Recent results from the ALICE experiment on p-p and Pb-Pb collisions E. Scomparin (INFN Torino) for the ALICE Collaboration Introduction The ALICE experiment The first LHC Pb-Pb run Selected pp highlights Prospects and conclusions Bormio, January 23-27, th International Winter Meeting on Nuclear Physics

Introduction ALICE (A Large Heavy-Ion Collision Experiment): the dedicated heavy-ion experiment at the LHC Main focus on Pb-Pb collisions  QGP studies p-p collisions studied too (luminosity limited to a few cm -2 s -1 ) Reference for heavy-ion collision studies Genuine p-p physics From the problem…. …to the solution

Size: 16 x 26 meters Weight: 10,000 tons Detectors: 18

ALICE: specific features ALICE peculiarities among the LHC experiments Focus on PID  investigate chemical composition of the hot matter Push acceptance down to p T =0 (low material budget, low B)  many QGP-related features become more evident at low p T Sustain very high hadronic multiplicities (up to dN ch /d~810 3 )

PID performance: selected plots TPC dE/dx ITS Silicon Drift/Strip dE/dx Ω  ΛΚ TOF

Analyzed data samples SystemEnergy (TeV) TriggerAnalyzed events ∫Ldt pp7MB MUON 300M 130M 5 nb nb -1 PbPb2.76MB17M1.7 mb -1 pp2.76MB MUON 65M ~9M 1.1 nb nb Triggers MB: based on VZERO (A and C) and SPD SINGLE MUON: forward muon in coincidence with MB trigger

Focus on Pb-Pb Analysis of 2010 PbPb data well advanced. Results on: Global event features Collective expansion Strangeness and chemical composition Parton energy loss in the medium Light flavours Heavy flavours Quarkonia dissociation/regeneration in the medium Centrality estimate: standard approach PRL106 (2011) Glauber model fits Define classes corresponding to fractions of the inelastic Pb-Pb cross section See ALICE talks by: C. Perez Lara (Tue pm) S. Beole (Thu pm) A. Mischke (Thu pm)

Charged multiplicity – Energy density dN ch /d = 1584  76 (dN ch /d)/(N part /2) = 8.3  0.4 ≈ 2.1 x central AuAu at √s NN =0.2 TeV ≈ 1.9 x pp (NSD) at √s=2.36 TeV Stronger rise with √s in AA w.r.t. pp Stronger rise with √s in AA w.r.t. log extrapolation from lower energies 8 PRL105 (2010) Very similar centrality dependence at LHC & RHIC, after scaling RHIC results (x 2.1) to the multiplicity of central collisions at the LHC PRL106 (2011)

System size 9 Spatial extent of the particle emitting source extracted from interferometry of identical bosons Two-particle momentum correlations in 3 orthogonal directions -> HBT radii (R long, R side, R out ) Size: twice w.r.t. RHIC Lifetime: 40% higher w.r.t. RHIC ALICE: PLB696 (2011) 328

Identified hadron spectra 10 Combined analysis (ITS, TPC and TOF) Lines = blast-wave fits, extract Integrated yields Average p T Parameters of the system at the thermal freeze-out, T fo and  (radial flow)

Radial expansion of the system Significant change in mean p T between √s NN =200 GeV and 2.76 TeV  harder spectra For the same dN/d higher mean p T than at RHIC Common blast-wave fit to , K and p Strong radial flow: ≈0.66 for most central collisions, 10% higher than at RHIC Freeze-out temperature below 100 MeV Blast-wave fit parameters Centrality STAR pp √s=200 GeV

Hadrochemistry Relative abundances of hadron species can be described by statistical distributions (T ch,  B ) A.Andronic et al., Nucl.Phys.A772(2006) J.Cleymans et al., Phys.Rev.C73(2006) Description still not satisfactory at LHC energy Low T ch suggested by p spectra, but excluded by  and  If p excluded, T ch =164 MeV  T ch (LHC) ~ T ch (RHIC) ~ T c

Elliptic flow v 2 (LHC) ~ 1.3 v 2 (RHIC) (p T integrated) Increase consistent with increased radial expansion (higher p T ) System at LHC energy still behaves as a near-perfect fluid, not gas!

