬂuid, • What are the phases of QCD ? superﬂuid ...

• Condensed / solid state physics: ... • Is a color-chemistry possible? Insulators, semi-conductors, • Are there color-superconductors? ferromagnets, glasses ... • Color-industry? • Chemistry ... industry ⇒

Study of QCD matter at high density or temperature 9 Properties of QCD: • Asymptotic freedom: The strength of the interaction is smaller at short distances

αs=g2/(4π)

↳↳ smallQCD distances (III): ● The strengthlarge distances of the interaction is smaller at smaller distances: asymptotic freedom.

2 Well understood via αs=g /(4π) perturbative calculations ↳

● Partons carry color SU(3) which is not visible (singlets): conﬁnement.

Heavy-Ion Collisions (I): 1. QCD. 5 Properties of QCD: • Asymptotic freedom: The strength of the interaction is smaller at short distances

• Confinement: Quarks and gluons are not observed as free states. They are conﬁned in color singlet states, hadrons.

mesons (qq)- baryons (qqq) , K, ⇥ . . . p, n, s . . .

⇒Potential models: V (R) = eff + K R R Coulomb Linear

⇒String tension

2 1 K (420 MeV) = 900 MeV fm Properties of QCD: • Asymptotic freedom: The strength of the interaction is smaller at short distances

• Confinement: Quarks and gluons are not observed as free states. They are conﬁned in color singlet states, hadrons. r~ 1/ mesons (qq)- baryons (qqq) , K, ⇥ . . . p, n, s . . .

☛ Would a high-temperature (density) QCD system allow (quasi)free quarks and gluons, i.e a Quark Gluon Plasma?

Heat or pressure Hadron gas QGP

if T then (T ) 1 ⇥ QCD s

12 Hints from Lattice QCD: • The entropy, energy density or pressure of a an ideal (non-interacting) gas are proportional to the # d.o.f: s e p ; ; # d.o.f. T 3 T 4 T 4 / Pion gas ⇣ ⌘ + 0 d = 3 (⇡ , ⇡, ⇡ ) ⇡ ! QGP 7 7 d = d + d = 2 (N2 1)+ 2 2 N N = 37 (for N = 2) q¯qg g 8 q¯q s · c 8 · q¯q · s · f · c f

13 Results from Lattice QCD: • The entropy, energy density or pressure of a an ideal (non-interacting) gas are proportional to the # d.o.f: s e p ; ; # d.o.f. T 3 T 4 T 4 / Pion gas ⇣ ⌘ + 0 d = 3 (⇡ , ⇡, ⇡ ) ⇡ ! QGP 7 7 d = d + d = 2 (N2 1)+ 2 2 N N = 37 (for N = 2) q¯qg g 8 q¯q s · c 8 · q¯q · s · f · c f

• Explosion of degrees of freedom around T= 150 - 180 MeV

• Is there a phase transition around that temperature?

14 Results from Lattice QCD: • The string in potential models ¨melts¨at high temperatures :

Lattice QCD

15 Order of the transition: Phase diagram and broken symmetries • Phase transitions of thermodynamical systems can be related to the restoration of broken symmetries of the system • Phase transitions are signaled by the abrupt changes in the behaviour of the order parameter

OrderFirst orderOrder : discontinuityof the of transition: theSecond transition: order: discontinuity Crossover: continuous in the order parameter in the 1st derivative behaviour parameter

order Water melting into ice Ferromagnets Heavy-Ion Collisions (I): 2. Finite-T QCD. Butter melting 15 (density) (magnetic susceptibility)

16 Heavy-Ion Collisions (I): 2. Finite-T QCD. 15 Heavy-Ion Collisions (I): 2. Finite-T QCD. 15 Phase diagram and broken symmetries • Phase transitions of thermodynamical systems can be related to the restoration of broken symmetries of the system • Phase transitions are signaled by the abrupt changes in the behaviour of the order parameter • Lattice calculations indicate that for realistic quark masses the phase transition from hadronic matter to a QGP at zero baryochemichal potential is actually a crossover

17 Phase diagram and broken symmetries

• QCD with massless quarks can be decomposed into right- and left-handed sectors 1 5 quarks = q¯L i D qL + q¯R i D qR q = q L L(R) 2

u a a u It is invariant under S U L ( N f ) S U L ( N f ) ; exp i L(R) ⇥ d L(R⇥) d L(R) ⇥ ⇤ ⌅ ⇥ QCD (IV): ⇒ Chiral symmetry is spontaneously broken in the vacuum ¯ 0 q¯q 0 = 0 q¯ q + q¯ q 0 (240 MeV)3 L R ● The qqbar potential⇤ | | ⌅ contains⇤ | L R a linearR L| ⌅ term:⇥ The chiral condensate can be regarded as an order parameter for the phase transition string, which breaks when V(rcrit)=mq+mqbar. = 0, for T < T 0 q¯q 0 = c ⇥ | | ⇤ = 0, for T > Tc ● Mass of light mesons and baryons has mainly a dynamical origin. 99% of the mass of visible matter has its dynamical origin in QCD

18 ● The Lagrangian, for 2 massless quarks, is SU(2)L X SU(2)R invariant: chiral symmetry.

● This symmetry is not observed: SSB, Goldstone bosons (pions), ≠0 ⇒ dynamical mass.

Heavy-Ion Collisions (I): 1. QCD. 6 Phase diagram and broken symmetries

• QCD with massless quarks can be decomposed into right- and left-handed sectors 1 5 quarks = q¯L i D qL + q¯R i D qR q = q L L(R) 2

u a a u It is invariant under S U L ( N f ) S U L ( N f ) ; exp i L(R) ⇥ d L(R⇥) d L(R) ⇥ ⇤ ⌅ ⇥

⇒ Chiral symmetry is spontaneously broken in the vacuum ¯ 0 q¯q 0 = 0 q¯ q + q¯ q 0 (240 MeV)3 L R ⇤ | | ⌅ ⇤ | L R R L| ⌅ ⇥ The chiral condensate can be regarded as an order parameter for the phase transition = 0, for T < T 0 q¯q 0 = c ⇥ | | ⇤ = 0, for T > Tc

⇒Other symmetries: Center symmetry Z(Nc) for Polyakov loops (inﬁnitely heavy masses)

1 T 1 = 0, for T < Tc L(⌦x) = tr exp i g A4(, ⌦x) d 0 L(⌥x) 0 = Nc ⇥ | | ⇤ = 0, for T > Tc ⇤0 ⇥ 19 Phase diagram and broken symmetries • The chiral symmetry (Z(Nc)) is restored (broken) above the phase transition:

qq¯ ⇥

L(⇤x) ⇥

20 The QCD Phase diagram. A sketch

Quark Gluon Plasma

critical point? Hadron Gas

• Current understanding of phase diagram is rather speculative due to the lack of reliable theoretical tools or empiric information. Mostly based on models

