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Introduction to Ultrarelativistic Nucleus-Nucleus Collisions Lecture 2

Introduction to Ultrarelativistic Nucleus-Nucleus Collisions Lecture 2. Federico Antinori (INFN Padova & CERN). Contents. Yesterday Part 1: The QGP and A-A collisions Two puzzles in QCD Confinement and deconfinement (an “intuitive” view) Nucleus-Nucleus collisions

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Introduction to Ultrarelativistic Nucleus-Nucleus Collisions Lecture 2

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  1. Introduction to Ultrarelativistic Nucleus-Nucleus Collisions Lecture 2 Federico Antinori (INFN Padova & CERN)

  2. Contents Yesterday Part 1: The QGP and A-A collisions • Two puzzles in QCD • Confinement and deconfinement (an “intuitive” view) • Nucleus-Nucleus collisions Part 2: SPS and RHIC results • Bulk particle production • Strangeness enhancement • High pT suppression Today • Part 2 cont’d: SPS and RHIC results • Recombination • Elliptic flow • Quarkonium suppression • Part 3: Hard Probes and the LHC • Heavy Ions in the LHC • LHC physics, with two examples • Quarkonia • Heavy Flavours F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  3. Recombination F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  4. Baryon puzzle @ RHIC • Central Au-Au: as many p- (K-) as p (L) at pT ~ 1.5  2.5 GeV • e+e-jet (SLD) • very few baryons from fragmentation! p K p H.Huang @ SQM 2004 F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  5. Rcp • strange particles come to rescue! • if loss is partonic, shouldn’t it affect p and p in the same way? F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  6. Quark Recombination K+ s s s s s s s s d d u u d X- u p- u d d d d d d d d d d d s u u u u u u u u s s u d d d d p+ u u s u u u u p u u d d d s W+ u s s u u d d u s d L • if hadrons are formed by recombination, features of the parton spectrum are shifted to higher pT in the hadron spectrum, in a different way for mesons and baryons  constituent quark counting S.Bass @ SQM`04 F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  7. Elliptic flow F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  8. Elliptic Flow • Non-central collisions are azimuthally asymmetric • The transfer of this asymmetry to momentum space provides a measure of the strength of collective phenomena • Large mean free path • particles stream out isotropically, no memory of the asymmetry • extreme: ideal gas (infinite mean free path) • Small mean free path • larger density gradient -> larger pressure gradient -> larger momentum • extreme: ideal liquid (zero mean free path, hydrodynamic limit) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  9. Azimuthal Asymmetry • at low pT: azimuthal asymmetry as large as expected at hydro limit! • “perfect liquid”? • very far from “ideal gas” picture of plasma F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  10. elliptic flow v2 STAR Preliminary • Recombination also offers an explanation for v2 baryon puzzle... scaled with n(quarks) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  11. Where should recombination work? • Proponents say @ pT between 1 and 4 GeV (6 GeV) for mesons (baryons) • hydrodynamics below, fragmentation above (at RHIC energy) fragmenting parton: ph = z p, z<1 recombining partons: p1+p2=ph R.Fries @ QM`04 F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  12. Quarkonia

  13. Charmonium suppression • QGP signature proposed by Matsui and Satz, 1986 • In the plasma phase the interaction potential is expected to be screened beyond the Debye length lD (analogous to e.m. Debye screening): • Charmonium (cc) and bottonium (bb) states with r > lD will not bind; their production will be suppressed For T ~ 200 MeV: lD ~ 0.1 – 0.2 fm F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  14. lD , and therefore which onium states will be suppressed, depends on the temperature: • as long as the probability of later combining an uncorrelated QQ pair at the hadronization stage is negligible, as it is at the SPS, the only chance of producing a QQ bound state is shortly after the pair is produced, while the two quarks are still correlated in phase space. Debye screening allows the two quarks to “forget” about each other’s existence, and to loose the correlation. F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  15. Nuclear absorption • There is a “normal” suppression of the production of J/y, observed already in pA and lighter ion collisions and attributed to nuclear absorpion • The Pb-Pb point falls below the nuclear absorption curve (“anomalous” suppression) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  16. Anomalous J/y suppression • J/y normalized to Drell-Yan as a function of the transverse energy (i.e. centrality) • The data points deviate from the solid curve, which indicates the prediction for nuclear absorption • The deviation increases with increasing collision centrality F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  17. J/y suppression pattern • measured/expected J/y suppression vs estimated energy density • anomalous suppression sets in at e ~ 2.3 GeV/fm3 (b ~ 8 fm) • effect seems to accelerate at e ~ 3 GeV/fm3 (b ~ 3.6 fm) • this pattern has been interpreted as successive melting of the cc and of the J/y F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  18. J/ψ ~ as suppressed as at SPS (NA50) J/ψ suppression at RHIC [Hugo Pereira (PHENIX), QM05] F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  19. all models reproducing magnitude of J/ψ suppression at SPS predicted larger suppression at RHIC J/ψ suppression at RHIC [Hugo Pereira (PHENIX), QM05] F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  20. Models including recombination do better… J/ψ suppression at RHIC [Hugo Pereira (PHENIX), QM05] F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  21. J/ψ: RAA at large rapidity NA50 at SPS (0<y<1) PHENIX at RHIC (|y|<0.35) PHENIX at RHIC (1.2<|y|<2.2) • Larger suppression at larger rapidity • What controls suppression? • energy density? • …? • The LHC should tell • see later… F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  22. Plus… • enhanced dilepton production • direct photon emission • conical emission • at low pT opposite to high pT particle • “the ridge” • wide structure in rapidity on same side of high pT particle • “the horn” • sharp peak in K+/π+ ratio as a function of s • evidence for parton saturation effects • … and many more… (next time…) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  23. Part 3: Hard Probes and the LHC F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  24. Heavy Ions in the LHC

