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

Introduction to the physics of the Quark-Gluon Plasma and the relativistic heavy-ion collisions. Villa Gualino-Torino, 7-3-2011. Matter under extreme conditions…. Fermi Notes on Thermodynamics. QGP. Eleven Science Questions for the New Century

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

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  1. Introduction to the physics of the Quark-Gluon Plasma and the relativistic heavy-ion collisions Villa Gualino-Torino, 7-3-2011

  2. Matter under extreme conditions… Fermi Notes on Thermodynamics QGP Eleven Science Questions for the New Century NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES… No. 7 - What Are the New States of Matter at Exceedingly High Density and Temperature? QGP is at T>1012K and r > 1040 cm-3

  3. p,n,L,S,D,.. p p p,r,w,f,K, .. Let’s start from 100 years ago … 1911 - Rutherford discovered the Nucleus In ’30 started the study of a new force: Nuclear Force between nucleons 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. Quantum Chromodynamics electric charge colour charge • Similar to QED but 3 charges + gauge invariance • imply that the gauge field (gluons) self-interact: • Asymptotic freedom • Confinement Two regimes: - Q>>LQCD one can use perturbative QCD (pQCD) - Q ~LQCD , Q >LQCDnon perturbative methods : lattice QCD (lQCD) and effective lagrangian approach

  5. Quark-Gluon Plasma Inside nuclei strong interaction manifest in an extremely non-perturbative regime (LQCD~ 1 fm-1) and quarks are not the relevant degrees of freedom Several arguments already in the ’70-’80 lead to think that at some temperature and/or density quarks “can roam freely in a medium”-> QGP 1) ASYMPTOTIC FREEDOM At large T there are interaction q2~ (3T)2 and the coupling is weak 2) OVERLAP (percolation) Hadrons Overlap does not allow to identify the hadrons itself: T0~ 150 MeV 3) BAG PRESSURE MODELING Pressure of pion gas smaller than the quark gas one: T0~ 150 MeV 4) HAGERDON LIMITING TEMPERATURE Hadron gas partition function has a singularity at T0 ~ 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 r(m) m>>T Hagerdon, Nuovo Cimento (1965): T0 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

  7. Quark-antiQuark free energy in lQCD We cannot observe quarks, but at large T we can envisage a weakly interacting gas of quarks and gluons Asymptotic value Charm Quarks String breaking vacuum lQCD Kaczmarek et al., PPS 129,560(2004)

  8. Order Parameters of the Phase Transition Polyakov Loop Chiral Condensate T~170 MeV T~170 MeV lQCD What is the order of the phase transition? [Ratti]

  9. The basic relations of reference Ideally our reference is a gas of non-interacting massless quarks and gluons x d.o.f x d.o.f Multiplied by degrees of freedom dq+q=2*2*3*Nf =24-30 , dg=8*2

  10. From lattice QCD Enhancement of the degrees of freedom towards the QGP RHIC Stefan-Boltzmann limit not reached by 20 % for e : QGP as a weak interacting gas?! In Ads/CFT this can be a very strong interacting system mB=0 Interaction measure [Cotrone] RHIC No interaction means also e=3p (for a massless gas) LHC

  11. Bang QGP in the Early Universe Evolution • e. m. decouple (T~ 1eV , t ~ 3.105 ys) • “thermal freeze-out “ • but matter opaque to e.m. radiation • Atomic nuclei (T~100 KeV, t ~200s) • “chemical freeze-out” • Hadronization (T~ 0.2 GeV, t~ 10-5s) • Quark and gluons

  12. Degrees of freedom in the Universe 10-5s HIC g(T) Quark-Gluon Plasma D.J.Schwartz, Ann. Phys. 2004

  13. How to produce a matter with e >>1 GeV/fm3 lasting for t > 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 Fixed target Max energy density complete stopping Collider RHIC -> emax~ 102 GeV/fm3 LHC -> emax~ 3 103 GeV/fm3

  15. LHC Exploring the phase diagram RHIC SPS Time – 5-15 fm/c = 15-45ys~10-22s RHIC nuclei new medium created from the energy deposited mB=0 (quark=antiquarks) Hotter-denser-longer increasing Ebeam Increasing beam energy -> transparency Energy distributed in a larger volume How to make simple estimates?

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

  17. Energy Density and Temperature Estimate I Particle streaming from origin Energy density a la Bjorken: theory estimate experiments tRHIC~0.6-1 fm/c dET/dy ~ 720 GeV We can estimate the initial e0 Is this correct?