• It has been suggested that the phase diagram may have a critical point where the ﬁrst order phase transition happening at high baryon density ends

21 ⇒ Part II

✓ Heavy Ion collision experiments ✓ Relevant ﬁndings at RHIC and the LHC HIC experimental programs • Past Programs: SIS/LBL, AGS/BNL, SPS/CERN • Present Programs: 1) RHIC/BNL (2000-On): Au-Au @ 200 GeV (also p+p, d+Au, Ca-Ca and lower energies): Discovery machine: First evidence for a new new, strongly interacting state of matter: a “perfect ﬂuid”

Press release Apr ’05

Press release Nov ’10 Space-time picture of heavy ion collisions. The “little bang” Ion B Hadronic Detection Collision QGP Phase Phase

Ion A

Pre-equilibrium Text Freeze out t=0 ~0.5 fm/c ~10 fm/c ~15 fm/c time

Fireball:

• ~10-15 meters across • lives for ~5x10-23 seconds • Typical LHC event: 5 - TQGP ~ 10 T sun ~ 4 trillion ºC - ~15000 particles detected (l+l-, π’s, γ’s, p’s,resonances...) Observables Ion B Hadronic Detection Collision QGP Phase Phase

Ion A

Pre-equilibrium Freeze out t=0 ~0.5 fm/c Text~10 fm/c ~15 fm/c time

Fireball: Bulk Observables: p ~ ,T ~ 99% of detected particles • ~10-15 meters across • lives for ~5x10-23 seconds - Multiplicities • Initial state: Initials T, ε, μ • Typical LHC event: • Thermal, chemical equilibrium? 5 - TQGP ~ 10 T sun ~ 4 trillion ºC • Thermal radiation, dileptons - ~15000 particles detected - Correlations (collectivity) (l+l-, π’s, γ’s, p’s,resonances...) • Flow, ﬂuctuations, transport • Femptoscopy. • Charge asymmetries: CP Violation Observables

Ion B Hadronic Detection Collision QGP Phase Phase Fast (light and heavy ) quarks and gluons (Energy loss, quenching)

Quarkonia dissociation Ion A Tc, εc

Colorless probes *, ± Pre-equilibrium γ γZ, W Freeze out (control) t=0 ~0.5 fm/c ~10 fm/c ~15 fm/c time

Fireball: Bulk Observables: p ~ ,T Hard Probes: p >> ,T ~ 99% of detected particles • ~10-15 meters across ~ 1% of detected particles • lives for ~5x10-23 seconds - Multiplicities • Produced at very early times • Initial state: Initials T, ε, μ • Medium tomography & diagnosis • Typical LHC event: • Thermal, chemical equilibrium? • Interpretation requires “vacuum” 5 - TQGP ~ 10 T sun ~ 4 trillion ºC • Thermal radiation, dileptons (p+p) and “cold nuclear” (p+Pb) - ~15000 particles detected - Correlations (collectivity): data at the same energy (l+l-, π’s, γ’s, p’s,resonances...) • Flow, ﬂuctuations, transport • Femptoscopy. • Charge asymmetries: CP Violation 1. Before the collision: Non-linear dynamics and saturation • Gluon recombination processes reduce the # of gluons in the wave function before the collision 1 gluon emission BFKL ladder CGC evolution: BFKL ladder fusion

Dilute regime at low energies Dense regime at high “BFKL” energies “BK-JIMWLK”

⌅(x, kt) 2 ⌅(x, kt) (x, kt) (x, kt) (x, kt) ⌅ ln(x0/x) ⇤ K ⇥ ⌅ ln(x0/x) ⇥ K radiation recombination

• In the saturation regime, color ﬁelds become perturbatively strong ~ 1/g. Classical scenario

1 + kt Qs(x) AA† aa [a, a†] 1 /h i⇠↵s ! ⇠

All these effects are accounted for by the Color Glass Condensate effective theory 1. Before the collision: Non-linear dynamics and saturation

• Empiric “conﬁrmation”: RHIC and LHC total multiplicities are a lot smaller than those corresponding to a simple superposition of nucleon-nucleon collisions

MCrcBK 200GeV bMCrcBK 200GeV 10 10 Gaussian nucleon MCrcBK 2.76TeV bMCrcBK 2.76TeV ALICE 2.76TeV ALICE 2.76TeV 8 PHOBOS 200GeV 8 PHOBOS 200GeV /2 /2 part part LHC

/N 6 /N 6 η η Non-linear small-x evolution dN/d 4 dN/d 4 RHIC 2 2

0 100 200 300 400 0 100 200 300 400 Npart Npart

Figure 3. Centrality dependence of charged hadron multiplicity in Pb+Pb collision at √sNN =2.76 TeV and Au+Au collision at √sNN =200GeVfromtheMCrcBKmodelare compared.

However, we should check parameter dependence carefully. For example, if one changes the parameter C in the running coupling, evolution speed changes. In the bottom up scenario [10], the number of gluon produced just after the collision will 2 −2/5 increase by a factor of αs(Qs) during the subsequent evolution of the system. It would be interesting to include such eﬀect into MCrcBK calculations.

3.3. Gaussian shape So far we assumed that nucleus-nucleus collision is described by the incoherent sum of nucleon- nucleon collisions which will occur when transverse distance squared between two nucleons is smaller than the inelastic proton-proton cross section σNN divided by π: σ (x x )2 +(y y )2 NN (10) i − j i − j ≤ π This amounts to assume that nucleon is hard sphere (or disk). However, this approximation may not work in very high energy hadronic collisions. Let us think about the Gaussian shape nucleon in order to take into account the eﬀect of extension of nucleon size as incident energy increases. In this case the thickness function becomes 1 T (r)= exp[ r2/(2B)] , (11) p 2πB − and the probability of nucleon-nucleon collision P (b)atimpactparameterb is

P (b)=1 exp[ kT (b)],T(b)= d2sT (s) T (s b) . (12) − − pp pp p p − ! where (perturbatively) k corresponds to the product of gluon-gluon cross section and gluon density squared. We ﬁx k so that integral over impact parameter becomes the nucleon-nucleon inelastic cross section σNN at the given energy:

