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Heavy Ions: Experiment

Heavy Ions: Experiment. Federico Antinori (INFN Padova, Italy). A-A collisions in the LHC!. John Jowett - LHC. Contents. Introduction Selection of results (hard choices were required…) Particle multiplicity Correlations High p T suppression Identified particles Quarkonia Jets

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Heavy Ions: Experiment

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  1. Heavy Ions: Experiment Federico Antinori (INFN Padova, Italy)

  2. A-A collisions in the LHC! John Jowett - LHC Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  3. Contents • Introduction • Selection of results (hard choices were required…) • Particle multiplicity • Correlations • High pT suppression • Identified particles • Quarkonia • Jets • Heavy flavours • Conclusions

  4. Introduction

  5. Ultrarelativistic AA Collisions Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 basic idea: compress large amount of energy in a very small volume • produce a “fireball” of hot matter: temperature O(1012 K) • ~ 105 x T at centre of Sun • ~ T of universe @ ~ 10 µs after 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)

  6. Lattice QCD 3 flavours; (q-q)=0 • in lattice QCD, non-perturbative problems are treated by discretization on a space-time lattice  cure ultraviolet divergences • zero baryon density, 3 flavours • e changes rapidly around Tc • Tc = 170 MeV:  ec = 0.6 GeV/fm3 • at T~1.2 Tce settles at about 80% of the Stefan-Boltzmann value for an ideal gas of q,q g (eSB) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  7. ~ 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 QCD phase diagram Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  8. Geometry of a Pb-Pb collision • central collisions • small impact parameter b • high number of participants high multiplicity • peripheral collisions • large impact parameter b • low number of participants low multiplicity for example: sum of the amplitudes in the ALICE V0 scintillators reproduced by Glauber model fit (red): • 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 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  9. Multiplicity

  10. Particle multiplicity ALICE: PRL105 (2010) 252301 log extrapolationfails (finally!) 2.2 x central Au+Au (√sNN=0.2 TeV) 1.9 x pp (NSD) (√sNN=2.36 TeV) √sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5 2 dNch/dη / <Npart> = 8.3  0.4 (sys.) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 for the most central collisions: ~ 1600 charged particles per unit of η

  11. Centrality dependence ALICE: PRL 106 (2011) 032301 Helena Santos - ATLAS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • 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

  12. Correlations

  13. Azimuthal asymmetry • 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 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 … in the transverse momentum distribution of produced particles • why is it important? • non-central collisions are asymmetric in azimuth azimuth = angle in the plane of the screen

  14. 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  same hydrodynamical behaviour? ALICE: PRL 105 (2010) 252302 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  15. Structures in (Δη,Δφ) near side jet peak two shoulders on away side (at 120 and 240 ) aka “the Mach cone” long range structure in η on near side aka “the ridge” Helena Santos – ATLAS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  16. Fluctuations  v3 Matt Luzum (QM 2011) v2 v3 ALICE: PRL 107 (2011) 032301 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • “ideal” shape of participants’ overlap is ~ elliptic • in particular: no odd harmonics expected • participants’ plane coincides with event plane • but fluctuations in initial conditions: • participants plane  event plane • v3 (“triangular”) harmonic appears [B Alver & G Roland, PRC81 (2010) 054905] • and indeed, v3  0 ! • v3 has weaker centrality dependence than v2 • when calculated wrt participants plane, v3 vanishes • as expected, if due to fluctuations…

  17. Long-η-range correlations Andrew Adare – ALICE (QM2011) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • “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 any need for 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 of new data suggests very natural alternative explanation in terms of hydrodynamic response to initial state fluctuations

  18. High pT suppression

  19. Nuclear modification factor (RAA) Yen-Jie Lee – CMS CMS: PAS HIN-10-005 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • RAA: particle yield in AA relative to pp scaled with number of binary nucleon-nucleon collisions • RAA(pT) for charged particles produced 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!

