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Latest Results from the LHC: Heavy-Ion Physics

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  1. Latest Results from the LHC: Heavy-Ion Physics Jan Fiete Grosse-OetringhausCERN 2nd August 2011, CERN

  2. Contents I would like to give credit to many EPS speakers from which I took slides, in particular Federico Antinori Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Introduction • Selection of recent heavy-ion physics results on • Particle multiplicity • Correlations • Identified particles • High pT suppression • Heavy flavours • Quarkonia • Jets

  3. Introduction Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  4. Ultrarelativistic A-A Collisions • Basic idea: compress large amount of energy in a very small volume Produce a “fireball” of hot matter • Temperature: O(1012 K) • ~ 105 times T at centre of Sun • ~ T of universe about 10 µs after the Big Bang • How does matter behave under such extreme conditions? • Study the fireball properties • QCD predicts state of deconfined quarks and gluons (Quark-Gluon Plasma) • LHC can accelerate ions (up to Pb) up to ÖsNN = 5.5 TeV Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  5. Geometry of a Pb-Pb Collision Central collisions Smallimpact parameter b High number ofparticipants high multiplicity Peripheral collisions Largeimpact parameter b Low number ofparticipants low multiplicity For example: sum of the amplitudes in the ALICE V0 scintillators Reproduced by Glauber model fit Random relative position of nuclei in transverse plane Woods-Saxon distribution inside nucleus Deviation at very low amplitude expected due to non-nuclear (electromagnetic) processes b peripheral central Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  6. Multiplicity Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  7. Particle Multiplicity • For the 5% most central collisions: • 1584 ± 80 (syst) charged particles per unit of η (|η|<0.5) • 2 dNch/dη / <Npart> = 8.3 ± 0.4 (syst) • 2.2 x central Au+Au (√sNN=0.2 TeV) 1.9 x pp (NSD) (√sNN=2.36 TeV) • log extrapolationfails (finally!) ALICE: PRL105 (2010) 252301 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  8. Centrality Dependence ALICE: PRL 106 (2011) 032301 Helena Santos - ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Model comparisons • DPMJET (with string fusion) • HIJING 2.0 (no quenching) • Centrality-dependent gluon shadowing • Tuned to multiplicity in 0-5% • Saturation models (sometimes too much?) • Very similar centrality dependence at LHC & RHIC • Once corrected for difference in absolute values

  9. Correlations Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  10. Azimuthal Asymmetry • Why is it important? • Non-central collisions are asymmetric in azimuth • 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) •  Quantified by second coefficient (v2) of Fourier expansion of azimuthal distribution Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  11. Elliptic Flow v2 v2 still large at the LHC System still behaves very close to ideal liquid (low viscosity) v2(pT) very similar at LHC and RHIC  Similar hydrodynamical behaviour? ALICE: PRL 105 (2010) 252302 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  12. Closer Look at v2 • v2 as function of h • Evolution with h consistent with RHIC PHOBOS, 200 GeV CMS: PAS HIN-10-002 PHOBOS: PRC72,051901 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  13. Structures in (Δη,Δφ) Near-side jet peak Two shoulders on away side (at 120 and 240) called “Mach cone” Long-range structure in η on near side called “Ridge” Helena Santos – ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  14. Fluctuations and v3 Matt Luzum (QM 2011) v2 v3 v3/RP ALICE: PRL 107 (2011) 032301 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • “Ideal” shape of participants’ overlap is elliptic, then • No odd harmonics expected • Participants’ plane coincides with reaction plane • Fluctuations in initial conditions • Participants' plane  reaction plane • v3 (“triangular”) harmonic appears [B Alver & G Roland, PRC81 (2010) 054905] • Indeed v3 0 measured! • v3 has weaker centrality dependence than v2 • When calculated w.r.t. reaction plane, v3 vanishes • as expected, if due to fluctuations…

  15. Long η-range Correlations ? Andrew Adare – ALICE (QM2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • “Ultra-central” events: dramatic shape evolution in a very narrow centrality range • Double-hump structure on away-side appears on 1% most central • Visible without v2 subtraction! • First five harmonics describe shape at 10-3 level • “Ridge” and “Mach cone” • Explanations based on medium response to propagating partons were proposed at RHIC • Fourier analysis at LHC suggests natural alternative explanation in terms of hydrodynamic response to initial state fluctuations

  16. Identified Particles Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  17. pT Spectra and Hydrodynamics • Identified particle spectra modified by radial flow • Comparison to hydrodynamical predictions • (calculations by C Shen et al.: arXiv:1105.3226 [nucl-th]) • OK for π and K, but p seem to “misbehave” (less yield, flatter spectrum) p: feed-down corrected Roberto Preghenella - ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  18. v2 and Hydrodynamics Raimond Snellings ALICE (QM2010) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Comparison of identified particles v2(pT) with hydro prediction • (calculation by C Shen et al.: arXiv:1105.3226 [nucl-th])  again, protons are off…  what’s going on with the protons?