σ = d2b (1 exp[ kT (b)]) . (13) NN − − pp ! CERN Initial Glasma ﬁelds

Lappi, McLerran (2006) (Semantics : Glasma ≡ Glas[s - plas]ma) Introduction

Bookkeeping ■ E! B! François Gelis InitialBefore classical the collision, fields, Glasma the chromo- and fields are localized Classical fields in two sheets transverse to the beam axis ● Diagrammatic expansion Lappi, McLerran (2006) François Gelis Glasma flux tubes ● Retarded propagators ■ Immediately after the collision, the chromo-E! and B! fields ● Classical fields 1/Qs CGC Glasma: The● Gluon medium spectrum at LO right after• Immediately the collision after the collision, the chromo-E! and B! fields have become longitudinal : Why small-x gluons matter ● Glasma • ! ! Color Glass Condensate The initial chromo-E and B fields form● Generating longitudinal functional are purely longitudinal and boost invariant : CGC Chromo electric-magnetic fields are longitudinal z i i z ij i j Factorization “flux tubes” extending between the projectiles: Why small-x gluonsE matter = ig , , B = ig" , Factorization Color Glass Condensate 1 2 1 2 Stages of AA collisions A A A A Leading Order Factorization Summary Leading Logs Stages of AA collisions ! " ! " Leading Order 0.8 2 2 Glasma fields Leading Logs 0.8 B z B Initial color fields Glasma fields 2 z Link to the Lund model Initial color fields E 2 z Rapidity correlations Link to the Lund model ] 0.6 E 2 2 z Rapidity correlations ] 0.6 /g 2 B 2 Matching to hydro 4 T Glasma stress tensor Matching to hydro /g 2 B µ) 4 T Glasma stress tensor 2 E Glasma instabilities 0.4 T 2 Glasma instabilities µ) 2 [(g 0.4 ET Summary Summary 0.2[(g 0.2 0 • Flux tubes 1 0 0.5 1 1.5 2 Correlation length in the transverse plane: ∆r Qs− 2 ⊥ ∼ 0 g µτ • 1 0 0.5 1 1.5 2 Correlation length in rapidity: ∆η αs− 2 ∼ g µτ • The flux tubes fill up the entire volume • Glasma = intermediate stage between the CGC and the François Gelis – 2007 Lecture III / IV – Hadronic collisions at theLHC and QCD at high density, Les Houches, March-April 2008 - p. 31 The ridge: extended in rapidity (longitudinal direction) 2-particlequark-gluon20 angular plasma correlations correlations 19 p-p min. bias p-Pb and p-p Nch>110 Pb-Pb Azimuthal asymmetries:

Pantha Rei: RHIC and LHC matter flow!

Elliptic ﬂow h initial geometry Final state momentum d N 2 1 + 2 v2(pt) cos(2) + . . . anisotropy anisotropy d pt d

LHC RHIC Tannebaum ’06

● v2, also called elliptic ﬂow, is usually interpreted in terms of a ﬁnal momentum anisotropy dictated by an initial space anisotropy.

● Ideal hydro: plus an (lattice) equation of state, initial conditions and a hadronization prescription, reproduces data.

● Non-ideal hydro: dissipative (viscous) corrections. (Bulk and) shear viscosity decrease v2.

Heavy Ions: 2. Pre-LHC situation. 7 Azimuthal asymmetries:

Pantha Rei: RHIC and LHC matter flow! Elliptic ﬂow h initial geometry Final state momentum d N 2 1 + 2 v2(pt) cos(2) + . . . anisotropy anisotropy d pt d

LHC RHIC Tannebaum ’06

● v2, also called elliptic flow, is usually interpreted in terms of a final momentum⇒ The fireball expansion anisotropy is very well described dictated by Hydrodynamics: by an initial space anisotropy. µ⇥ • energy-momentum + charge conservation µ T = 0 • local equilibrium + small mean free path jµ = 0 ● Ideal hydro: plus• Equation an (lattice) of state: e(p,T,μ )equation of state,µ B initial conditions ideal fluid dissipative terms (viscosity...) } and a hadronization prescription, reproduces} data. T µ⇥ = [(p, T ) + p] uµu⇥ p gµ⇥ +F ( u⇥ ; ⇥; D . . . ) ⇥µ ● Non-ideal hydro: dissipative (viscous) corrections. (Bulk and) shear viscosity decrease v2.

Heavy Ions: 2. Pre-LHC situation. 7 Flow: Geometry, fluctuations and higher harmonics

lumpy, ﬂuctuating initial conditions initial profile

hydro evolution ideal

viscous hydro evolution

ℓmfp ℓmfp

ALICE n=3 n=4 n=2 n=10 n=15 • Higher harmonics are more affected by dissipative effects

2 2 2 2 N pairs ∝1+ 2v1 cosΔϕ + 2v2 cos2Δϕ + 2v3 cos3Δϕ + 2v4 cos4Δϕ + ...

€ The most perfect fluid (smallest viscosity) ever measured!!

KKP bound derived in the framework of the AdS/CFT correspondence= 1/4Π

Small viscosity strongly indicative of strong coupling behaviour

The produced medium at RHIC and the LHC is far from the expected quasi-free QGP

KKP bound The String Connection (or the weird couple)

• So RHIC matter behaves like a strongly interacting system (perfect ﬂuid, jet quenching..) • So we need a formalism that allows to study strongly coupled systems in real-time formalism (Lattice QCD operates in imaginary time)

The Anti de Sitter / Conformal Field Theory Correspondance (AdS/CFT)

4d world Weakly coupled N=4 SYM in 4d supergravity in = g2 N AdS5×S5 space s c ⇥ Nc Black brane along ⇥ the ﬁfth 1 Finite-T system T = dimension zh 5th dimension Caveats: N=4 SYM is conformal. It is supersymmetric. It includes scalar and fermions. It has no charges in the fundamental representation (quarks)....

Used for: Studies of thermalization and onset of hydrodynamics behaviour, energy loss of soft and slow particles... KKP bound One step back: Does the medium really thermalize?

Photon spectrum: Thermal at low kt The statistical model (II): One step back: Does the medium really thermalize? ● The statistical model gives an good description of particle ratios Relative abundances of different hadronic species well described in statistical inmodel AB, withs (grand T ∼canonicalTc (and ensamble γs∼1 at + RHIC):chemical equilibrium)hint of partonic equilibrium. ● It also works (though not so well) in e+e- and pp(bar): statistical nature of hadronization (cluster models do work).for bosons

Heavy-IonBUT: TheyCollisions also (I): work 6. Hadrochemistry. in e+e- and pp(bar). Statistical nature of thermalization?? 38 Dileptons: ● NA60 sees an excess in the region M<1 GeV/c2, compatible with Softρ -broadeningsector: A (butlot nomore... mass shift).

R lo p x x 1 ● NA60 sees an excess in the 1 • Femptoscopy: Information about the q region 1

R q charm: thermal? out through qlon pion and kaon interferometryNA60 ‘07 Rout

• EM radiation: Photon● PHENIX and low-mass sees an excess in 2 dilepton emissions thefrom region the ﬁreball M<1 GeV/c .