Identified particle v 2 Elliptic flow mass dependence due to large radial flow Magnitude and mass splitting predicted by viscous hydro in all centrality bins Radial flow too small from hydro, hadronic rescatterings play an important role in flow development  and K v 2 (p T ) well described, disagreement for p in central data

Charged hadron R AA R AA (p T ) for charged particles : larger suppression wrt RHIC Suppression increases with increasing centrality Minimum for p T ~ 6-7 GeV/c in all centrality classes R AA increases in the region p T >10 GeV/c Hint of flattening above 30 GeV/c Related to parton energy loss, in the BDMPS approach

Identified particle R AA Mesons vs baryons: different R AA at intermediate p T Related to baryon enhancement, observed e.g. in /K ratio At high p T (>8-10 GeV/c) R AA universality for light hadrons For hadrons containing heavy quarks, smaller suppression expected: dead cone effect, gluon radiation suppressed for <m q /E q

ALICE pp data sample >100M muon triggers (MUS) (to get >210 4 J/) >800M MB triggers (INT) >25M high-multiplicity triggers (SH1) Interaction trigger reading all detectors: SPD (min bias) or V0-A or V0-C at least one charged particle in 8 -units Single-muon trigger reading MUON, SPD, V0, FMD, ZDC : single muon, low-p T threshold, in the muon arm in coincidence with interaction trigger High Multiplicity trigger

Open charm in ALICE Analysis strategy Invariant mass analysis of fully reconstructed decay topologies displaced from the primary vertex Feed down from B (10-15 % after cuts) subtracted using FONLL Plus in PbPb hypothesis on R AA of D from B K  D+K-++D+K-++

D-meson R AA pp reference from measured D 0, D + and D* p T differential cross-sections at 7 TeV scaled to 2.76 TeV with FONLL Suppression of prompt D mesons in central (0-20%) PbPb collisions by a factor 4-5 for p T >5 GeV/c Little shadowing at high p T  suppression comes from hot matter Similar suppression for D mesons and pions Maybe a hint of R AA D > R AA π at low p T

Electrons from heavy-flavour decays Cocktail method Inclusive electron p T spectrum Electron PID from TOF+TPC TRD used in pp Subtract cocktail of known background sources e Impact parameter method (only pp for now) Track impact parameter cut to select electrons from beauty

R AA of cocktail-subtracted electrons pp reference from measured heavy flavour electrons p T differential cross-sections at 7 TeV scaled to 2.76 TeV with FONLL Analysis of pp data at 2.76 TeV ongoing (direct reference) Suppression of cocktail-subtracted electrons Factor for p T >3.5 GeV/c in the most central (0-10%) events Suppression increases with increasing centrality

Heavy-flavor decay muons Single muons at forward rapidity (-4<<-2.5) Background from primary /K decay not subtracted estimated with HIJING to be 9% in the most central class (0-10%) for p T >6 GeV/c  R CP for inclusive muons in 6<p T <10 GeV/c suppression increases with increasing centrality

J/ suppression Inclusive J/ R AA pp reference from pp data set at 2.76 TeV Contribution from B feed- down not subtracted (very small effect) J/ are suppressed with respect to pp collisions J/ R AA almost independent of centrality peripheralcentral

J/: comparison with RHIC Less suppression than at RHIC at forward rapidity: R AA (ALICE) > R AA (PHENIX, 1.2<y<2.2) Similar suppression as at RHIC at midrapidity (not for central!) R AA (ALICE) ≈ R AA (PHENIX, |y|<0.35) Caveat: cold nuclear matter effects different at RHIC and LHC  needs pPb running 24 ALICE, LHC, forward rapidity PHENIX, RHIC, mid-rapidity PHENIX, RHIC, forward rapidity

J/: comparison to models Parton transport model J/ dissociation in QGP J/ regeneration by charm quark pair recombination Feed-down from B-decays Shadowing R.Rapp, X.Zhao, NPA859(2011)114 A.Andronic et al., arXiv: P.Braun-Munzinger et al.,PLB490(2000) 196 Statistical hadronization model Screening by QGP of all J/ Charmonium production at phase boundary by statistical combination of uncorrelated c-quarks

A pp new result: J/ polarization ALICE focusses on pp results mainly as reference for PbPb On hard probes usually no competition with other LHC experiments due to smaller luminosity in ALICE Some notable exceptions, too  J/ polarization (first LHC results from ALICE, arXiv: ) Important measurement to discriminate among the different theoretical models of J/ production Long-standing puzzle with CDF results J/ polarization measured via anisotropies in the angular distributions of J/ decay products (polarization parameters    )  >0  transverse polarization,  <0  longitudinal polarization

J/ polarization results ALICE Coll., arXiv: , accepted by PRL M.Butenschoen, A.Kniehl, arXiv: First result: almost no polarization for the J/ First theoretical calculation (NLO NRQCD) compared to data: promising result, reasonable agreement with theory

Prospects, 2011 Pb-Pb data 2011 Pb-Pb data quite successful Smooth running, much higher luminosity  ~10 times more statistics (centrality and rare triggers) compared to 2010 New, exciting results expected soon! Total 2011 statistics  J/ A couple of performance plots Triggering on EMCAL

Conclusions 2011 has been (another) memorable year for ALICE ! After an already excellent start in 2010, with plenty of pp results, focus in 2011 on the analysis of the first Pb-Pb run First results Medium with >3 times higher energy density than at RHIC Abundance of hard probes Soft observables Smooth evolution of global event characteristics from RHIC to LHC energies  better constraints for existing models Move now towards precision differential measurements Pb-Pb 2011 running: success ! Work on experiment upgrades is starting Hard probes: novelties, surprises, challenges for theory Strong suppression of high p T hadrons (factor 7 at p T =7 GeV/c) Light and heavy quarks R AA similar J/ is less suppressed than at RHIC

Backup

ITS, TPC, TOF, HMPID, MUON, V0, To, FMD, PMD, ZDC (100%) TRD (7/18) EMCAL (4/10) PHOS (3/5) HLT (60%) 2010 data taking: detector configuration

Open symbols: ppbar Close symbols: pp Identified particle spectra

More on strangeness Inverse slope increases with mass s do not follow this trend (limited statistics?) has almost no increase over a factor 36 in √s (ISR  LHC)

Still on HBT radii Increase with multiplicity both in p-p and A-A, but different features

35 Analysis strategy –Require muon trigger signal to remove hadrons and low p t secondary muons –Remove residual decay muons by subtracting MC dN/dp t normalized to data at low p t Alternative method: use muon distance-of-closest-approach to primary vertex What is left are muons from charm and beauty –Apply efficiency corrections

36 D meson reconstruction Analysis strategy: invariant-mass analysis of fully- reconstructed topologies originating from displaced vertices –Build pairs/triplets/quadruplets of tracks with correct combination of charge signs and large impact parameters –Particle identification from TPC and TOF to reject background (at low pt) –Calculate the vertex (DCA point) of the decay tracks –Require good pointing of reconstructed D momentum to the primary vertex D 0  K - π + D +  K - π + π + D* +  D 0 π + D 0  K - π + π + π - D s  K - K + π + Λ c +  pK - π +

37 D0 K-+D0 K-+D0 K-+D0 K-+ Signals from 10 8 events –7 p t bins in the range 1<p t <12 GeV/c Selection based mainly on cosine of pointing angle and product of track impact parameters (d 0 K d 0  )

PID (ITS, TPC, TOF)

MonteCarlo scoreboard

Centrality vs models

High p T elliptic flow Due to path length dependence of parton energy loss

R AA – comparison with models