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 pT suppression Identified particles Strangeness enhancement Quarkonia Jets Heavy Flavours Conclusions Federico Antinori – 科大 – 2012年3月29号

Introduction

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

Lattice QCD in lattice QCD, non-perturbative problems are treated by discretization on a space-time lattice  cure ultraviolet divergences 3 flavours; (q-q)=0 zero baryon density, 3 flavours e changes rapidly around Tc Tc = 170 MeV:  ec = 0.6 GeV/fm3 at T~1.2 Tc e 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

QCD phase diagram ec ~ 1 GeV/fm3 Tc ~ 170 MeV r ~ 5 - 10 nuclear Quark-Gluon Plasma Hadron gas Nuclear matter Neutron Star SPS AGS Early Universe LHC RHIC Baryon density Temperature ec ~ 1 GeV/fm3 ~ 10 ms after Big Bang Federico Antinori – 科大 – 2012年3月29号

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 b 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 peripheral central Federico Antinori – 科大 – 2012年3月29号

Multiplicity

Particle multiplicity for the most central collisions: ~ 1600 charged particles per unit of η ALICE: PRL105 (2010) 252301 log extrapolation fails (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 – 科大 – 2012年3月29号

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

Correlations

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

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

Structures in (Δη,Δφ) two shoulders near side jet peak 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

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

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

High pT suppression

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

Suppression vs event plane Alexandru Dobrin – ALICE (QM2011) significant effect, even at 20 GeV! further constraints to energy loss models  path-length dependence of energy loss (L2, L3, …) Federico Antinori – 科大 – 2012年3月29号

Identified particles

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

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

Strangeness enhancement

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

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

Quarkonia

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

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

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

Jets

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

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

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

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

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

Heavy Flavours

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

Andrea Dainese – ALICE (QM 2011) D vs π charm ~ as suppressed as pions maybe a hint of RAAD > RAAπ at low pT … 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  to be continued with higher statistics… Federico Antinori – 科大 – 2012年3月29号

Chiara Bianchin – ALICE (SQM 2011) 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

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

谢谢！