PHENIX ‘07

Heavy Ions: 2. Pre-LHC situation. 33 • Searches for CP-Violation: metastable domains where vacuum excitations violate parity could be created in Heavy Ion Collisions: Another fundamental aspect of QCD probed with heavy ion collsions Phase transition and freeze-out

T [MeV] 170 f S. Mukherjee ’12 System size dependence: 165 talk by S. Das 160 • Fluctuations: search of the critical point: 155 200 150 130 62.4 Freeze-out from LQCD: Higher cumulants, kurtosis in particle 145 17.3 140 talk by S. Mukherjee LGT: Tc(µB) correlations, susceptibilities... Cleymans: PRC 73, 034905 (2006) Andronic: PLB 673, 142 (2009) Dynamical models: STAR: PRC 79, 034909 (2009) poster by P. Huovinen Becattini: PRC 85, 044921 (2012) f µB [MeV] S. Bass, CPOD ’11 0 25 50 75 100 125 150 175 200 225 250 275 talk by H. Petersen Preliminary conclusion: Freeze-out is close to crossover line for energies from !s=200 GeV to !s=17.3 GeV Hard Probes

• They serve as tomographic probes of the produced medium

• Their production rate is well understood in pQCD

• Main RHIC highlight: The produced medium is opaque to the propagation of colored particles

Photons are not suppressed Parton energy-loss

2 x 5 suppresion E sCR qˆ L for hadrons ⇥ ⇤ ⇥ ⇤ Transport coefﬁcient Hadron and Jet quenching at the LHC

Conﬁrmation of the factorization hypothesis Colorless particles (γ, W, Z) unaffected by the medium

Similar suppression of high-pt hadrons and full jets RHIC

hadrons jets

Distinct B-suppression pattern at small pt First observation of B-jet suppression CMS 1 1 1 -1 PbPb sJet = 2.76Anatomy TeV at the LHC Anti-kT (PFlow), R = 0.3 Ldt = 150 µb NN ∫ p > 30 GeV/c • Large fraction of pt-imbalancedPYTHIA+HYDJET pairs. Azimuthal correlation (back-to-backness) similarT,2 to p-p collisions Centrality 0-20% 10-1 • (Hard part of) Jet10 fragmentation-1 functions similar to vacuum. 10-1 120 < p < 150 GeV/c 150 < p < 180 GeV/c Lessons180 < p < from220 GeV/c HI dijets production T,1 T,1 CMS T,1 -2 -2 1 -2 1 1 -1 PbPb s = 2.76 TeV Anti-kT (PFlow), R = 0.3 10 10 Ldt = 150 µb 10 NN PLB 712 (2012) 176 ∫ p > 30 GeV/c CMS PYTHIA+HYDJET T,2 -1 Centrality 0-20% -1 -1 1 1 1 Event Fraction Event Fraction Event Fraction -1 PbPb s = 2.76 TeV Anti-kT (PFlow), R = 0.3 10 10 10 Ldt = 150 µb NN -3 -3 -3 ∫ p > 30 GeV/c 120 < p < 150 GeV/c 150 < p < 180 GeV/c 180 < p < 220 GeV/c PYTHIA+HYDJET 10 T,2 10 T,1 10 T,1 T,1 -1 Centrality 0-20% -1 -1 10 10 10 -2 -2 -2 120 < p < 150 GeV/c 150 < p < 180 GeV/c 180 < p < 220 GeV/c 10Pb 10 Pb 10 T,1 T,1 LessonsT,1 from HI dijets production CMS 1 2 1 2 1 2

-2 -2 1 -2 1 1 Event Fraction Event Fraction Event Fraction -1 PbPb s = 2.76 TeV Anti-kT (PFlow), R = 0.3 10 10 Ldt = 150 µb 10 0 NN π π π0 PLB 712 (2012)π 176 π π0 π π π ∫ p > 30 GeV/c -3 -3 -3 PYTHIA+HYDJET 3 T,2 3 103 3 10 3 3 10 -1 Centrality 0-20% -1 1 -1 1 1 Event Fraction Event Fraction 10 Event Fraction 10 220 < p <10 260 GeV/cmomentum imbalance 260 < p < 300 GeV/c 300 < p 30 GeV/c T,1 T,1 T,1 ∫ PYTHIA+HYDJETp > 30 GeV/c T,2 PYTHIA+HYDJET T,2 1 2 1 2 1 2 -1 -1-1 Centrality 0-20% -1-1 -1 0CMS π π π0 CMS π π0-20% π0 π π π 10-1 Centrality 0-20% 1010 -1 10 -1 10 -1 -1 3 3-1 1 3 3 1 3 3 1 10 10 10 11 220 < p < 260 GeV/c 11 260 < p < 300-1 GeV/c 1 1 300PbPb < p 30 GeV/c 120 < p < 150 GeV/c10 150 < T,1p < 180 GeV/c 180 30 GeV/c T,2 CentralityPYTHIA+HYDJET 0-20% T,2 T,1 T,1 T,1 -1 Centrality 0-20% -1-1 -1-1 -1 1010-1 1010-1 1010-1 10 -2 -2-2 -2-2 -2 -2 -2 -2 120 < p < 150 GeV/c 150 < p < 180 GeV/c 180 < p < 220 GeV/c10-2 1010 -2 10 -2 10 10 10 120 < p < 150 GeV/c10 150 < T,1p < 180 GeV/c 180

-3 -3 -3 Event Fraction Event Fraction Event Fraction 10 10 Event Fraction 10 Event Fraction Event Fraction 10 1010 10 10 Event Fraction -3 10Event Fraction -3-3 10Event Fraction -3-3 10-3 -3 -3 -3 10-3 10 -3 10 -3 10 10 10 10 10 10

1 2 1 21 2 1 1 2 22 1 2 1 2 0 0 0 π π 0 π0 π ππ 1 π0 π2 π ππ0 π 1π π 21 2 1 1 2 22 1 2 1 2 π π π π 13π 23 π π 31 π332 π 3 1 3 2 3 3 0 π π π0 π ππ π0 π π ππ0 π π π 3 3 3 0 3π π 1 π0 22030 < p < π260 GeV/c3 π π 1 π0260 < p < 300ππ GeV/c π 1 π0300π < p < 500 GeV/cπ π π0 π π π 3 3 T,1 3 Δφ 3 T,1 3 3 T,1 13 23 31 332 3 1 3 2 3 3 1 Δφ 1 1,2 3 1 3 3 0 3π π 1 π0 3 π 3 π 1 π0 π π 1 π 2201,2 < p < 260 GeV/c 260 < p < 300 GeV/c 300 < p < 500 GeV/c 220 < p < 260Δφ GeV/c 260 < p < 300 GeV/c 300 < p < 500 GeV/c T,1 T,1 T,1 Δφ 3 3 T,1 3 1,2 3 T,1 3 3 T,1 -1 -1 -1 1 220 < p < 260 GeV/c 1 260 < p < 300 GeV/c 1 300 < p < 500 GeV/c 10 10 10 1,2 T,1 T,1 T,1 10-1 10-1 10-1 Jet quenching is observed as a pronounced dijet pT imbalance in 10-1 10-1 10-1 • 10-2 10-2 10-2 -1 -1 -1 10-2 central collision,10-2 with no visible angular10-2 decorrelation 10 10 10 Event Fraction Event Fraction Event Fraction 10-3 10-3 10-3 Jet quenching is observed as a pronounced dijet pT imbalance in Event Fraction Event Fraction Event Fraction • 10-2 10-2 10-2 10-3 10-3 10-3 1 2 1 2 1 2-2 -2 -2 Yaxian MAO 0 π π π0 π π π0 π 10π π central collision,10 with no visible angular10 decorrelation

IS2013,3 10/09/2013,3 Illa da Toxa, Spain 3 3 3 3 7 Event Fraction Event Fraction Event Fraction Vanderbilt University1 2 1 2 1Δφ 2 0 π π π0 π π π0 π 1,2 π π -3 -3 -3 3 3 3 3 3 3 10 10 10 Δφ Event Fraction Event Fraction Event Fraction 1,2 10-3 10-3 10-3 1 2 1 2 1 2 Yaxian MAO 0 π π π0 π π π0 π π π IS2013,3 10/09/2013,3 Illa da Toxa, Spain 3 3 3 3 7 Vanderbilt University1 2 1 2 1Δφ 2 0 π π π0 π π π0 π 1,2 π π 3 3 3 3 3 3 Δφ 1,2 broadening [jet collimation]

AN IMPORTANT LESSON FROM DATA ⇥ ⇥ 2 large broadening [beyond quasi-eikonal] is a prominent k 2⇤ ⌅ ⇧⇥ qˆ Z - jet correlations k qˆ dynamical mechanism for jet energy loss [dijet asymmetry] ⇥ ⇤ " # " # • Z!e e ,$ $ pT > 60 GeV • Jet: anti-kT, R=0.2, 0.3, 0.4, p >25 GeV, |%|<2.1 •in-medium formation time for small angle and soft gluons T -1 Z - jet correlations [vacuum] is very short k qLˆ • Z-jet separationJet Anatomy > &/2 ! 37at eventsthe LHC for Lint=0.15 nb ⇥ ⇤ Dijet, photon-jet and Z-jet correlations: • Z!e"e#,$"$# p > 60 GeV •democratic broadening is a large effect for soft partons • Large fraction of pt-imbalanced pairs. Azimuthal correlation (back-to-backness) similar to p-p collisionsT •soft radiation decorrelated from jet direction/transported • (HardqLˆ part of) Jet fragmentation functions similar to vacuum. • Jet: anti-kT, R=0.2, 0.3, 0.4, pT>25 GeV, |%|<2.1 to large angles jet Z -1 • Z-jet separationp / p> &/2 ! 37 events for Lint=0.15 nb •enhancement of soft fragments outside the jet T T ET1

jet Z pT /pT 20-80% 0-80% 0-20% ATLAS jet Z • Suppression of the p T / p T relative to MC simulations with no 12 fm energy loss (PYTHIA: Z+jet events) • Stronger suppression for more central collisions ATLAS-CONF-2012-119 QM'2012, Washington D.C. 13/08/2012 B. Wosiek 31

~~Casalderrey-Solana, Milhano, Wiedemann [1105.1760] E~~

0 ● RHIC has measured RAA<1 (e.g. 0.2 for π at midrapidity in central AuAu), and disappearance of back-to-back correlations. ● It is standardly interpreted as the result of partonic energy loss: interplay with the slope of the partonic spectrum. ● Radiative eloss dAA E E dpp characterized by a (E) d P (E + E) dE E E dE density parameter ⇥ ⇥ ⇤ and by medium length / geometry. Heavy Ions: 2. Pre-LHC situation. 29 Ψ A A‘simple’Asimsipmlep example,leexeaxmapmlep:l eJ J : // J / Ψ ssuppressionuspupprpesrseisosnion

A J/Ψ is a cc¯ bound state. A J/Ψ is a cc¯ bound state. hh→J/Ψ 2 2 ij→[cc¯] 2 σ hh→J=/Ψfi(x1, Q ) 2fj(x2, Q ) 2σ ij→([cxc¯1] , x2, Q ) 2 ([cc¯] J/Ψ) σ = fi(x1, Q⊗ ) fj(x2, Q⊗ ) σ (x1, x2, Q"O) ([c→c¯] J/$Ψ) ⊗ ⊗ "O → $ The potential is screened by the medium The potential is screened by the medium The long-distance part is modiﬁed ([cc¯] J/Ψ) 0 The long-distance part is modiﬁed"O ([c→c¯] J/$Ψ→) 0 "O → $ → The J/Ψ production is suppressed [Matsui, Satz 1986] The J/Ψ production is suppressed [Matsui, Satz 1986] What will happen at the LHC Melting of Quarkonia States: A QGP Thermometer?

~~Q Q~~

*From non-relativistic potential theory

Kyoto, Novem •b QQer 20 0(6cc: J/ψ, ψ’, χc... and bb: ϒ, ϒ’, χb... ) statesHa arerd P rexpectedobes to QG Pto– meltp.6 in the medium due to color screening. Herbeumont-sur-Semois,Kyoto, November July2006 2008 H a r d HeavyProbes Ionto Q GPhysicsP – p.6 22 1 1 Strong screening will prevent •bound Sequential state melting: formation.Sequential QQ size~ r Debye Upsilon ~ medium suppression resolution Ebind gT Upsilon suppression is thus expected at the LHC 2010 data 2011 data V (r, T ) efPRLPRLf exp[ 107107 (2011)(2011)m r 052302052302] + K( T ) r ⇥ r D

~~Ágnes Mócsy, Pratt Institute, DNP 2009 22~~

~~>T Y-family suppression~~

~~Lattice QCD~~

~~Indication of suppression Observation of sequential of (Y(2S)+Y(3S)) relative to Y(1S) suppression of Y family 2.4 significance Detailed studies~~

~~Gunther Roland Quark Matter 2012, Washington DC 24 Ψ A A‘simple’Asimsipmlep example,leexeaxmapmlep:l eJ J : // J / Ψ ssuppressionuspupprpesrseisosnion~~