  18. Energy Density and Temperature Estimate II Entropy Conservation 1D expansion But this means that the previous estimate cannot be correct because it supposes that e ~ t-1, but to conserve entropye ~ t-4/3 So with uRHIC e0>>ec tQGP>1fm/c V> 103 fm3 Estimate of QGP lifetime (t0~0.6 fm/c at RHIC) RHIC - T=2Tc->tQGP=0.6*23 =5 fm/c LHC - T=3.5 Tc -> tQGP=0.4*3.53 =15 fm/c

  19. Different stages of the Little Bang System expands and cools down t~20 fm/c 2 Freeze-out Hadron Gas Phase Transition Plasma-phase Pre-Equilibrium t~5 fm/c t~0.6 fm/c t<0.2 fm/c

  20. Soft and Hard probes SOFT (pT ~LQCD,T) driven by non perturbative QCD 95% of particles Hadron yields, collective modes of the bulk, strangeness enhancement, fluctuations, thermal radiation, dilepton enhancement HARD(pT >> LQCD) Early production, pQCD applicable, comparable with pp, pA jet quenching, heavy quarks, quarkonia, hard photons

  21. The Several Probes [Romatschke], [Snellings],[Beraudo] Initial Conditions Quark-Gluon Plasma Hadronization BULK (pT~T) Microscopic Mechanism Matters! CGC (x<<1) Gluon saturation Heavy Quarks (mq>>T,LQCD) [Becattini] [Blume] MINIJETS (pT>>T,LQCD) [Albacete] [Bruna] [Arnaldi] • Initial Condition–“exotic” non equilibrium CGC • Bulk –Hydrodynamics BUT finite viscosities (h,z) • Minijets–perturbative QCD BUT strong Jet-Bulk “talk” • Heavy Quarks–Brownian motion (?) BUT strongly dragged by the Bulk • Quarkonia– Are suppressed (only resonances?) or regenerated • Hadronization– Microscopic mechanism can modify QGP observables

  22. LHC RHIC • Dominance of QGP phase (tQGP> 10 fm/c) • Vanishing hadronic contamination? • A new QGP phase: perturbative plasma? • Larger h/s we get close to the pQCD estimates? Hopefully with several other surprises… Enjoy the School! • Very large yield of heavy quark (mq>>T) and jets (pT>>T) • Increasing relevance of non-equilibrated “objects”! • Existence of a primordial non-equilibrium phase • Color Glass Condensate (CGC) as high-energy limit of QCD?

  23. z y x py px Collective Expansion of the Bulk v2/e measures efficiency in converting the eccentricity from Coordinate to Momentum space h/sviscosity c2s=dP/de - EoS For the first time close to ideal Hydrodynamics The fluid with lowest ever observed h/s RHIC SPS Viscosity h/s QGP Transverse Density [fm-2]

  24. Color Glass Condensate initial conditions? dN/d2pT pT Qsat(s) Parton distr. funct Ideal Sketch At RHIC Q2~ 2 GeV2 At LHC Q2~ ? At small x (pT) dense gluon matter Gluons of small x (pT) -> larger size >1/Qs overlap and the gluon dostribution stops growing What is the impact of a different intial condition?

  25. near y x Medium away  Jet Quenching Jet triggered angular correl. Suppression of minijets 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?

  26. Heavy Quarks dragged by the medium? • - mc,b >> LQCDproduced by pQCD processes (out of equil.) • - t0 << tQGP they go through all the QGP lifetime • mc,b >> T0 no thermal production • A better test of pQCD scattering and energy loss: • - mQ>>mq small drag from the bulk Indirect measurement from semileptonic decay (D->Ken) came as a surprise: Strong suppression Large elliptic Flow

  27. Quarkonia Suppression? QQ Quarkonium dissoved by charge screening: Thermometer cc, J/Y, cb, 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. Hadronization Modified Baryon/Mesons Quark number scaling Au+Au Baryon Meson p+p PHENIX, PRL89(2003) Use medium and not vacuum -> Quark coalescence More easy to produce baryons! Hadronization is modified Dynamical quarks are visible Fries-Greco-Sorensen - Ann. Rev. Part. Sci. 58, 177 (2008)

  29. Hadronization Modified Enhancement of v2 v2q fitted from v2p GKL Baryon/Mesons Quark number scaling Au+Au p+p PHENIX, PRL89(2003) Coalescence scaling Dynamical quarks are visible Collective flows

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