4 Strangeness at the CERN-SPS Strangeness enhancement as a signature of QGP formationIf T > TC ≈ ms, expect copious thermal s-quark production.Gluon fusion shown to dominate over light quark annihilation.Enhancement is measured relative to proton-proton collisions.NA35/NA49WA97NA57
5 Statistical/thermal models Hadrons are produced statistically – enhancement explained?CERN-ppCERN-AARHIC–AAstrangenesssSTARChemical freezeout temperature Tchnet-baryon density BStrangeness saturation factornet-strangeness density S = 0
6 Soft versus Hard QCD The advantage of high energy colliders , K, N, …, K, N, …fHadron gass = 1?(H)QGPLight-cone trajectory(Q)s = 0.4Parton formation and thermalisation0 = qzSoft processe.g. strangenessHard processe.g. jets, charmAASoft processes occur over the lifetime of the system.Hard processes occur at early times and serve as a “standard candle”.
7 High pT particle production High pT jets are well described by perturbative QCDheavy nucleusradiatedgluonskey prediction: jets are quenchedX.-N. Wang and M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480Jet of high pT hadronsFragmentationLeading hadronpTpLpTOTParton distribution functions– initial stateHard scattering cross-section– pQCD calculableFragmentation function– final state
8 High-pT hadrons in A+A collisions CentralSTAR: Phys. Rev. Lett. 89 (2002)STARCentralPeripheralPeripheralbinary collisionsscale factorp+p reference
9 Measuring jets by two-particle correlations STAR8 < pT(trigger) < 15 GeV/cSTAR: Phys. Rev. Lett. 97 (2006)DfTrigger particleAssociated (near-side)Associated (away-side)
10 Away side broadening or quenching? Measure “jet” yields as a function of zT = pT(assoc)/pT(trig)STAR: Phys. Rev. Lett. 97 (2006)STARNear-sideAway-side|| < 0.63|| < 0.63Suppression by factor 4-5 in central Au+Au.No suppression
12 2-d ( correlations In vacuo (pp)fragmentationstatic mediumbroadeningflowing mediumanisotropic shape(Armesto et al, PRL 93, (2004); Eur. Phys. J. C )d+AuAu+AuDhDhDfAway-sideDfAway-sideNear-sideNear-sideDisappearance of away-side correlation = jet quenching.Modification of near-side correlation = coupling of jet to the medium?
13 Extracting near-side “jet” yields Au+Au 20-30%3 < pT,trig. < 4 GeV/c and pT,assoc. > 2 GeV/cyield,)STAR1Ridge yield-1Jet yield-22 ()NpartBirmingham analysis: particle-type composition of the jet/ridge.Strange particles now being used as a diagnostic tool.
14 Access to a wide range of observables in one experiment! ALICE at the LHCAccess to a wide range of observables in one experiment!ITSLow pt trackingVertexingTPCTracking, dEdxTRDElectron IDTOFPIDHMPIDPID high ptPHOSg,p0MUONm-pairsPMDg multiplicity
15 UK–ALICE Birmingham’s role in ALICE ALICE trigger The ALICE central trigger system.Only major subsystem which is the responsibility of a single university group.Strong involvement in the science (Physics Performance Reports).Now one of the largest university groups in ALICE.ALICE triggerUp to 60 inputs (every 25 ns)24 L0 – 1.6 s (100 ns decision time)24 L1 – 6 s12 L2 – 90 s50 trigger classes / 6 detector clustersPb-Pb collisions: 8 kHz interaction ratep-p collisions: 200 kHz interaction rateDavid Evans / ALICE trigger
16 ALICE - Key PhysicsStudy QCD on its natural (energy) scale T > TC ≈ QCD.Explore quark and gluon dynamics in a hot medium.Hot topics:Collective behaviour – sQGP.Opacity to jets – gluon density.Heavy flavour production – Debye screening.Some new theoretical developments:AdS/CFT correspondanceConnection between string theory and ...… strongly-coupled gauge theories.Provides an alternative to (lattice) QCD.Some (limited) success so far.l+jetspl–ccg*pgbbKpp