~~Q Q~~

*From non-relativistic potential theory

Kyoto, Novem •b QQer 20 0(6cc: J/ψ, ψ’, χc... and bb: ϒ, ϒ’, χb... ) statesHa arerd P rexpectedobes to QG Pto– meltp.6 in the medium due to color screening. Herbeumont-sur-Semois,Kyoto, November July2006 2008 H a r d HeavyProbes Ionto Q GPhysicsP – p.6 22 1 1 Strong screening will prevent •bound Sequential state melting: formation. QQ size~ r Debye ~medium resolution Upsilon suppression is thus expected at the LHC Ebind gT

~~- Such a a picture starts emerging from data!!~~

~~(a big) BUT!!: Ágnes Mócsy, Pratt Institute, DNP 2009 22~~

- Kinematic cuts affect total yield reconstruction - In-medium spectral functions (imaginary potential, Landau damping...) and transport not yet well understood. - Other cold (shadowing, saturation, absorption) and hot (regeneration) effects not yet well understood - When looked more differentially (pt-distributions, centrality dependence, ﬂow etc) the whole picture does not quite ﬁt yet 38 7 Results 38 7 Results

(a) PbPb sNN = 2.76 TeV (b) pPb sNN = 5.02 TeV v {2, |Δη|>2} (a) PbPb offlinesNN = 2.76 TeV (b) pPb sNN = 5.02 TeV 2 220 ≤ Ntrk < 260 v {2, |Δη|>2} offline 2 v2{4} 220 ≤ Ntrk < 260 v {4} 0.2 0.2 2 v3{2, |Δη|>2} 0.2 0.2 v3{2, |Δη|>2} n n v v n n v v 0.1 0.1 0.1 0.1

0.0 0.0 0.0 2 4 0.06 2 4 6 2 p (GeV/c)4 6 2 p (GeV/c)4 6 p (GeV/c)T p (GeV/c)T T NewsT from the p+Pb run at the LHC (2013) Figure 36: The differential v2 2 and v3 2 values (open markers) as a function of pT obtained Figure 36: The differential v2 2{ and} v3 2{ values} (open markers) as a function ofassocpT obtained for h < 2.4 from long-range{ } two-particle{ } correlations with Dh > 2 for 1 | 2 for 1 < pT < 2 GeV/c v in PbPb and pPb is| shown,| together withThe the differential mattervv22 produced4invalues PbPb (solid| markers)|andin p+Pb pPb as a function collisions of pT for ﬂows!! 3 is shown, together with the differential v2 4{ values} (solid markers) as a function of pT for h < 2.4 obtained with three reference particles{ } in the pT range of 0.3-3 GeV/c. The results refer h| <| 2.4 obtained with three reference particles in the pT range of 0.3-3 GeV/c. The results refer | to| 2.76 TeV PbPb collisions (left)(a) and PbPb to 5.02s TeV= 2.76 pPb TeV collisions (right).(b) pPb s = 5.02 TeV to 2.76 TeV PbPb collisions (left) and to 5.02NN TeV pPb collisions (right). NN v3{2, |Δη|>2} 0.10 0.3 < p < 3 GeV/c 0.10 T v {2, |Δη|>2}, Noffline<20 sub. assoc 3 trk 509 (v2 2, Dh > 2 ) for 1 | 2PbPb)} for 1 < pT < 2 GeV/c, are shown in Fig. 36 in open markers. At a given pT pPb 510 value,{ | v| is observed} to be 3–4 times bigger than v . While the requirement of Dh > 2 com- 510 2 3 value, v2 is observed to be2 3–4 times bigger than v3. While the2 requirement of Dh| >| 2 com- 0.3 < p < 3 GeV/c

511 pletely removes the near-sidev jet-like correlations, additionalv non-hydrodynamical| | correlations T 511 pletely removes the near-side0.05 jet-like correlations, additional non-hydrodynamical0.05 correlations 512 512 from back-to-back jets, as well as effects of energy-momentum conservation on the away side from back-to-back jets, as well as effects ofv2{2, energy-momentum |Δη|>2} conservation on the away side

513 offline 3 0.02 513 of two-particle correlation function could still contaminate the v2 and v3 values obtained from of two-particle correlation function couldv still2{2, |Δ contaminateη|>2}, N <20 the sub.v2 and v3 values obtained from trk v 514 514 two-particletwo-particleMateusz correlations. correlations. Ploskon (ALICE) Jiri Kral (parallel) 45 v2{4}

515 0.00 0.00 515 InIn order order to to further further restrict restrict the the residual residual non-flow non-flow effect effect on on the the away away side, side, the the technique technique of offour- four- CMS data arXiv: 516 particle cumulant is used to extract0 the100 valueoffline200 ( 4 ).300 See section.0 6.2100 for moreoffline200 details about300 0.01 516 particle cumulant is used to0.8 extract the v2vvalue2 v2 (v22-vv242 4). See section.0.8 6.2 for more details about PbPb s = 2.76 TeV Ntrk2 2{ } Ntrk NN 517 this method. Note that no Dh gap is applied here{ } (as well as in the two-particle correlation 517 this method. Note that no D0.6h gap is applied here2 (as2 well as0.6 in the two-particle correlation v2 2+v2 4 518518 method)method) since, since, upon upon correlating correlating four four particles particles at at the the same same time time the the non-flow non-flow correlations correlations are are pPb s = 5.02 TeV 0.4 0.4 NN 519519 naturallynaturally suppressed, suppressed, especially especially for for high high multiplicity multiplicity events events (in (in fact, fact, it isit issuppressed suppressed by by an an 40 0.00 7 Results 520520 additionaladditional factor factor of of 1/ 1/NNasas compared0.2 compared to to two-particle two-particle correlation correlation0.2 method). method). The The measured measuredv2 v42 4 0 100 200 300 0 100 200 { 300}{ } 0 100 200 300 521521 valuesvalues as as a afunction function of ofpTpareT are also also shown shown in in Fig. Fig.offline 36 36 in in solid solid markers. markers. As As one one can canoffline see, see,v2 v42 4is is Ntrk Ntrk { }{ } offline 522522 belowbelowv2v22 2overover the the whole wholepTprange,T range, with with similar similar behavior behavior in in pPb pPb and and PbPb PbPb collisions. collisions. This ThisarXiv:1305.0609& is is arXiv:1305.0609& { {} } 532 fluctuations could be estimated from Eq. 30, if one assumes that hydrodynamic flow would beNtrk 523523 expectedexpected because because the the event-by-event event-by-eventv vfluctuation2 fluctuation contribute contribute to tov v42 4andandv v22 2inin opposite opposite • v2!is!smaller!in!2533 pPbthe only!than!in! source ofPbPb correlations2!{ {} } in v22{ 2}{ and} v2 4 . Considering that this could be the case, then 524524 ways,ways, approximately approximately following following the the relations: relations: { } { } • Peripheral!subtracYon!has!a!small!effect!at!high!mulYplicity• v3!is!essenYally!the!same!in!! pPb!and!PbPb;!!turns!on!at!N~40T50! 2 • 2 sv v 2 vPeripheral!s4 ubtracYon!makes!almost!no!difference! v 2 = < v >2 +2 s2 ,2v 4 = < v >2 2 s2 ,2 2 = 2 (30){ } 2{ }. (31) 2v2 2 = <2v2 > +v2sv2 ,2v2 4 = <2 v2 > v2sv2 ,2 (30) 2 { {} } { {} } v2 s v2 2!Shengquan+ v2 4 !Tuo!(Vanderbilt)!! pA2013, ECT, Trento, May 6-10,2013 21 qq qq { } { } !Shengquan!Tuo!(Vanderbilt)!! pA2013, ECT, Trento, May 6-10,2013 19 525525 whichwhich always always results results in in a largera larger value value for forv2v2 2thanthanv2v42 4. . 534 The{ {} results} { for{} pPb} and PbPb collisions are shown in the bottom panel of Fig. 37, indicating 526526 Fig.Fig. 37 37 shows shows the the multiplicity multiplicityBut dependence it dependence does535 about of ofnotv2v 45–55%2 2, vquench,2v42v42andfluctuationsandv3 v23jets!!2for infor 1 PbPb< 1

- ALICE, CMS and ATLAS at the Heavy Ion Town meeting, CERN 29 Jun 2012 http://indico.cern.ch/event/HItownmeeting - ALICE, CMS and ATLAS contributions to the Preparatory Group for a European Strategy for Particle Physics

~~LHC: RHIC: • End of Phase0 (2010-2013). -1 - 0.15 nb in Pb-Pb coll √sNN = 5.5 TeV - Feb 2013: p-Pb run (5TeV, ∫dt L ~ 30nb)~~

~~•2013-2014: Long Shutdown 1. - ALICE, CMS and ATLAS detector upgrades~~

~~• Phase1 (2015-2017) -1 - 1-3 nb Pb-Pb at √sNN = 5.5 TeV - Reference data p-p, p-Pb √sNN = 5.5 TeV~~

~~• 2018 Long ShutDown2 - Significant detector upgrades~~

• Phase2 (2019-beyond) - Focus on energy scan and varying initial conditions (nuclei) - - Luminosity increase to 6x1027cm-1s-1 Polarized target: Spin physics -1 - Goal: O(10 nb ) in Pb-Pb at √sNN = 5.5 TeV - Lighter nuclei

Others: Planned facilities involving high-energy nuclear reactions EIC (Electron Ion Collider), LHeC (Large hadron- electron collider), FAIR (GSI; Facility for antiproton & ion research) would provide complementary studies. Back up slides Finite-TLattice QCD QFT: ● In the grand-canonical ensemble, the thermodynamical properties of a system in thermodynamical equilibrium are given by (see Karsch, Lecture Notes in Physics ‘02):

~~● With a rotation to Euclidean space -it→1/T and imposing (anti)periodic boundary conditions for (fermions) bosons,~~

~~● The partition function may be computed perturbatively, or by discretization and Monte Carlo methods: lattice QCD.~~

Heavy-Ion Collisions (I): 2. Finite-T QCD. 10 One step back: Does the medium really thermalize? Transport models: ● Ideal hydro is the extreme version of transport for very large opacities. If thermalization/isotropization is not achieved, small deviations can be dealt with through viscous corrections, but large deviations require transport: relativistic Boltzmann equation.

● Parton transport now includes 2↔2 and 2↔3 reactions (BAMPS): accelerates isotropization. ● Hadron transport includes many reactions/species (AMPT, UrQMD). Heavy-Ion Collisions (I): 3. Dynamics of heavy-ion reactions. 23 Hagedorn Temperature ⇒Bag model: Hadrons are “droplets” of perturbative Non-perturbative vacuum vacuum with quasi free quarks and gluons inside: NP < 0 2R x 4 ⇥ H = H + H + + R3B + . . . bag kin bag · · · ⇥ R 3 perturbative Bag 4 vacuum B pert Non pert (250 MeV) = 0 constant ⇥ ⇥ pert

50 ⇒Bag model: Hadrons are “droplets” of perturbative Non-perturbative vacuum vacuum with quasi free quarks and gluons inside: NP < 0 2R x 4 ⇥ H = H + H + + R3B + . . . bag kin bag · · · ⇥ R 3 perturbative Bag 4 vacuum B pert Non pert (250 MeV) = 0 constant ⇥ ⇥ pert

~~⇒Potential models. Lines of color field are confined to flux tubes or strings V (R) = eff + K R R String tension: 2 1 R K (420 MeV) = 900 MeV fm ⇥ ⇤ V (R)~~

~~1 2 3 4~~

~~-5 R~~

~~51 Vacuum at T=0 Pion Gas T>0~~

~~⇒ Pressure and energy density of ideal Bose (and Fermi) massless gas 2 ⇥ 4 0 Pion gas: p d T , = 3 p , d = 3 (⇥±, ⇥ ) 90~~

~~52 Vacuum at T=0 Pion Gas Quark-Gluon Plasma~~

+ 0 d = 3 (⇡ , ⇡, ⇡ ) ⇡ ! ⇒ Pressure and energy density of ideal Bose (and Fermi) massless gas 2 ⇥ 4 0 Pion gas: p d T , = 3 p , d = 3 (⇥±, ⇥ ) 90 ⇥2 ⇥2 p d T 4 B , d T 4 + B QGP: QGP ⇥ gqq¯ 90 QGP ⇥ gqq¯ 30 7 7 d = d + d = 2 (N 2 1) + 2 2 N N = 37 (N = 2) gqq¯ g 8 qq¯ s · c 8 · qq¯ · s · c · f f

~~53 pressure energy density 14~~

~~12 4 QGP/ T pQGP 10 8~~

pgas 6 4 / T4 2 's Tc 0 0 50 100 150 200 250 0 50 100 150 200 250 T (MeV) T (MeV) T 140 MeV c 3 Latent heat of the phase transition: L = QGP (Tc) s 4B 1GeV fm ⇥ ⇥ 3 Energy density of nuclear matter 0.15 GeV fm nm

~~QGP T QGP 170 MeV 2 1012 Kelvins c ⇤ ⇥ · 7 Sun core TSun 1.5 10 Kelvins ⇥ · T 103 Kelvins Córdoba C´ordoba~~

~~54 Energy density & pressure Results from Lattice QCD~~

~~Stephan-Boltzman (ideal gas) limit~~

~~“Explosion” of degrees of freedom T 170 180 MeV c ⇥ ÷~~

~~For an ideal gas = 3p T 4 The “trace anomaly” T µ = 3p µ is a measure of the interaction (and also of the degree of violation of scale symmetry)~~

~~55 Debye screening of the heavy quark potential in the QGP phase • The presence of free quarks and gluons around a heavy quark pair screens the interaction.~~

~~• The string tension tension goes to zero V (r, T ) eff exp[ m r] + K(T ) r ⇥ r D Debye mass 1 Nc + Nf m2 = 2 g2 T 2 D 3~~

~~effective string tension >T K(T ) 0 for T >> T c~~

~~Lattice QCD~~

~~56 ⇒Other way for the QGP: compressing nuclear matter at low temperatures Baryon number density ~ Baryochemical potential 1 N N T 3 µ 1 µ 3 n = q q¯ = d B + B B 3 V · 6 T ⇥2 T ⇤ ⇥ ⌅~~

~~µB < µBc µB > µBc Pressure of a Fermi gas: T 4 7⇥2 1 µ 2 1 µ 4 p = d + B + B F · 3 120 4 T 8⇥2 T ⇤ ⇥ ⇥ ⌅~~

~~57 ⇒Other way for the QGP: compressing nuclear matter at low temperatures Baryon number density ~ Baryochemical potential 1 N N T 3 µ 1 µ 3 n = q q¯ = d B + B B 3 V · 6 T ⇥2 T ⇤ ⇥ ⌅~~

µB < µBc µB > µBc Pressure of a Fermi gas: T 4 7⇥2 1 µ 2 1 µ 4 p = d + B + B F · 3 120 4 T 8⇥2 T ⇤ ⇥ ⇥ ⌅ Critical baryochemical potential for the QGP phase transition (T=0) p (µ ) = B = µ 3⇤⇥ B1/4 1.1 GeV qq¯ Bc ⇥ Bc Nuclear matter: µ 0.9 GeV B nm 58 Putting all together: The phase diagram of QCD

• At low the phase transition is smooth • At larger the transition becomes ﬁrst crossover between hadron gas and QGP. order. Existence of a critical point. More like melting butter More like water-vapor transition

~~crossover~~

~~critical point ﬁrst order~~

• A number of phases, Color Superconductivity (2SC), Color Flavor Locked (CFL) ... have been proposed. Lattice methods not reliable ready in this regime .... 59 Where to ﬁnd the QGP? ⇒Heavy ion collisions ⇒ Core of neutron stars may be composed “exotic” quark matter M 1 2 M ; R 10 km NS ⇥ ÷ Sun NS ⇥ ⇒ Early Universe: The temperature of the Universe at time10-4~10-5 seconds was Tuniv~ 200 MeV. It went through a phase transition from quarks and gluons to hadrons

~~Early Universe~~

~~Heavy Ion Collisions~~

~~Neutron Stars ?~~

~~60 Relativistic Heavy Ion Collider (RHIC) Large Hadron Collider (LHC) Alternating Gradient Synchrotron (AGS) Super Proton Synchrotron (SPS) @ Brookhaven National Lab (BNL) @ CERN~~

~~Lab years sNN (GeV) AGS BNL 87/99 5 SPS CERN 86/02 17 RHIC BNL 01/?? 200 Au-Au, d-Au, p-p, Cu-Cu LHC CERN ??/?? 5500 Pb-Pb, p-Pb, p-p~~

• First hints of QGP formation at SPS. More conclusice evidence obtained at RHIC • Of the 4 big experimental collaborations at the LHC, one (ALICE) is fully dedicated to HIC. Other two (ATLAS and CMS) will perform related measurements 61 Locating HIC experiments on the QCD phase diagram: • The baryon density in the midrapity region decreases with increasing collison energy p + p = ln 0 z p0 pz increasing collision energy High energy: valence quarks are not slowed down by the collison

~~• The temperature increases with collision energy~~

~~LHC~~

~~Increasing collision energy~~

~~62 Space-time view of heavy-ion collisions hadronic phase QGP and and freeze-out initial state hydrodynamic expansion~~

~~pre-equilibrium hadronization~~

~~= cte Detected particles T 100 MeV + x free streaming x 10 fm Hadron Phase 7 fm hadrons Quark-Gluon Plasma QGP T 300 MeV 1 fm Pre-equilibrium = 0 fm Ultra-relativistic nuclei~~

We lack of a uniﬁed description of the collision dynamics at all times 63 The Initial State: Color Glass Condensate & Saturation p + p Y = ln 0 z p0 pz linear evolution (DGLAP, BFKL), dilute regime gluon radiation pz Ng P Ng kz = x pz Y exponentially growing gluon densities

~~64 The Initial State: Color Glass Condensate & Saturation p + p Y = ln 0 z p0 pz linear evolution (DGLAP, BFKL), dilute regime gluon radiation pz Ng P Ng kz = x pz Y~~

~~gluon recombination Non-linear evolution (CGC), high density~~

N g P N R N 2 Y ⇥ g g Y • At high energies (large rapidities, small-x), the hadron wavefunction reach saturation due to the growing importance of recombination processes Rs 1 Qs kt < Qs(Y ) Rs • Saturation is enhanced in nuclei (large # of gluons, even at low energies) 2 1/3 2 1/3 ⇒ 2, RHIC 2 QsA A Qsp ⇒ A 665 QsAu 1 2 GeV ⇥ ÷ Bulk properties of RHIC matter: Multiplicities Predictions before RHIC vs data • One expects the total # of produced dN hadrons to be proportional to the # of d =0 partons in the wavefuncttin of colliding incoherent p+p nuclei superposition • First surprise at RHIC: Total multiplicities came out a lot smaller than predicted by simple superpositions of proton-proton collisions: sNN • Saturation explanation: The ﬂux of 800 dNch colliding partons (mostly gluons) is dη 700 reduced due to saturation effects 600 500

~~• CGC predictions account the energy 400 Au-Au 0-6%, s =200 GeV rapidity, centrality of the multiplicities 300 NN~~

~~200 Au-Au 0-6%, sNN=130 GeV ... CGC has been discovered at RHIC... 100~~

-4 -2 0 2 4 66 η The success of hydrodynamics at RHIC ⇒ Hydrodynamics is an effective theory that describes the long wavelength modes of the conserved charges of the system µ⇥ energy-momentum conservation: µ T = 0 µ baryon number conservation: µ jB = 0 1 ⇒It requires local equilibrium and a small mean free path: mfp (⇥ n) 0 ⇥

~~ideal ﬂuid dissipative terms (viscosity...) } } T µ⇥ = [(p, T ) + p] uµu⇥ p gµ⇥ +F ( u⇥ ; ⇥; D . . . ) ⇥µ~~

67 ⇒ Ideal hydro describes a lot of RHIC data!! Input for hydro evolution: Photon spectrum • QGP E.oS. • short thermalization time: 0.6 1 fm therm ⇥ ÷ • initial energy density: 30 GeV/fm3 therm hadron spectrum