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E. Scapparone (INFN – Bologna, Italy)on behalf of the ALICE CollaborationMIAMI 2012Fort Lauderdale, Dec. 17, 2012

Recent results from ALICE

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~ 1300 members from both NP and HEP communities 35 Countries 132 Institutes~ 160 MCHF capital cost (+ ‘free’ magnet)

Armenia Brazil Chile China Croatia Cuba Czech Republic Denmark Egypt Finland

France

Germany

Greece

Hungary

India

Italy

Japan Mexico Netherlands

Norway Pakistan Peru

Poland

Romania

Russia

Serbia

Slovakia

South Africa

South Ko-rea

Spain Sweden

Switzerland

Thailand Turkey Ukraine

United Kingdom

United States

The ALICE Collaboration

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Detector:Length: 26 metersHeight: 16 metersWeight: 10,000 tons

Collaboration:> 1000 Members> 100 Institutes > 30 countries

THE ALICE DETECTOR

Muon Spectrometer -2.5 > h > -4

V0 scintillators: h -1.7– -3.7, 2.8–5.1

PID:SPD, TPC (dE/dX)TOF (Time of Flight)TRD (e/p)HMPID (Cherenkov)

Centrality:V0ZDC

Tracking @ | |h < 1:ITSTPCTRD

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• particle identification (practically all known techniques)• extremely low-mass tracker ~ 10% of X0

• excellent vertexing capability• efficient low-momentum tracking – down to ~ 100 MeV/c

vertexingHMPID

ITS TPC

TRD

TOF

ALICE performance

ALICE performance

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Warning: this is not an exhaustive presentation on All ALICE results, but just a talk focusing on few selected ALICE results…

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A taste of pp results at √s=2.76 Tev and √s=7 TeV

J/y yield as a function of charged-multiplicity in pp collisions at √s=7 TeV

ATLAS

LHCb

CMS

ALICE mm

ALICE e+e-

J/y : the 4 LHC experiments

J/Y accompanied by high hadronic activity.

MPI for heavy quarks ?

Hard partonic scattering shows a different trend

Phys.Lett. B712 (2012) 165

The charged particle multiplicities measured in high-multiplicity ppcollisions at LHC energies ~ same order as those measured in heavy-ion collisions at lower energies. Are their production rates in high multiplicity pp collisions already exhibiting any effect like J/ψ suppression ?

Phys.Lett.B704 (2011) 442

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First measurement of J/y polarization at LHC

M.Butenschoen, A.Kniehl, arXiv:1201.3862

• Long standing puzzle with Tevatron results

• First result at the LHC: almost no polarization for the J/

• Crucial input for tuning NRQCD parameters

(Phys. Rev. Lett. 108 (2012) 082001)

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2010 run : L ~ 7 mb -1

2011 run : L ~ 100 mb -1

Heavy ions !

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Global properties

At LHC the fireball ishotter, larger and lasts more

Photon T = 304±51 MeV ~ 1.4 x TRHIC Lifetime: +20% wrt RHIC(~ 10 fm/c)

Phys. Lett. B 696 (2011) 328

Volume ~ 2 x RHIC (R3 ~ 300 fm3)

Phys. Lett. B 696 (2011) 328

tmdy

dN

AV

E

0

1)(

Energy density ~ 3 x RHIC~ 10 GeV/fm3

PRL 105, 252301 (2010)

S. Das at QM2012

Hydro Calculation

RHIC

p

p

K

PbPb

pp

Radial flow pushes spectra depending on mass

Very strong radial flow, b ≈ 0.65 (2/3 of c!) even larger than predicted by most recent hydro

p-

Isotropic radial flow

P >> 0

P = 0

v0

v0

v0

Very significant changes in slope compared to RHIC, most dramatically for protons 10

Radial Flow- pressure P in center

drives expansion flow

velocity b=v0/c

- depends on f(P, t, EoS,)

momentum p = g m v0 =>

particles of different mass have

characteristic & different

momentum spectra

v0

v0

v0

What about Radial Flow @ LHC ?

11arXiv: 1208.1272, accepted by PRL

Fit to the data with Blast-Wave modelSchnedermann et al., PRC 48, 2462 (1993)⟨βT ⟩ = 0.65 ± 0.02

Comparison with models:VISH2+1: viscous hydrodynamicsShen et al., PRC 84, 044903 (2011),p K ok up to 1.5 GeV/c, missing p lack of

hadron phase ?HKM: hydro + UrQMD(hadron particle Cascade), Karpenko et al., arXiv:1204.5351 improved p description (hadron cascade increases radial flow)Krakow: viscous corrections, lower effective Tch, Bozek, PRC 85, 034901 (2012)

Comparing to models

Model vs data comparison suggestsa hydrodynamic interpretation of the transverse momentum spectra at the LHC.

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flow" directed" cos1 v flow" elliptic" 2cos2 v

Fourier expansion of azimuthal distribution:

Flow: Correlation between coordinate and momentum space => azimuthal asymmetry of interaction region transported to the p T

® measure 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 pathlarger density gradient -> larger pressure gradient -> larger momentum extreme: ideal liquid (zero mean free path, hydrodynamic limit)

py

Py

Px

....2cos2)cos(212)( 21

0 RPRPRP

vvN

d

dN

x

yz

Azimuthal asimmetries

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• Collective behavior observed in Pb-Pb collisions at LHC (+30% wrt v2

RHIC) ideal fluid behavior (extremely low viscosity h » 0 )

• v2 as a function of pT not dramatically different wrt RHIC (few variations for identified hadrons, predicted by hydro models - see C. Shen et al arXiv:1105.3226) v2 increase with s from hadron <pT> increase• Testing hydrodynamical evolution

central

semi-central

PRL 105, 252302 (2010), > 250 citations (INSPIRE)

v2 Measurements at the LHC

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Viscous hydrodynamic model calculations reproduce the main features of v2 atlow transverse momentum:• mass dependence is better modelled for peripheral collisions;• for central collisions overestimate baryon flow;• Adding hadronic rescattering phase (VISHNU) improves the agreement with data Heinz, Shen, Song, AIP Conf. Proc. 1441, 766 (2012)

Hydrodynamic model predictions

Hydro not ok for baryons at 10-20%centrality

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Particles

STAR, S.Shu at QM2012 NCQ scaling goodbye….