17 New ideas in Hadronization David d'Enterria (CERN)David Evans (Birmingham)Nick Evans (Southampton)Nigel Glover (IPPP)Peter Jones (Birmingham)Frank Krauss (IPPP)Kasper Peeters (MPI)Marija Zamaklar (Durham)
18 ALICE – pp physics ALICE has a competitive programme of pp physics Precision measurements of inelastic cross-sections.Particle production as a function of pT.Test of QCD calculations.Study of diffractive events.Probes nucleon structure.Advantages of ALICELow transverse momentum coverage.Particle tracking.Particle identification.More speculative …Multiplicity: pp (LHC) = CuCu (RHIC)QGP in pp collisions?p + p 0 + XSTAR
19 UK–ALICE Physics First physics Correction for trigger biases Multiplicity and transverse momentum distributions.Initial tests of QCD; input to fragmentation functions.Are parton distributions sufficiently well understood?Correction for trigger biasesImportant for all papers reporting cross-sections (All).Longer term proton-proton physics – Pb-Pb physicsResonances – sensitive to hadronic phase (Villalobos-Baillie).Charmonium ( J/) production – Debye screening (Lazzeroni).High-pT and jet physics – energy loss (Barnby, Bombara, Evans, Lietava).Anomalous high multiplicity pp events? – (Jones).
20 Outlook and Summary Unclear whether there will be a Pb-run in 2009. From 2010, expect 1 month of Pb per year.First few years, Pb-Pb 5.5 TeV per nucleon.Option of changing beam species/energy in subsequent years.e.g. p-Pb, symmetric light ions, lower energy(ies).LHC will achieve first collisions in March 2009.ALICE has a full physics programme.UK is helping to shape that programme.First physics proton-proton collisions Pb-Pb collisions.
21 The nuclear phase diagram early universeLocation of critical point uncertain:F. Karsch, BNL Workshop, 9-10 March 2006.Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050C. R. Alton et al., Phys. Rev. D71 (2005)R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005)T0 ≈ 4-5 Tc (LHC)20025015010050T0 ≤ 2Tc (RHIC)Chemical Temperature Tch [MeV]critical point?quark-gluon plasmaSPSLattice QCDAGSdeconfinementchiral restorationhadron gasSISchemical freeze-out curveneutron starsatomic nuclei20040060080010001200Baryonic Potential B [MeV]
22 Expectations from lattice QCD F Karsch: Quark Gluon Plasma 3 (World Scientific)Central Au+Au √sNN = 200 GeVRHICLHC ?Energy density at RHICRHIC: T0/Tc = 1.5–2.0LHC: T0/Tc = 3.0–4.0J D Bjorken: Phys. Rev. D 27 (1983) 40RHIC and LHC permit a detailed study of the high T phase of QCD
23 Origin of surviving jets Surface biasRAA sets a lower bound on the densityWicks, Horowitz, Djordjevic and Gyulassy, nucl-th/Origin of surviving jets(pT = 15 GeV/c)More penetrating probes needed to explore the medium.
24 Models of energy loss Initial ideas based on collisional energy loss. J D Bjorken, FERMILAB-Pub-82/59-THYRadiative energy loss was found to be dominant for light quarks.Soft gluon emission suppressed (Landau, Pomeranchuk, Midgal effect).Energy loss is independent of parton energy, E,and becomes a function of the path length L in the medium.Two example approaches (others exist)Few hard(er) interactionsMultiple soft interactionsGLV formalismBDMPS formalismOpacity (twist) expansionStatic mediumTransport coefficientFor 1-d longitudinal expansion:Guylassy, Levai, Vitev,Wang, Wang, …Baier, Dokshitzer, Mueller, Peigne, Schiff,Salgado, Wiedemann, …
25 Use RAA to determine the medium density Nuclear modification factor, RAA, for pionsEskola, Honkanen, Salgado, Wiedemann (2004)The medium is dense (30-50 x normal matter), but RAA provides limited sensitivity.
26 ALICE – Observables ALICE is a general purpose detector Access to a wide range of observables in one experiment!