Introduction to the physics of the Quark-Gluon Plasma and the relativistic heavy-ion collisions

Transcription

1 Introduction to the physics of the Quark-Gluon Plasma and the relativistic heavy-ion collisions Villa Gualino-orino,

2 Matter under extreme conditions Fermi Notes on hermodynamics QGP Eleven Science Questions for the New Century NAIONAL RESEARCH COUNCIL OF HE NAIONAL ACADEMIES No. 7 - What Are the New States of Matter at Exceedingly High Density and emperature? QGP is at >10 1 K and ρ > cm -3

3 Let s s start from 100 years ago p p Rutherford discovered the Nucleus In 30 started the study of a new force: Nuclear Force between nucleons p,n,λ,σ,,.. π,ρ,ω,φ,κ,.. Bashing nucleons with increasing energy It became clear that nucleons and more generally hadrons are made of quarks exchanging gluons In 1974 the theory of the strong interaction was written down and called Quantum Chromodynamics

4 L QCD = f Quantum Chromodynamics i ψ n µ µ λ a 1 ψ iγ µ ga a i m iψ iψ i i = 1 4 a µν µ ν ν µ F a = Aa Aa + Similar to QED but 3 charges + gauge invariance imply that the gauge field (gluons) self-interact: - Asymptotic freedom - Confinement wo regimes: - Q>>Λ QCD one can use perturbative QCD (pqcd) - Q ~Λ QCD, Q >Λ QCD non perturbative methods : i f abc A µ b A µ c lattice QCD (lqcd) and effective lagrangian approach F µυ a F µυ a electric charge colour charge

5 Quark-Gluon Plasma Inside nuclei strong interaction manifest in an extremely non-perturbative regime (Λ QCD ~ 1 fm -1 ) and quarks are not the relevant degrees of freedom Several arguments already in the lead to think that at some temperature and/or density quarks can roam freely in a medium -> QGP 1) ASYMPOIC FREEDOM At large there are interaction q ~ (3) and the coupling is weak ) OVERLAP (percolation) Hadrons Overlap does not allow to identify the hadrons itself: 0 ~ 150 MeV 3) BAG PRESSURE MODELING Pressure of pion gas smaller than the quark gas one: 0 ~ 150 MeV 4) HAGERDON LIMIING EMPERAURE Hadron gas partition function has a singularity at 0 ~ 160 MeV

6 Hagerdon s limiting temperature From the Hadronic side increasing temperature leads to the production of higher mass hadronic states, but the density of states grows exponentially with the mass Partition functon for a gas o particle with density of states ρ(m) Hagerdon, Nuovo Cimento (1965): 0 is a limiting temperature for hadronic systems Cabibbo-Parisi, PLB59(1975): Divergency of the partition function has to be associated with a phase transition of hadronic matter to quark-gluon matter m>>

7 Quark-antiQuark free energy in lqcd lqcd Charm Quarks String breaking We cannot observe quarks, but at large we can envisage a weakly interacting gas of quarks and gluons vacuum Asymptotic value Kaczmarek et al., PPS 19,560(004)

8 Order Parameters of the Phase ransition L Polyakov Loop Chiral Condensate lqcd ~170 MeV ~170 MeV r ( ) r ig A ( x, t dτ βh e = r( e ) β 0 0 ) int qq (50 MeV ) 3 0 What is the order of the phase transition? [Ratti]

9 he basic relations of reference Ideally our reference is a gas of non-interacting massless quarks and gluons Multiplied by degrees of freedom d q+q =**3*N f =4-30, d g =8* x d.o.f x d.o.f

10 From lattice QCD ε SB π = + g d q q + d RHIC µ B =0 Interaction measure RHIC LHC Enhancement of the degrees of freedom towards the QGP ε c c 0.7GeV fm 175 ± 15 MeV Stefan-Boltzmann limit not reached by 0 % for ε: QGP as a weak interacting gas?! In Ads/CF this can be a very strong interacting system No interaction means also ε=3p (for a massless gas) / [Cotrone] 3