  20. Suppression vs event plane • significant effect, even at 20 GeV! • further constraints to energy loss models  path-length dependence of energy loss (L2, L3, …) Alexandru Dobrin – ALICE (QM2011) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  21. Identified particles

  22. pT spectra vs hydrodynamics Roberto Preghenella - ALICE Michele Floris – ALICE (QM2010) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • comparison of identified particle spectra with hydro 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)

  23. v2 vs hydrodynamics Raimond Snellings ALICE (QM2010) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • 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 protons?

  24. Quarkonia

  25. Quarkonium suppression Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • 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) • cc and bb states with radius > λD will not bind  their production will be suppressed

  26. J/ψ @ LHC: forward y, low pT • LHC: 2.5 < y < 4, pT > 0 (ALICE) Livio Bianchi – ALICE Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • less suppression than RHIC: 1.2 < y < 2.2, pT > 0 (PHENIX) • ~ as suppressed as RHIC: |y| < 0.35. pT > 0 (PHENIX)

  27. J/ψ @ LHC: central y, high pT • LHC: |y| < 2.4, pT > 6.5 GeV/c (CMS) prompt J/ψ • more suppressed than RHIC: |y| < 1. pT > 5 GeV/c (STAR) inclusive J/ ψ • LHC |y| < 2.5, pT > 3 GeV/c (ATLAS) Catherine Silvestre – CMS CMS: PAS HIN-10-006 Helena Santos – ATLAS ATLAS: PLB 697 (2011) 294 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  28. Yen-Jie Lee – CMS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  29. Yen-Jie Lee – CMS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  30. Jets

  31. Di-jet imbalance Frank Ma - CMS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • Pb-Pb events with large di-jet imbalance observed by ATLAS & CMS • recoiling jet strongly quenched!

  32. AJ • with increasing centrality: • enhancement of asymmetric di-jets • with respect to pp & HIJING + PYTHIA Helena Santos - ATLAS ATLAS: PRL105 (2010) 252303 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  33. Di-jet Δφ e.g.: Frank Ma – CMS CMS: arXiv:1102.1957 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 no visible angular decorrelation in Δφ wrt pp collisions

  34. Jet nuclear modification factor • suppression of jet production • in central Pb-Pb wrt binary-scaled peripheral • very weak centrality dependence Helena Santos - ATLAS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  35. Yen-Jie Lee – CMS Frank Ma – CMS CMS: arXiv:1102.1957 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  36. Heavy Flavours

  37. c and b quenching @ LHC • substantial suppression of heavy flavour production • beauty, too! Diego Stocco – ALICE Catherine Silvestre - CMS • study parton mass and colour charge dependence of interaction with medium! Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 [compilation courtesy of Andrea Dainese]

  38. D vs π • charm ~ as suppressed as pions • maybe a hint of RAAD > RAAπ at low pT …  to be continued with higher statistics… • quarks (CR = 4/3) expected to couple weaker than gluons (CR = 3) • at pT ~ 8 GeV, factor ~ 2 less suppression expected for D than for light hadrons in BDMPS-ADSW Diego Stocco – ALICE N Armesto et al., PRD 71 (2005) 054027 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011

  39. Conclusions Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • in November 2010, the field of ultrarelativistic nuclear collisions has entered a new era with the start of heavy ion collisions at the LHC • abundance of hard probes • state-of-the art collider detectors • exciting results already from first, limited data samples • death of ridge and Mach cone? • anomalies in proton yields & momentum distributions • pattern of jet and heavy flavour suppression challenges Eloss models • the future looks very bright • precision measurements  constrain dynamic and coupling properties of medium • look out for surprises!!!

  40. Merci… Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 • … aux organisateurs for the invitation to present this plenary talk • … à: Peter Braun-Munzinger, Brian Cole, Andrea Dainese, David d’Enterria, Paolo Giubellino, Raphaël Granier de Cassagnac, Barbara Jacak, Peter Jacobs, John Jowett, Karel Šafařík, Carlos Salgado, Jürgen Schukraft, Edward Shuryak, Peter Steinberg, Xin-Nian Wang, Urs Wiedemann, Nu Xuand many others… • … à vous tous

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