NCQ scaling: partonic dof dominant; No scaling: hadronic dof dominant

NCQ scaling holds q

uite well at

any centralities a

t low energies..

Alice: stronger NCQ violation. Stronger radialflow or Jet quenching/rescattering, more important than coalescence ?

STAR, Phys. Rev. C 77 (2008) 54901

Dat

a/fit

PHENIX Phys. Rev. C85 064914(2012)

NCQ scaling at R

HIC holds in

0-10%

Centrality bin: d

eviations st

art at ~1GeV/c

“ideal” shape of participants’ overlap is

~ elliptic; no odd harmonics expected participants’ plane coincides with event plane but fluctuations in the initial position of

the partecipant nucleons give:

- plane event plane

- v3 (“triangular”) harmonic appears

[B Alver & G Roland, PRC81 (2010) 054905]

and indeed, v3 0 !

ALICE: PRL 107 (2011) 032301

Fluctuations v3 ….(+ 3 v3 cos(3( -j y)))Sensitive to h/s

Similar v2 trend, mass ordering;

v3 has weaker centrality dependence than v2 when calculated wrt participants plane, v3 vanishes (as expected, if due to fluctuations…).

Progress in precision measurements of h/s

fluctuations discriminate & constrain models:large sensitivity to viscosity

arXiv:1205.5761v2

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- Less suppression wrt RHIC;- ALICE data flatter at high centralities: almost no centrality dependence for Npart > 100;- Evidence for c quark coalescence ?

2.5 < y < 4

1.2 < y < 2.2

J/Y in ALICE: the forward region

σ(cc)LHC ≈ 10 × σ(cc)RHIC

c

c

c

c

Colour screening @ work

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J/Y in ALICE: the pT dependence

- Nice agreement with CMS data;- Higher suppression at high pT

Predicted by coalescence model

Still uncertainties from shadowing run p-Pb coming soon

Does shadowing depends on the interaction centrality ?

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ψ’ should have a similar suppression at LHC energies wrt J/ψ (ψ’ melts at smaller T wrt J/ψ)

Tc ~ 160-170 MeVTAlice ~ 300 Mev

l ~ 0.15 fm > 0.29 fm (J/Y) > 0.56 fm (ψ’ )

ALICE not confirming CMS data(though at different rapidity)

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Hints for J/Y and D v2 ≠ 0

..hints for a strong coupling c - medium

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First pA Collision, Sep. 13th, 2012

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- Data favour models including shadowing- Saturation models predict too steep h dependence

Compatible with 1above 2-3 GeV/c→ binary scaling ispreserved, no (or small)initial state effectsNo sign ( or weak)Cronin effect

pT spectrum not reproduced by HIJING or DPMJET.Both saturation models and models with shadowing can reproduce data

p-Pb pilot run, Sep 2012

arXiv:1210.3615v1,arXiv:1210.4520v1

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Initial parton-parton scattering with large momentum transfer:

► calculable in pQCD

Particle jets follow direction of partons

Nucleus-nucleus collisions

► hard initial scattering

► scattered partons probe traversed hot and dense medium

► ‘jet tomography’

Hard Processes to Probe the Medium (Rutherford experiment...)

)(Yield

)(Yield)(

ppAACOLL

AAAA

T

TT pN

ppR

Medium modification quantified vianuclear modification factor RAA

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RAA(pT) for charged particles produced in 0-5% centrality range @ LHC:minimum for pT ~ 6-7 GeV/c then slow increase at high pTinterpreted as due to loss of energy of parton propagating through medium.A deeper inspection: selected hadrons in the medium: heavy quarks

Strong suppression for hadrons….

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Near side: compatible with PythiaBulk: p/p increase; overall baryon enhancement

Jet particle composition

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Energy loss in a dense medium proceeds mostly through gluon radiation:

- Gluon radiation higher for light quark than for heavy quark:

( dead cone: for q < MQ/EQ)

2) Gluon radiation stronger for gluons wrt quarks (higher colour charge);

Cr= 3

Summary: smaller DE expected for heavy quarks

L path in the medium

L

1)

q smaller for light quarks

..and heavy hadrons originate mostly from quark jets

Cr= 3/4 Cr= 1/2

<DE> as · Cr · q · L 2^

DEg > DEq> DEc > DEb

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Hint for smaller D0,D+,D- suppression for pt < 8 GeV/c ?

RAA for heavy flavours

ALICE: JHEP 09 (2012) 112

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New: DS !

Less suppression (s quark @ work) ?

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► Strong detector/physics efforts in view of the LHC upgrade

► Upgrade experiment to be able to run with 50 kHz Pb-Pb collision rates, several nb-1 per run (2 MHz proton-proton)

► Various new detectors being proposed (stregthen ALICE uniqueness at LHC)

ITS: B/D separation, heavy baryons, low-mass dielectrons

MFT: b-tagging for low pt J/psi and low-mass di-muons at forward y

VHMPID: New high momentum PID capabilities

FOCAL: Low-x physics with identified g/p0

The future: upgrade planning