  19. High pT Suppression Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  20. Nuclear Modification Factor (RAA) • RAA: particle yield in AA relative to pp scaled with number of binary nucleon-nucleon collisions • Without modification RAA = 1 • RAA(pT) for charged particles in 0-5% centrality range • Minimum (~ 0.14) for pT ~ 6-7 GeV/c • Then slow increase at high pT • Still significant suppression at pT ~ 100 GeV/c • Essential quantitative constraint for parton energy loss models Yen-Jie Lee – CMS CMS-PAS-HIN-10-005 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  21. Suppression vs Event Plane • Assess path-length dependent quenching • Significant effect, even at 20 GeV • Further constraints to energy-loss models  Path-length dependence of energy loss Alexandru Dobrin – ALICE (QM2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  22. Jet-Yield Modification Factor IAA • Near-side of central events slightly enhanced IAA ~ 1.2  medium effects also visible for near-side • Away-side of central events suppressed: IAA ~ 0.6  expected from in-medium energy loss • Peripheral events consistent with unity JFGO - ALICE (QM 2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  23. Heavy Flavours Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  24. c and b Quenching at LHC • Study RAA of charm and beauty mesons and compare to light mesons • Parton mass and colour charge dependence of energy loss • Substantial suppression of heavy flavour production at LHC • Beauty suppressed too Diego Stocco – ALICE Catherine Silvestre – CMS [compilation: Andrea Dainese] Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  25. D vs π • Quarks expected to couple weaker than gluons • Colour factor (and other effects) • E.g. at pT ~ 8 GeV, factor ~ 2 less suppression expected for D than for light hadrons in BDMPS-ADSW • Charm suppression similar to pion suppression • Hint of RAAD > RAAπ at low pT? • To be continued with higher statistics… N Armesto et al., PRD 71 (2005) 054027 Diego Stocco – ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  26. Quarkonia Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  27. Quarkonia Suppression Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus Quark-Gluon Plasma "signature" proposed in the 80’s[T Matsui & H Satz, Phys. Lett. B 178 (1986) 416] In the plasma phase the interaction potential is expected to be screened beyond the Debye length λD (analogous to e.m. Debye screening) ccbar and bbbar pairs with radius > λD will not bind  production suppressed Critical "melting" temperature for J/ψ, ψ', , ', '' etc.

  28. Quarkonia at LHC Catherine Silvestre – CMS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  29. J/ψ at LHC: Forward y, Low pT • In 2.5 < y < 4 at LHC • Less suppression than at RHIC in 1.2 < y < 2.2 • as suppressed as at RHIC in |y| < 0.35 • pA reference needed for quantitative conclusions LHC: 2.5 < y < 4, pT > 0 (ALICE) RHIC: 1.2 < y < 2.2, pT > 0 (PHENIX) RHIC: |y| < 0.35. pT > 0 (PHENIX) Livio Bianchi – ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  30. LHC: |y| < 2.4, pT > 6.5 GeV/c prompt J/ψ (CMS)more suppressed than RHIC: |y| < 1. pT > 5 GeV/c inclusive J/ψ(STAR) LHC |y| < 2.5, pT > 3 GeV/c (ATLAS) J/ψ at LHC: Central y, High pT RCP PLB 697 (2011) 294 Catherine Silvestre – CMS Helena Santos – ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  31. (2S+3S) Suppression Yield of (2S+3S) relative to (1S) in Pb-Pb compared to pp Yen-Jie Lee – CMS arXiv:1105.4894 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  32. Jets Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  33. Di-jet Imbalance • Pb-Pb events with large di-jet imbalance observed by ATLAS & CMS  recoiling jet strongly quenched! Frank Ma - CMS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  34. Di-jet Asymmetry AJ Enhancement of asymmetric di-jets with increasing centrality measured w.r.t. pp & HIJING + PYTHIA AJ Helena Santos - ATLAS ATLAS: PRL105 (2010) 252303 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  35. Jet Nuclear Modification Factor RCP Suppression of jet production In central Pb-Pb w.r.t. binary-scaled peripheral Weak centrality dependence Helena Santos - ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  36. Di-jet Decorrelation in Δφ pT,1 > 120 GeV/c pT,2 > 50 GeV/c e.g.: Frank Ma – CMS CMS: arXiv:1102.1957 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Although significant energy loss (large AJ), no visible angular decorrelation in Δφ w.r.t. pp collisions • Quenched jets still back-to-back

  37. Quenched Energy • Measurement of missing pT w.r.t. leading jet direction • Di-jet momentum difference balanced by low pT particles (spread far out of jet cone) Yen-Jie Lee – CMS Frank Ma – CMS CMS: arXiv:1102.1957 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  38. Conclusions • Heavy-ion collisions at LHC have entered a new regime with abundant hard probes and powerful detectors • Exciting results from first short (low L) run • Comprehensive explanation of ridge and Mach cone • Anomalies in proton yields & momentum distributions • Heavy-flavour suppression challenges energy-loss models • Strong jet quenching balanced by soft particles • Precision measurements will constrain dynamics and transport properties of the medium Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  39. Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  40. Backup Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  41. QCD Phase Diagram ~ 10 ms after Big Bang LHC Early Universe RHIC Quark-Gluon Plasma Tc ~ 170 MeV SPS AGS Hadron gas Temperature Nuclear Neutron Star matter ~ 5 - 10 nuclear r Baryon density ec ~ 1 GeV/fm3 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus