Recent results from ALICE Domenico Di Bari Dipartimento

Recent results from ALICE Domenico Di Bari Dipartimento IA di Fisica and INFN for the ALICE Collaboration QCD@Work Lecce 22 -06 -2012

Outline of talk q. Brief introduction q Main results from Pb-Pb collisions (2010 -11) compared to p-p qd. Nch/d , energy density reached at LHC q. Interaction region geometry with HBT q. Identified p. T spectra q Particle correlations: v 2, v 3 vs p. T q. Parton energy loss: RAA(p. T) of identified particles

HI physics: a QCD test Lattice QCD calculations predict a phase transition from hadronic matter to the QGP state Hadron matter deconfined QGP Ideal gas: no interactions between quarks and gluons Liquid: significant interactions between quarks and gluons

HI space-time evolution with QGP

The ALICE experiment

d. Nch/d and e reached at LHC PRL 105 (2010) 252301 Central dependence at LHC similar to RHIC at LHC: 15 Ge. V/fm 3 at RHIC: 5 Ge. V/fm 3 >> c for QGP (0. 5 Ge. V/fm 3) (2. 1 factor for d. N/dy normalization from RHIC to LHC)

System geometry at LHC Two-pion Bose–Einstein correlations in central Pb–Pb collisions (HBT) to measure the space-time evolution of the system long is parallel to the beam out parallel to the pair p. T side is to long and out • Volume: (2 ) 3/2·R out. Rside. Rlong ≈ 5000 fm 3, ~ 2 RHIC • f: ~ 40% > RHIC (decoupling time of the system) from bang to hadronic freeze out

Transverse momentum Particle spectra Low p. T region (p. T < 2 Ge. V/c) ØRadial flow (mass dependence) Moderate p. T region (2<p. T<8 Ge. V/c) ØFlow peaks ØWhich mechanism (coalescence, . . . )? High p. T region (p. T > 8 Ge. V/c) ØVacuum fragmentation ?

Low p. T region ØStrong effect at LHC wrt RHIC ØSpectra consistent with hydro (T~420 Me. V) (protons are overestimated: hadronic cascade becomes important) ØK/π and p/π ratios (p. T integr. ) similar trend at RHIC and LHC

Intermediate p. T region ØRecent EPOS model calculation describes the data well: (K. Werner, ar. Xiv: 1204. 1394) (not decribed by coalescence model) ØBaryon/meson enhanced at LHC wrt. RHIC

Elliptic flow for identified particles z y x ar. Xiv: 1205. 5761 ØLHC: ~ 1. 3 v 2 (RHIC) (p. T integr. ), higher radial expansion (<p. T> increase) Øintermediate p. T : dep. on particle species Øhigh p. T : v 2 and v 3 small: hydrodinamic flow negligible

Parton energy loss in QGP Two mechanisms: Ømedium-induced gluon radiation (see pict. ) Øcollision with medium partons path length L In vacuum, gluon radiation suppressed at q < m. Q/EQ “dead cone” effect hard parton Average energy loss (BDMPS model): Q It depends on CR (casimir factor) = 4/3 for quarks 3 for gluons Medium transport coefficient gluon density and momenta ● Colour charge (Casimir factor, ΔEg>ΔEu, d, s) ● Parton mass (dead cone effect, ΔEb<ΔEc<. . ) ΔEg > ΔEc > ΔEb “suppression”: π > D > B

Unidentified charged particles: RAA Nuclear modification factor Comparison with several models n n At LHC the suppression is higher wrt RHIC Increase with centrality (max at p. T~6 -7 Ge. V/c)

Centrality dependence of RAA integrated in [p. Tmin, p. Tmax] ØSuppression increases with centrality ØAt a given <Npart>, RAA more suppressed at LHC wrt RHIC ØLHC similar wrt RHIC at same d. Nch/d

Heavy Flavour production in ALICE NEW Proton-Proton σcc ar. Xiv: 1205. 4007 σbb ar. Xiv: 1205. 5880 Expected in 1 Pb-Pb collision at √s. NN=2. 76 Te. V: ≈ 60 cc ≈ 2 bb

D mesons RAA Central rapidity D 0, D+, D* compatible ● Strong suppression in central collisions ar. Xiv: 1203. 2160

D mesons RAA Centrality dependence ar. Xiv: 1203. 2160

More on RAA Charm and beauty: no evidence of mass effects yet (dead cone, . . ) – more statistics needed ● Pions, charm and beauty RAA look similar -> see RAA ratio (right) ar. Xiv: 1203. 2160 NEW With the current uncertainties: ● Hint of R > 1 ● Color charge effect? Measurements are not yet conclusive

Elliptic flow of D mesons ØIndication for non zero D meson v 2 (3σ in 2 < p. T < 6 Ge. V/c) ØComparable with charged hadrons elliptic flow Challenge for models to describe both RAA and v 2!

Summary ØLHC is studying in details the propertis of the deconfined QGP state of matter q. Energy densities and temperatures well above the critical values to a deconfined state ØFrom RHIC to LHC, QGP behaves like a strongly interacting, almost perfect liquid system ØFirst results from ALICE are already challenge for theory and models Data from Pb-Pb (2011) represent > x 20 wrt 2010. Many more measurements with higher are coming. . . This year p-Pb run. . . other important issues. . . Thanks.

Back-up slides

Pb-Pb 2011 run statistics q 132 Mevts for physics q 8 Mevts for calibration Central and Semi. Central triggers Muon triggers

p/p Ratio in Jet and Bulk • Baryon over meson ratios differ significantly between AA and pp collisions Pb-Pb 0 -5% pp – Attributed to radial flow and coalescence/recombination • How do these ratios behave in a jet in AA collisions? • Two-particle correlations allow to disentangle the bulk from particles associated with a trigger particle • We measure the p/p ratio in the peak and the bulk Bulk I Dh Peak region Bulk II Dj (rad. ) Hadron Correlations Measured with ALICE - Jan Fiete Grosse-Oetringhaus 23

Particle Yields 1/Ntrig d. N/dp. T, assoc (c/Ge. V) • Particle yields are measured in peak and bulk region and corrected for tracking and PID efficiency • Difference of peak and bulk is the yield associated to the trigger particle + + Peak Bulk p + pbar Peak Bulk p. T, assoc (Ge. V/c) Hadron Correlations Measured with ALICE - Jan Fiete Grosse-Oetringhaus p. T, assoc (Ge. V/c) 24

• p/p ratio in the bulk is consistent with inclusive p/p ratio – NB. Inclusive ratio in 0 -5% and feeddown corrected • p/p ratio in peak - bulk is significantly smaller (p+pbar)/( ++ -) ratio p/p Ratio Bulk Peak-Bulk Pythia – Consistent with ratio from Pythia (6. 4 default tune) • No evidence for mediuminduced modification of jet fragmentation (R ~ 0. 40. 5) in this p. T regime Hadron Correlations Measured with ALICE - Jan Fiete Grosse-Oetringhaus Bulk Inclusive not feeddown corrected p. T, assoc (Ge. V/c) 25