WG2: Phases of Nuclear Matter

1. WG2: Phases of Nuclear Matter • Verylively meeting yesterday, first face-to-faceaftertwo EVO ones, essentiallyPhyscisdiscussions.... • Severalpresentations on key questions • In general, focus on overarchingPhysicsquestionsfromwhich derive the needsforexperimentation and theoretical work , includingcomputing • Timeline set, homeworksassigned… • Draft 0 ofsectionsbyearlyNov • 2 EVO meetings • two-dayfinalwritingsession in January • The field, whichislargelydata-driven, hasseen major developmentsince the last LRP, both in theory and experiment, and hasanambitiousplanfor the coming decade: • A vigorousexplorationof the QCD phasediagram • In the high-mBdirection • In the high-T direction • At the liquid-gasboundary • Differentmethods and approaches, with a common aim: a qualitative steptowards a descriptionofhigh-density and temperature nuclearmattercalculablefrom first principles • The listoffundamentalquestionswilldevelopthrough the work of the comingtwomonths

2. Phase diagrams Early universe quark-gluon plasma (QGP) Tc c-symmetric hadron gas c- Symmetry Broken Temperature Colour super conductor nuclei nucleon gas neutron stars r0 net baryon density

3. A few fundaments • Experimentalresultshavebeenpopulating the phasediagram • The fireball emits hadrons fron an equilibrium state • All data at the different energies are in agreement with a thermal model with 3 parameters: T, mB , V • A limiting temperature emerges as a function of c.m. energy , matching predictions from Lattice QCD for a phase limit • The fireball expands collectively like an almost ideal fluid • hydrodynamic flow characterized by azimuthal anisotropy coeffient v2 • The system has very low viscosity (close to the AdS/CFT limit) • Flow builds up at the partonic level • At high T (RHIC energies) the matterproducedisopaqueto hard probes (high-pTparticlessuppressed, opposite-side jet absorbed) • At RHIC multiplicitiesconsistentwithgluonsaturationeffects

5. Exploring the QCD phase diagram at large μB with heavy-ion collisions Physics topics and open questions: Nuclear matter equation-of-state: • What are the hydrodynamic properties and the degrees-of-freedom of nuclear matter at neutron star core densities? Hadrons in dense matter: • How are hadron properties modified in the hot and/or dense medium ? • What is the electromagnetic structure of hot and dense nuclear matter ? • Is chiral symmetry restored at high baryon densities, what are the mechanisms of hadron mass generation? Strange matter and charm physics : • Does strange matter exist in the form of heavy multi-strange objects? • How does charm propagate in hot / dense / cold nuclear matter? Exploring the phase diagram of strongly interacting matter : • Where is the phase transition between hadronic matter and partonic matter located as function of temperature and net-baryon density? • Is there a region of phase coexistence? • Are there new states of matter beyond hadrons or QGP (preformed pairs, quarkyonic matter, ...?? • Does QCD matter feature a critical endpoint? If yes, where is it located? • Do the deconfinement and the chiral phase transitions coincide?

6. Physics topics and observables The equation-of-state at high B  collective flow of hadrons  multistrangehyperonproduction at threshold energies Onset of chiral symmetry restoration at high B in-medium modifications of hadrons (,, e+e-(μ+μ-), D) Deconfinement phase transition at high B  excitation function and flow of strangeness (K, , , , )  excitation function and flow of charm (J/ψ, ψ', D0, D, c)  excitation function of low-mass lepton pairs  (dis)appearance of quark-number scaling of elliptic flow QCD critical endpoint  excitation function of event-by-event fluctuations (K/π,...)

7. Exploring the QCD phase diagram at large μB with heavy-ion collisions: the tools • RHIC energy-scan:search for QCD-CP with bulk observables • NA61@SPS: search for QCD-CP with bulk observables • MPD@NICA: search for the QCD mixed phase • CBM@FAIR: scan of the phase diagram with bulk and rare observables SPS Pb+Pb 30 A GeV Rare diagnostic probes: unique discovery potential =>probe the dense fireball (up to date only freeze-out probes have been measured in A+A collisions at 2 - 30 AGeV) Particle multiplicity x branching ratio

8. Existing and future experiments on (dense) nuclear matter physics in Europe 2010 – 2014 (?) Upgraded HADES at SIS18 (20 kHz reaction rate) Au+Au, Ag+Ag, π+A, FOPI at SIS18: K0, K+, K-, φ, Λ, production in π- on p, C, Pb @ 1.7 GeV/c, (S339, 2010), A+A ? Na61 (former NA49) at SPS p+A, S+S, In+In? 2015 - ? HADES/CBM at FAIR SIS100/300 p+p, p+A, A+A up to 45 A GeV hadrons incl. multistrange hyperons, dileptons, open and hidden charm

9. Effective models for QCD thermodynamics • Major progress in understanding EOS at finite Temperature fromcalculations on the lattice • Progress fueledbyEuropeangroups, butcomputingresourcesstillmostlyover the Atlantic • The existence and position of Critical Point (CP) is model and parameter dependent • Work defining a strategy for observation • Effective chiral models provide a powerful tool to study the critical consequences of the chiral symmetry restoration and deconfinement in QCD, however to quantify the QCD phase diagram and thermodynamics require first principle LGT calculations • Major effort of LGT working groups with Large Scale Computing for the next 5 years is necessary

10. The High-T frontier • Understand hydrodynamic properties of the Plasma and their evolution with temperature and density • Will the plasma at very high T be strongly coupled or will be understandable in terms of a gas of weakly coupled quasi-particles? • Measure confinement-related observables such as the hierarchy of quarkonium suppression. • Experiments at the LHC are the first to have access to both charmonium and bottonomium bound states and to B and D mesons to which to normalise. • To what extent can Jet Quenching be utilized for a detailed characterization of the QGP? • The LHC will be unique in extending the measurements beyond leading hadron suppression, thus increasing its sensitivity to fundamental properties of the QGP. • Gain experimental access to a qualitatively novel kinematic regime of high-density QCD, in which bulk properties are characterized by a perturbatively calculable saturation scale • Particle production in AA and pA collisions may provide strong support for the onset of saturation physics.

11. Hydrodynamic properties of the Plasma and their evolution with Temperature and density Observable: elliptic flow • RHIC data on elliptic flow are close to ideal fluid predictions • Ideal hydrodynamics is calculable from first principles, and deviations from ideal behavior are sufficiently small to be characterized by dissipative hydrodynamics (Experimental access to QCD transport coefficients and relaxation times) • Main uncertainty: intial conditions • Need accurate pA and eA data • But also: effects of hadronization • Large lever arm in going to LHC will provide a key test of present understanding • The study of transport coefficients is a model case of cross-fertilization: • Lattice QCD vc string theories • Nuclear Physics vc Physics of Cold Atoms

13. Hard Probes in Heavy Ion Collisions • Measure jet energy loss mechanisms and confinement-related observables such as the hierarchy of quarkonium suppression • extend the jet quenching measurements beyond leading hadron suppression, thus increasing its sensitivity to fundamental properties of the QGP. • Measure both charmonium and bottonomium bound states and B and D mesons to which to normalise. • Need: • large integrated luminosity (e.g. for hierarchy of quarkonium suppression) • experimentally controlled p-A and pp baselines

14. Embedding hard QCD processes in the QGP:Physics Opportunities How does this radiation depend on transport properties? How does this parton thermalize? What is the dependence on parton identity? Characterize Recoil: What is kicked in the medium?

15. The probes: • Jets • identified hadron specta • D-,B-mesons • Quarkonia • Photons • Z-boson tags The range: ,x, A, luminosity Abundant yield of hard probes + robust signal (medium sensitivity >> uncertainties) = detailed understanding of dense QCD matter Rich, as yet unexplored phenomenology at LHC Covered at RHIC

16. Large x Gluon density increases Small x The small-x nature of nuclear matter: a qualitatively novel regime of QCD • GLUON SATURATION • fromevolutionequations (DGLAP, BFKL): • gluon density increaseswith Q2 and 1/x • leads to very high gluon density • problemswithunitarity • for high density non-linearprocessesbecomeimportant • gluonsaturationbelowsaturation scale • QCD matter at small Bjorken x has the universal form of colorglasscondensate (CGC) • the CGC is perturbatively calculable More important in nuclei

17. Use Forward Hadron production to study saturation effects • Allowdirectaccesstogluondistributions • Measure: • Suppression of single hadrons: main sensitivity to reduced density fromsaturation • Suppressionofdihadrons Major jump from RHIC to LHC: possibility of using perturbative methods but need an upgrade of the detector in the Froward region

18. Theory @ the high-T frontier • Both approaches are essential: • First principle calculations of fundamental properties of the QGP and their relation to experimentally accessible probes • Finite temperature lattice QCD calculations provide a unique tool for the characterization of thermal equilibrium properties such as equation of state, spectral functions or transport coefficients of the QGP • String theory-inspired calculations using the AdS/CFT correspondence provide a rigorous tool to calculate equilibrium properties of a large class on non-Abelian Gauge theories. While these tools do not apply directly to QCD they provide fundamental insight into strongly coupled gauge theories also for dynamical questions which are very difficult to address with lattice QCD. • Modeling the dynamical evolution of Heavy-Ion collisions. (essential to link the fundamental properties of QGP to experimental observables). • Hydrodynamic simulations, applying quantitatively controlled simulations of viscous fluid dynamics to the early evolution of Heavy Ion collisions to disentangle initial conditions and hadronization from the signatures of viscous transport parameters which are calculable from first principles in QCD. • Modeling of the propagation of hard probes in the QGP. • Modeling of the dynamics of hadronization.

19. Challenges for the exploration of the Nuclear EOS in the nucleonic regime • How doesmatterinteract? • How ismatterorganized? • Fundamental for the understanding of neutron stars and SN explosions • The density dependence of the symmetry energy Strategy: compare isospin sensitive observables measured in HI collisions with transport calculations where the functional dependence of the symmetry energy can be varied • The phase structure of lowdensity NM • A unique theory for all phases (samedegrees of freedom in the different phases): easierthan QGP • Finitenuclei: laboratory for phase transitions in finitesystems • Directions: • Detectors: Isospin measurementsdemandcompleteisotopicresolution • Beams: needexotichighlyasymmetricbeams

20. g=1.5 g=0.5 g=1.0 (m1-m2)/mtot A few examples(data from European Experiments) • Reaction mechanism allows to constrain the symmetry energy • Bimodality as a generic feature of first order phase transitions in finite systems (the order parameter changes discontinuously- two solutions of similar probability) – the energy dependence allows extraction of the latent heat 40Ca+46Ti 25 A.MeV CoMD Au+Au 60 AMeV 80 AMeV 100 AMeV Au+Au 80 AMeV INDRA PRL 2009 Multics NPA 2008 (data: blue points) CHIMERA PRL 09

21. spares

22. Elliptic flow data are close to ideal fluid predictions • (experimental access to equation of state) “Almost ideal” is the ideal case to study QCD M. Luzum, P. Romatschke, PRC 78 (2008) 034915 Deviations sufficiently small to be characterized by dissipative hydrodynamics (Experimental access to QCD transport coefficients and relaxation times) • Main uncertainty: initial conditions • - constrained best by e-A • but also by p-A