  25. LHC as a HI accelerator • Fully ionised 208Pb nucleus accelerated in LHC (configuration magnetically identical to that for pp) • the relevant figure is s per nucleon-nucleon collision: sNN • … of course, real life is more complicated… • ion collimation • sensitivity of LHC instrumentation • injection chain • … F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  26. Luminosity limitations • Bound-Free Pair Production (BFPP): with subsequent loss of the 208Pb81+ • creates a small beam of 208Pb81+, with an intensity  Luminosity • impinging on a superconducting dipole (that you don’t want to quench…) • cross section  Z7 (!) ~ 280 b for PbPb at LHC (hadronic cross section ~ 8 b…) • Collimation losses • collimation for ions (which can break up into fragments) is harder than for protons • limitation on the total intensity • luminosity limited to ~ 1027 cm-2s-1 F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  27. Pb nuclei in the LHC • “Nominal” configuration: • 592 bunches (for protons: 2808) • 7 107 ions/bunch (for protons: ~ 1011) • L ~ 1027 cm-2s-1 (for protons: 1034 cm-2s-1 ) • 8 kHz interaction rate • “Early scheme” configuration: • for run expected at the end of first proton run • 62 bunches • 7 107 ions/bunch • L ~ 5 1025 cm-2s-1 • 400 Hz interaction rate • a dedicated AA experiment: ALICE (+ AA capability in ATLAS and CMS) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  28. LHC physics, with two examplesQuarkoniaHeavy Flavours F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  29. Why high energy? • large ε deeper in deconfinement region  closer to “ideal” behaviour? • large cross section for “hard probes” !  a whole new set of tools to probe the medium • access to low-x physics • saturation • Colour-Glass Condensate • … F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  30. Probing the medium at the LHC Pb Pb b b b b • Soft observables • multiplicity, strangeness, mT distrib., v2, interferometry, resonances, …  global event characterisation • energy density, temperatures, system size & lifetimes, viscosity, … • Hard observables  probe the medium properties! • e.g.: F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  31. ALICE Set-up Size: 16 x 16 x 26 m3 Weight: 10,000 tonnes TOF TRD HMPID ITS PMD Muon Arm PHOS TPC

  32. Quarkonia at the LHC F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  33. J/ψ@ LHC ? RHIC SPS LHC • at LHC we should finally be able to tell... • present status: more cc  reco dominates? F.Karsch et al.: PLB637 75 (2006) larger e J/y finally melts? Important: very large bb cross section @ LHC; expect 20-30% J/y originating in B decays • open b measurement! • very similar suppression at RHIC and SPS... • J/y melting compensated by cc recombination? • or maybe only y’and cc melt? F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  34. Quarkonia to dimuons in ALICE • 1 month Pb-Pb PbPb cent, 0 fm<b<3 fm Expected yields • J/y high statistics: 0-20 GeV/c • y’ lower significance • (1S) & (2S) : 0-8 GeV/c • (3S) ok, but 2-3 runs needed F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  35. Quarkonia Suppression J/ψ, , ’:Excellent sensitivity to different suppression scenarios ’’:Needs 2-3 years of high luminosity ψ’: Will be very difficult F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  36. Quarkonia in CMS • Very good performance expected for the  family • expected in nominal Pb-Pb run: • ~ 25000  • ~ 7000 ’ • ~ 4000 ’’ F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  37. Probing the medium with c & b