11 QGP in the Early Universe Evolution e. m. decouple (~ 1eV, t ~ ys) thermal freeze-out but matter opaque to e.m. radiation Atomic nuclei (~100 KeV, t ~00s) chemical freeze-out Hadronization (~ 0. Quark and gluons ~ 0. GeV,, t~ 10-5 s) Bang

12 Degrees of freedom in the Universe g() g( ) = BBN + e e annihilation g s g ε ε 4 HIC QCD transition [MeV] MSSM SM EW transition g( ) = γ e ν µ π g uds cb 10-5 s Quark-Gluon Plasma D.J.Schwartz, Ann. Phys. 004

13 How to produce a matter with ε >>1 GeV/fm 3 lasting for τ > 1 fm/c in a volume much larger than an hadron? Let s bash again at higher energy

14 High Energy Heavy Ion Collision Facilities Accelerator AGS ( 80s) SPS (94- ) RHIC (00- ) LHC (09- ) Fixed target Collider Lab. BNL CERN BNL CERN E beam [AGeV] 10 (*) 160(*) s me NN beam s E NN beam 4.5 s[ AGeV] Contrac tion s = = NN ( pa + pb ) ECMS γ CM = E = m Max energy density complete stopping E 3γ sn CM part ε max = = = 3 V 4π R A 3sN part 3 4π mr s m RHIC -> ε max ~ 10 GeV/fm 3 LHC -> emax~ GeV/fm 3

15 LHC Exploring the phase diagram RHIC nuclei new medium created from the energy deposited µ B =0 (quark=antiquarks) Hotter-denser denser-longer increasing E beam ime 5-15 fm/c = 15-45ys~10 - s RHIC SPS Increasing beam energy -> transparency Energy distributed in a larger volume How to make simple estimates?

16 F. Becattini Statistical Model analysis emperature Yield Mass Quantum Numbers Hagerdon limiting temperature AGS (BNL) Chemical Potential SPS(CERN) RHIC (BNL)

17 Energy Density and emperature Estimate I ε 0 = y E V z = v = tanh y z z t dz =τ cosh y dy Energy density a la Bjorken: = 0.5 E A N z = m πr Particle streaming from origin τ 0 N y theory estimate = τ RHIC ~0.6-1 fm/c 1 πr τ ε RHIC ~ 5 8 GeV/fm 0 de dy experiments de /dy ~ 70 GeV We can estimate the initial ε 0 3 Is this correct?

18 Energy Density and emperature Estimate II 3 S sv = cost s τ = sτ τ = τ = But this means that the previous estimate cannot be correct because it supposes that ε τ 1, but to conserve entropy ε τ 4/3 ε 1D expansion 1 / 3 1 de τ f = = ε Bjorken GeV fm πr τ 0 dy τ 0 Estimate of QGP lifetime (τ 0 ~0.6 fm/c at RHIC) τ QGP 0 0 = τ c Entropy Conservation 1/ 4 30 ε fm 1.7 fm MeV g = = = π 3 1/ 4 RHIC - = c > τ QGP =0.6* 3 =5 fm/c τ = τ LHC - =3.5 c > τ QGP =0.4*3.5 3 =15 fm/c ε = ε 4/3 τ 0 0 τ So with urhic ε 0 >>ε c τ QGP >1fm/c V> 10 3 fm 3

19 Different stages of the Little Bang System expands and cools down ( t ) 1/ = cost τ = z Freeze-out Hadron Gas Phase ransition Plasma-phase Pre-Equilibrium τ ~0 fm/c τ ~5 fm/c τ ~0.6 fm/c τ <0. fm/c

20 Soft and Hard probes SOF (p ~Λ QCD,) driven by non perturbative QCD Hadronyields, collectivemodesof the bulk, strangenessenhancement, fluctuations, thermal radiation, dilepton enhancement HARD (p >> Λ QCD ) Early production, pqcd applicable, comparable with pp, pa jet quenching, heavy quarks, quarkonia, hard photons 95% of particles

