1 / 41

Ultrarelativistic Nucleus-Nucleus Collisions at the LHC

Ultrarelativistic Nucleus-Nucleus Collisions at the LHC. Federico Antinori INFN, Padova, Italy and CERN, Geneva, Switzerland 中国合肥 - 中国科学技术大学 – 2012 年 3 月 29 号. Contents. Introduction Multiplicity Correlations High p T suppression Identified particles Strangeness enhancement

colton
Download Presentation

Ultrarelativistic Nucleus-Nucleus Collisions at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ultrarelativistic Nucleus-Nucleus Collisions at the LHC Federico Antinori INFN, Padova, Italy and CERN, Geneva, Switzerland 中国合肥 - 中国科学技术大学 –2012年3月29号

  2. Contents Introduction Multiplicity Correlations High pT suppression Identified particles Strangeness enhancement Quarkonia Jets Heavy Flavours Conclusions Federico Antinori – 科大 – 2012年3月29号

  3. Introduction

  4. Ultrarelativistic AA Collisions 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) Federico Antinori – 科大 – 2012年3月29号

  5. 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 – 科大 – 2012年3月29号

  6. ~ 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 – 科大 – 2012年3月29号

  7. 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 – 科大 – 2012年3月29号

  8. Multiplicity

  9. 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.) for the most central collisions: ~ 1600 charged particles per unit of η Federico Antinori – 科大 – 2012年3月29号

  10. Centrality dependence ALICE: PRL 106 (2011) 032301 Helena Santos – ATLAS (EPS 2011) • model comparisons • DPMJET (with string fusion) • HIJING 2.0 (no quenching) • centrality-dependent gluon shadowing • tuned to multiplicity in 0-5% • saturationmodels • very similar centrality dependence at LHC & RHIC • once corrected for difference in absolute values Federico Antinori – 科大 – 2012年3月29号

  11. Correlations

  12. 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 … 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 Federico Antinori – 科大 – 2012年3月29号

  13. 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 – 科大 – 2012年3月29号

  14. Structures in (Δη,Δφ) two shoulders on away side (at 120 and 240 ) aka “the Mach cone” near side jet peak long range structure in η on near side aka “the ridge” Federico Antinori – 科大 – 2012年3月29号

  15. Fluctuations  v3 Matt Luzum (QM 2011) v2 v3 ALICE: PRL 107 (2011) 032301 • “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… Federico Antinori – 科大 – 2012年3月29号

  16. Long-η-range correlations Andrew Adare – ALICE (QM2011) • “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 Federico Antinori – 科大 – 2012年3月29号

  17. High pT suppression

  18. Nuclear modification factor (RAA) CMS: PAS HIN-10-005 • 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! Federico Antinori – 科大 – 2012年3月29号

  19. 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 – 科大 – 2012年3月29号

  20. Identified particles

  21. pT spectra vs hydrodynamics Michele Floris – ALICE (QM2011) • 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) Federico Antinori – 科大 – 2012年3月29号

  22. v2 vs hydrodynamics Raimond Snellings ALICE (QM2011) • comparison of identified particles v2(pT) with hydro prediction • (calculation by C Shen et al.: arXiv:1105.3226 [nucl-th])  again, protons… Federico Antinori – 科大 – 2012年3月29号

  23. Strangeness enhancement

  24. Strangeness enhancement Maria Nicassio – ALICE (SQM2011) • enhancement decreases with increasing √s  strange/non-strange increases with √s in pp Federico Antinori – 科大 – 2012年3月29号

  25. Comparison with thermal model Alexander Kalweit – ALICE (SQM2011) • Reasonable grand-canonical description with Tch=164 MeV  except for p/π ! Federico Antinori – 科大 – 2012年3月29号

  26. Quarkonia

  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) CMS: PAS HIN-10-006 ATLAS: PLB 697 (2011) 294 Federico Antinori – 科大 – 2012年3月29号

  28. J/ψ @ LHC: forward y, low pT • LHC: 2.5 < y < 4, pT > 0 (ALICE) • less suppression than RHIC: 1.2 < y < 2.2, pT > 0 (PHENIX) • ~ as suppressed as RHIC: |y| < 0.35. pT > 0 (PHENIX) Federico Antinori – 科大 – 2012年3月29号

  29. Yen-Jie Lee – CMS Yen-Jie Lee – CMS (EPS-HEP 2011) Federico Antinori – 科大 – 2012年3月29号

  30. Jets

  31. Di-jet imbalance Frank Ma – CMS (EPS-HEP 2011) • Pb-Pb events with large di-jet imbalance observed by ATLAS & CMS • recoiling jet strongly quenched! Federico Antinori – 科大 – 2012年3月29号

  32. AJ • with increasing centrality: • enhancement of asymmetric di-jets • with respect to pp & HIJING + PYTHIA ATLAS: PRL105 (2010) 252303 Federico Antinori – 科大 – 2012年3月29号

  33. Di-jet Δφ CMS: arXiv:1102.1957 no visible angular decorrelation in Δφ wrt pp collisions Federico Antinori – 科大 – 2012年3月29号

  34. Jet nuclear modification factor • suppression of jet production • in central Pb-Pb wrt binary-scaled peripheral • very weak centrality dependence Helena Santos – ATLAS (EPS-HEP 2012) Federico Antinori – 科大 – 2012年3月29号

  35. Fragmentation function similar to fragmentation in vacuum? Federico Antinori – 科大 – 2012年3月29号

  36. Heavy Flavours

  37. c and b quenching @ LHC • substantial suppression of heavy flavour production • beauty, too! • study parton mass and colour charge dependence of interaction with medium! Federico Antinori – 科大 – 2012年3月29号

  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 Andrea Dainese – ALICE (QM 2011) N Armesto et al., PRD 71 (2005) 054027 Federico Antinori – 科大 – 2012年3月29号

  39. D0 elliptic flow • First direct measurement of D flow in heavy-ion collisions • Yield extracted from invariant mass spectra of Kp candidates in 2 bins of azimuthal angle relative to the event plane Chiara Bianchin – ALICE (SQM 2011) Federico Antinori – 科大 – 2012年3月29号

  40. Conclusions • 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 2010 data sample • death of ridge and Mach cone? • anomalies in proton yields & momentum distributions • pattern of jet and heavy flavour suppression  challenge to Eloss models • and the future looks bright! • ~ 150/µb delivered by LHC in 2011 • p-Pb run scheduled for 2012 • precision measurements + handle on cold nuclear matter effects • close in on dynamic and coupling properties of medium • and … look out for surprises!!! Federico Antinori – 科大 – 2012年3月29号

  41. 谢谢！

More Related