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Relativistic Heavy Ions: the UK perspective Peter G. Jones University of Birmingham, UK NuPECC Meeting, University of Glasgow, 3-4 October 2008 STAR.

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Presentation on theme: "Relativistic Heavy Ions: the UK perspective Peter G. Jones University of Birmingham, UK NuPECC Meeting, University of Glasgow, 3-4 October 2008 STAR."— Presentation transcript:

1 Relativistic Heavy Ions: the UK perspective Peter G. Jones University of Birmingham, UK NuPECC Meeting, University of Glasgow, 3-4 October 2008 STAR

2 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 The nuclear phase diagram Baryonic Potential B [MeV] Chemical Temperature T ch [MeV] quark-gluon plasma hadron gas neutron stars early universe deconfinement chiral restoration Lattice QCD atomic nuclei Location of critical point uncertain: F. Karsch, BNL Workshop, 9-10 March Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050 C. R. Alton et al., Phys. Rev. D71 (2005) R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) critical point? GSI-SIS chemical freeze-out curve BNL-AGS CERN-SPS T 0 2T c (RHIC) T T c (LHC)

3 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 UK participation Involved since the inception of the CERN Heavy Ion programme WA85 WA94 WA85 WA94 NA36 NA49 STAR ALICE WA97 NA57 WA97 NA57 J.M. Nelson R. Zybert P.G. Jones (1992) E.G. Judd (1993) J.M. Nelson R. Zybert P.G. Jones H. Caines (1996) L. Hill (1997) T. Yates (1998) L. Barnby (1999) R. Barton (2001) J.M. Nelson P.G. Jones L. Barnby M. Lamont (2002) J. Adams (2005) L. Gaillard (2008) A. Timmins (2008) T. Burton E. Elhahuli D. Evans P.G. Jones C. Lazzeroni G.T. Jones O. Villalobos-Baillie L. Barnby R. Lietava M. Bombara A. Jusko M. Krivda Z. Matthews S. Navin R. Kour P. Petrov A. Palaha J. Kinson J.N. Carney O. Villalobos-Baillie M.F. Votruba R. Lietava A. Kirk D. Evans (1992) J.P. Davies (1995) A.C. Bayes (1995) M. Venables (1997) J. Kinson D. Evans G.T. Jones O. Villalobos-Baillie I. Bloodworth P. Jovanovic A. Jusko R. Lietava P. Norman (1999) M. Thompson (1999) R. Clarke (2004) P. Bacon (2005) S. Bull (2005) ALICE J. Kinson D. Evans G.T. Jones O. Villalobos-Baillie A. Bhasin P. Jovanovic A. Jusko R. Lietava R. Platt (2007) D. Tapia Takaki (2008) H. Scott O, 32 S 208 Pb 208 Pb, 197 Au 208 Pb

4 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Strangeness at the CERN-SPS Strangeness enhancement as a signature of QGP formation If T > T C m s, expect copious thermal s-quark production. Gluon fusion shown to dominate over light quark annihilation. Enhancement is measured relative to proton-proton collisions. NA35/NA49 WA97 NA57 WA97 NA57

5 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Statistical/thermal models Hadrons are produced statistically – enhancement explained? Chemical freezeout temperature T ch net-baryon density B Strangeness saturation factor net-strangeness density S = 0 strangeness s STAR CERN-pp CERN-AA RHIC–AA

6 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Soft versus Hard QCD The advantage of high energy colliders Hadron gas Parton formation and thermalisation z, K, N, … f ( H ) ( Q ) QGP AA 0 = q Light-cone trajectory s = 0.4 s = 1? Soft process e.g. strangeness Hard process e.g. jets, charm, K, N, … Soft processes occur over the lifetime of the system. Hard processes occur at early times and serve as a standard candle.

7 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 High p T jets are well described by perturbative QCD High p T particle production pTpT pLpL p TOT Parton distribution functions Hard scattering cross-section Fragmentation function – initial state – pQCD calculable – final state Fragmentation Leading hadron heavy nucleus radiated gluons key prediction: jets are quenched X.-N. Wang and M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480 Jet of high p T hadrons

8 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 High-p T hadrons in A+A collisions Central Peripheral STAR: Phys. Rev. Lett. 89 (2002) p+p referencescale factor Central Peripheral binary collisions STAR

9 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Measuring jets by two-particle correlations Trigger particle Associated (near-side) Associated (away-side) 8 < p T (trigger) < 15 GeV/c STAR: Phys. Rev. Lett. 97 (2006) STAR

10 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Away side broadening or quenching? Measure jet yields as a function of z T = p T (assoc)/p T (trig) Near-side Away-side No suppression | | < 0.63 Suppression by factor 4-5 in central Au+Au. STAR: Phys. Rev. Lett. 97 (2006) STAR

11 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 2-d ( correlations ~ 1 ~ 0 Trigger particle Trigger particle

12 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 2-d ( correlations d+AuAu+Au Near-side Away-side Disappearance of away-side correlation = jet quenching. Modification of near-side correlation = coupling of jet to the medium? In vacuo (pp) fragmentation static medium broadening flowing medium anisotropic shape Eur. Phys. J. C (Armesto et al, PRL 93, (2004); Eur. Phys. J. C ) Near-side Away-side

13 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 0 Extracting near-side jet yields Au+Au 20-30% yield, ) 3 2 GeV/c ( ) N part Jet yield Ridge yield STAR Birmingham analysis: particle-type composition of the jet/ridge. Strange particles now being used as a diagnostic tool.

14 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 ALICE at the LHC Access to a wide range of observables in one experiment! ITS Low p t tracking Vertexing ITS Low p t tracking Vertexing TPC Tracking, dEdx TPC Tracking, dEdx TRD Electron ID TRD Electron ID TOF PID TOF PID HMPID PID high p t HMPID PID high p t PHOS, 0 PHOS, 0 MUON -pairs MUON -pairs PMD multiplicity PMD multiplicity

15 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 UK–ALICE Birminghams role in ALICE 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 trigger Up to 60 inputs (every 25 ns) 24 L0 – 1.6 s (100 ns decision time) 24 L1 – 6 s 12 L2 – 90 s 50 trigger classes / 6 detector clusters Pb-Pb collisions: 8 kHz interaction rate p-p collisions: 200 kHz interaction rate David Evans / ALICE trigger

16 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 ALICE - Key Physics Study QCD on its natural (energy) scale T > T C 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 correspondance Connection between string theory and... … strongly-coupled gauge theories. Provides an alternative to (lattice) QCD. Some (limited) success so far. K l+l+ l–l– jets b cc b

17 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 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) 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 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 ALICE – pp physics ALICE has a competitive programme of pp physics Precision measurements of inelastic cross-sections. Particle production as a function of p T. Test of QCD calculations. Study of diffractive events. Probes nucleon structure. Advantages of ALICE Low transverse momentum coverage. Particle tracking. Particle identification. More speculative … Multiplicity: pp (LHC) = CuCu (RHIC) QGP in pp collisions? p + p 0 + X STAR

19 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 UK–ALICE Physics First physics Multiplicity and transverse momentum distributions. Initial tests of QCD; input to fragmentation functions. Are parton distributions sufficiently well understood? Correction for trigger biases Important for all papers reporting cross-sections (All). Longer term proton-proton physics – Pb-Pb physics Resonances – sensitive to hadronic phase (Villalobos-Baillie). Charmonium ( J/ ) production – Debye screening (Lazzeroni). High-p T and jet physics – energy loss (Barnby, Bombara, Evans, Lietava). Anomalous high multiplicity pp events? – (Jones).

20 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Outlook and Summary Unclear whether there will be a Pb-run in 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 ALICE has a full physics programme. UK is helping to shape that programme. First physics proton-proton collisions Pb-Pb collisions.

21 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 The nuclear phase diagram Baryonic Potential B [MeV] Chemical Temperature T ch [MeV] AGS SIS quark-gluon plasma hadron gas neutron stars early universe deconfinement chiral restoration Lattice QCD chemical freeze-out curve SPS atomic nuclei Location of critical point uncertain: F. Karsch, BNL Workshop, 9-10 March Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050 C. R. Alton et al., Phys. Rev. D71 (2005) R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) critical point? T 0 2T c (RHIC) T T c (LHC)

22 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Expectations from lattice QCD Energy density at RHIC Central Au+Au s NN = 200 GeV RHIC:T 0 /T c = 1.5–2.0 LHC:T 0 /T c = 3.0–4.0 RHIC:T 0 /T c = 1.5–2.0 LHC:T 0 /T c = 3.0–4.0 RHIC and LHC permit a detailed study of the high T phase of QCD J D Bjorken: Phys. Rev. D 27 (1983) 40 F Karsch: Quark Gluon Plasma 3 (World Scientific) RHIC LHC ?

23 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Surface bias R AA sets a lower bound on the density Wicks, Horowitz, Djordjevic and Gyulassy, nucl-th/ Origin of surviving jets (p T = 15 GeV/c) More penetrating probes needed to explore the medium.

24 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Models of energy loss Initial ideas based on collisional energy loss. Radiative 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) interactions Multiple soft interactions For 1-d longitudinal expansion: Static medium Opacity (twist) expansion Transport coefficient GLV formalismBDMPS formalism J D Bjorken, FERMILAB-Pub-82/59-THY Guylassy, Levai, Vitev, Wang, Wang, … Baier, Dokshitzer, Mueller, Peigne, Schiff, Salgado, Wiedemann, …

25 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 Use R AA to determine the medium density Nuclear modification factor, R AA, for pions The medium is dense (30-50 x normal matter), but R AA provides limited sensitivity. Eskola, Honkanen, Salgado, Wiedemann (2004)

26 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October /20 ALICE – Observables ALICE is a general purpose detector Access to a wide range of observables in one experiment!


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