21 he Several Probes [Romatschke], [Snellings],[Beraudo] Initial Conditions Quark-Gluon Plasma Hadronization BULK (p ~) CGC (x<<1) MINIJES Heavy Quarks Gluon saturation (p >>,Λ QCD ) (m q >>,Λ QCD ) [Albacete] [Bruna] [Arnaldi] Microscopic Mechanism Matters! [Becattini] [Blume] Initial Condition exotic non equilibrium CGC Bulk Hydrodynamics BU finite viscosities (η,ζ) Minijets perturbative QCD BU strong Jet-Bulk talk Heavy Quarks Brownian motion (?) BU strongly dragged by the Bulk Quarkonia Are suppressed (only resonances?) or regenerated Hadronization Microscopic mechanism can modify QGP observables

22 RHIC LHC Dominance of QGP phase (τ( QGP QGP > 10 fm/c) Vanishing hadronic contamination? A new QGP phase: perturbative plasma? Hopefully with several other surprises Larger η/s we get close to the pqcd estimates? Enjoy the School! Very large yield of heavy quark (m( q >>) ) and jets (p( >> Increasing relevance of non-equilibrated objects! Existence of a primordial non-equilibrium phase Color Glass Condensate (CGC) as high-energy limit of QCD? >>)

23 Collective Expansion of the Bulk y x z ε = For the first time close to ideal Hydrodynamics x y y SPS RHIC v /ε measures efficiency in converting the eccentricity from Coordinate to Momentum space + x x η/s viscosity c s =dp dp/dε EoS v = p p x x + p p y y p y he fluid with lowest ever observed η/s QGP p x Viscosity η/s ransverse Density [fm - ]

24 Color Glass Condensate initial conditions? x = Parton distr. funct At small x (p ) dense gluon matter Gluons of small x (p ) -> larger size >1/Q s overlap and the gluon dostribution stops growing p e y s Q xg x Q ( A πr (, ) sat s) α s( Q ) 1/3 dn/d p Ideal Sketch Q sat (s) p At RHIC Q ~ GeV At LHC Q ~? What is the impact of a different intial condition?

25 Suppression of minijets Jet Quenching Jet triggered angular correl. Suppression should increase with density and temperature. Allows a further measure of energy density. It is due to gluon radiation? Jet energy loss produce mach cones? y x ϕ near Medium away

26 Heavy Quarks dragged by the medium? - m c,b >> Λ QCD produced by pqcd processes (out of equil.) - τ 0 << τ QGP they go through all the QGP lifetime c,b >> 0 no thermal production -m c,b A better test of pqcd scattering and energy loss: - m Q >>m q small drag from the bulk Indirect measurement from semileptonic decay (D->Keν) came as a surprise: Strong suppression Large elliptic Flow

27 Quarkonia Suppression? QQ Quarkonium dissoved by charge screening: hermometer V α eff e m r D r r QQ 1 m D 1 g χ c, J/Ψ, χ b, Y, More binding smaller radius higher temperature Suppression at SPS! More suppression at RHIC because of high the higher temperature?! and even more at LHC?

28 Baryon/Mesons Hadronization Modified Au+Au PHENIX, PRL89(003) p+p Use medium and not vacuum -> > Quark coalescence More easy to produce baryons! dn d = M fa ( ra, pa ) fb( rb, pb ) Φ 3 M P a, b ( r, q ) ab ab Quark number scaling v v,m,b (p1 (pn ) v p V ) 3v n Baryon (p (p /) /3) Hadronization is modified Dynamical quarks are visible,q,q Meson Fries-Greco-Sorensen - Ann. Rev. Part. Sci. 58, 177 (008)

29 Hadronization Modified Baryon/Mesons Au+Au PHENIX, PRL89(003) p dn d p dnq = dp dφ H p dn q dp ( p ) p+p [ 1+ v cos( )] ϕ dnq ( p n) d p n GKL Quark number scaling v q fitted from v π Coalescence Enhancement scaling of v v (p 1) v p (p /),M,q V v (p n) 3v n (p /3),B,q Dynamical quarks are visible Collective flows