Heavy Ions Experiment Federico Antinori INFN Padova Italy

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

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

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

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 - EPS-HEP 2011 - Grenoble - 25 July 2011 5

Lattice QCD l 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 Me. V: ec = 0. 6 Ge. V/fm 3 • at T~1. 2 Tc e settles at about 80% of the Stefan-Boltzmann value for an ideal gas of q, q g (e. SB) 3 flavours; (q-q)=0 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 6

QCD phase diagram ~ 10 ms after Big Bang LHC RHIC Early Universe Quark-Gluon Plasma Temperature Tc ~ 170 Me. V SPS AGS Hadron gas Nuclear matter Baryon density Neutron Star r ~ 5 - 10 nuclear ec ~ 1 Ge. V/fm 3 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 7

Geometry of a Pb-Pb collision • central collisions – small impact parameter b – high number of participants high multiplicity • peripheral collisions b – large impact parameter b – low number of participants low multiplicity for example: sum of the amplitudes in the ALICE V 0 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

Multiplicity

Particle multiplicity for the most central collisions: ~ 1600 charged particles per unit of η ALICE: PRL 105 (2010) 252301 log extrapolation fails (finally!) 2. 2 x central Au+Au (√s. NN=0. 2 Te. V) 1. 9 x pp (NSD) (√s. NN=2. 36 Te. V) √s. NN=2. 76 Te. V Pb+Pb, 0 -5% central, |η|<0. 5 2 d. Nch/dη / <Npart> = 8. 3 0. 4 (sys. ) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 10

Centrality dependence • model comparisons ALICE: PRL 106 (2011) 032301 – DPMJET (with string fusion) – HIJING 2. 0 (no quenching) • centrality-dependent gluon shadowing • tuned to multiplicity in 0 -5% – saturation models (sometimes too much? ) Helena Santos - ATLAS • very similar centrality dependence at LHC & RHIC – once corrected for difference in absolute values Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 11

Correlations

Azimuthal asymmetry … in the transverse momentum distribution of produced particles • why is it important? • non-central collisions are asymmetric in azimuth = angle in the plane of the screen 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 (v 2) of Fourier expansion of azimuthal distribution Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 13

v 2 • v 2 still large at the LHC • v 2(p. T) very similar at LHC and RHIC system still behaves very close to ideal liquid (low viscosity) same hydrodynamical behaviour? ALICE: PRL 105 (2010) 252302 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 14

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

Fluctuations v 3 • “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 Matt Luzum (QM 2011) v 3 (“triangular”) harmonic appears [B Alver & G Roland, PRC 81 (2010) 054905] • and indeed, v 3 0 ! • v 3 has weaker centrality dependence than v 2 • when calculated wrt participants plane, v 3 vanishes v 2 v 3 – as expected, if due to fluctuations… ALICE: PRL 107 (2011) 032301 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 16

Long-η-range correlations • “ultra-central” events: dramatic shape evolution in a very narrow centrality range • double hump structure on awayside appears on 1% most central – visible without any need for v 2 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 - EPS-HEP 2011 - Grenoble - 25 July 2011 Andrew Adare – ALICE (QM 2011) 17

High p. T suppression

Nuclear modification factor (RAA) • RAA: particle yield in AA relative to pp scaled with number of binary nucleon-nucleon collisions • RAA(p. T) for charged particles produced in 0 -5% centrality range – minimum (~ 0. 14) for p. T ~ 6 -7 Ge. V/c – then slow increase at high p. T – still significant suppression at p. T ~ 100 Ge. V/c ! • essential quantitative constraint for parton energy loss models! Yen-Jie Lee – CMS: PAS HIN-10 -005 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 19

Suppression vs event plane Alexandru Dobrin – ALICE (QM 2011) • significant effect, even at 20 Ge. V! • further constraints to energy loss models path-length dependence of energy loss (L 2, L 3, …) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 20

Identified particles

p. T spectra vs hydrodynamics • comparison of identified particle spectra with hydro predictions – (calculations by C Shen et al. : ar. Xiv: 1105. 3226 [nucl-th]) OK for π and K, but p seem to “misbehave” (less yield, flatter spectrum) Roberto Preghenella - ALICE Michele Floris – ALICE (QM 2010) Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 22

v 2 vs hydrodynamics • comparison of identified particles v 2(p. T) with hydro prediction Raimond Snellings ALICE (QM 2010) – (calculation by C Shen et al. : ar. Xiv: 1105. 3226 [nucl-th]) again, protons are off… what’s going on with protons? Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 23

Quarkonia

Quarkonium suppression • 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 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 25

J/ψ @ LHC: forward y, low p. T • LHC: 2. 5 < y < 4, p. T > 0 (ALICE) less suppression than RHIC: 1. 2 < y < 2. 2, p. T > 0 (PHENIX) ~ as suppressed as RHIC: |y| < 0. 35. p. T > 0 (PHENIX) Livio Bianchi – ALICE Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 26

J/ψ @ LHC: central y, high p. T • LHC: |y| < 2. 4, p. T > 6. 5 Ge. V/c (CMS) prompt J/ψ • Catherine Silvestre – CMS: PAS HIN-10 -006 more suppressed than RHIC: |y| < 1. p. T > 5 Ge. V/c (STAR) LHC |y| < 2. 5, p. T > 3 Ge. V/c (ATLAS) Helena Santos – ATLAS: PLB 697 (2011) 294 inclusive J/ ψ Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 27

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

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

Jets

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

AJ • with increasing centrality: enhancement of asymmetric di-jets – with respect to pp & HIJING + PYTHIA Helena Santos - ATLAS: PRL 105 (2010) 252303 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 32

Di-jet Δφ • no visible angular decorrelation in Δφ wrt pp collisions e. g. : Frank Ma – CMS: ar. Xiv: 1102. 1957 Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 33

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 34

Yen-Jie Lee – CMS Frank Ma – CMS Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 CMS: ar. Xiv: 1102. 1957 35

Heavy Flavours

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

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

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 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!!! Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 39

Merci… • … 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 Xu and many others… • … à vous tous Federico Antinori - EPS-HEP 2011 - Grenoble - 25 July 2011 40