  38. Charm and beauty: ideal probes • study medium with probes of known colour charge and mass • e.g.: energy loss by gluon radiation expected to be: • parton-specific: stronger for gluons than quarks (colour charge) • flavour-specific: stronger for lighter than for heavier quarks (dead-cone effect) • study effect of medium on fragmentation (no extra production of c, b at hadronization) • independent string fragmentation vs recombination • e.g.: D+s/D+ • + measurement important for quarkonium physics • open QQ production natural normalization for quarkonium studies • B meson decays non negligible source of non-prompt J/y F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  39. Heavy flavour production in AA • binary scaling: can be broken by: • initial state effects (modified PDFs) • shadowing • kT broadening • gluon saturation (colour glass) (concentrated at lower pT) • final state effects (modified fragmentation) • parton energy loss • violations of independent fragmentation (e.g. quark recombination) (at higher pT) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  40. What do we know from lower energies? F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  41. Excess production at the SPS? centralcollisions M (GeV/c2) • Intermediate mass dimuon excess in central Pb-Pb at SPS (NA50) • Main known sources in that region: Drell-Yan and charm pairs F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  42. Study of the I.M. excess in NA60 H.Woehri and C.Lourenco, Phys.Rep. 433 (2006) 127-180 NA60 6500 A, 2match < 3 • Fit weighted impact parameter distribution • prompt from J/ψ dimuons, charm from PYTHIA • requires > 2 x expected D-Y to fit data • sensitivity to assumption on cc pT, Δφ • extracted value of cc cross section ~ 2 – 3 larger than extrap. • but compatible with extrapolation from NA50 p-A F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  43. Excess production at the SPS? centralcollisions M (GeV/c2) • Intermediate mass dimuon excess in central Pb-Pb at SPS (NA50) • Main known sources in that region: Drell-Yan and charm pairs No! F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  44. RHIC: “non-photonic” electrons • Identified electron spectra • STAR: dE/dx in TPC + TOF at low pT, EMC at high pT • PHENIX: combined RICH and E/p (with E from EM cal) • Rejection of non-heavy-flavour electrons • Main source of electrons: “photonic” • g e+e- conversions • Dalitz decays p0 e+e-g • Dalitz decays h e+e-g • STAR: • rejected by full invariant mass analysis of e+e- combinations • PHENIX: • estimated by simulation and subtracted (“cocktail method”) • measured by “converter method” and subtracted • Other sources of non-charm electrons: • w, r, j, K decays • estimated by sim. and subtracted (in both STAR and PHENIX) (“internal conversions”) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  45. Non-Photonic Electrons’ RAA • seem to be ~ as suppressed as charged hadrons F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  46. Words of caution… in pp … and in AuAu • non-photonic electrons: very indirect measurement • PHENIX – STAR discrepancy on absolute values of cross sections • discrepancy ~ cancels out in RAA! let’s forget about this for a moment, and take the results at face value  F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  47. Theoretically... Energy loss for heavy flavours is expected to be reduced: i) Casimir factor • light hadrons originate from a mixture of gluon and quark jets, heavy flavoured hadrons originate from quark jets • CR is 4/3 for quarks, 3 for gluons ii) dead-cone effect • gluon radiation expected to be suppressed for q < MQ/EQ [Dokshitzer & Karzeev,Phys. Lett. B519 (2001) 199] [Armesto et al., Phys. Rev. D69 (2004) 114003] average energy loss distance travelled in the medium Casimir coupling factor transport coefficient of the medium  R.Baier et al., Nucl. Phys. B483 (1997) 291 (“BDMPS”) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  48. Experimentally... • non ph. el. ~ as suppressed as light hadrons • use of high density (qhat), introduction of elastic (in addition to radiative) energy loss... not enough • high qhat and no beauty electrons does better [B.I. Abelev et al (STAR): nucl-ex/0607012] F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  49. How much beauty? [M. Cacciari et al.: PRL 95 (2005) 122001] • high pT region expected to be beauty-dominated • but how “high”? [A. Suaide QM06] • not easy to disentangle c/b contributions to RHIC non ph. el. samples (no heavy flavour vertex detectors in RHIC experiments) F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

  50. Vertex Detectors! • need less indirect measurement • full reconstruction of charm decays! • get rid of b/c ambiguities • study relative abundances in charm sector • Silicon Pixels in ALICE (+ ATLAS, CMS) • Silicon Vertex upgrades in STAR, PHENIX F Antinori, CERN-Fermilab HCP Summer School, 8-17 June 2009

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