Recent Results from ALICE

E. VercellinDipartimento di Fisica dell’Università di Torino and INFN Torino

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Summary

• ALICE motivations, layout, data taking• ALICE (Pb-Pb) results: a selection

– Global observables– Anisotropic flow– High-pT particles and Jets– Heavy Flavors– Quarkonia

• Conclusions and perspectives

Based mainly on “fresh” results presented at the Quark Matter conference, held in August 2012

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MOTIVATIONS, DETECTOR LAYOUT AND DATA TAKING

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Heavy Ion Collisions

pre-equilibration QGP hadronisation freeze out

Accellerators: AGS, SPS, RHIC, LHC

Create QGP by colliding ultra-relativistic heavy ions

SNN (GeV) = 5.4 19 200 2360 (5200)

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Observables

Jets

Open charm, beauty

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• Diversi esperimenti, ciascuno mirato allo studio di diverse osservabili

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LHC compared to SPS and RHICSPS RHIC LHC

√sNN (GeV) 17 200 5500

dNch/dy 500 850 1500-4000

t0QGP (fm/c) 1 0.2 0.1

T/Tc 1.1 1.9 3-4

e (GeV/fm3) 3 5 15-60

tQGP (fm/c) ≤2 2-4 ≥10

tf (fm/c) ~10 20-30 30-40

Vf(fm3) few 103 few 104 Few 105

The LHC is the ideal place to study the QGP: hotter - bigger -longer lived ~ 104 particles per event: Event by event physics

New or more important at LHC

Vanishing net baryon density (B 0)• Stronger thermal radiation (photons, dileptons)• Longer QGP lifetime

Parton dynamics has an impact on fireball expansion• High density (saturated) p.d.f. at small x (10-5)

impact on particle production• Hard processes: jets and jet quenching

30 (310-3) partons with Et>10 GeV (100 GeV) in centr. Pb-Pb• Heavy quarkonia:

Y family experimentally accessible, e high enough for melting?• Heavy flavors abundant production

100 c-cbar and few b-bbar in central Pb-Pb J/ Y enhancement ?

Hard Probes, heavy quarks and quarkonia @ LHC

Y production

RHIC LHC

R. Vogt, hep-ph/0205330

X 2000

Pion Production

ALICE physics goal

Global observables:Multiplicities, distributions

Degrees of freedom as a function of T: hadron ratios and spectra, dilepton continuum, direct photons

Early state manifestation of collective effects:elliptic flow

Energy loss of partons in quark gluon plasma: jet quenching, high pt spectra, open charm and open beauty

Study deconfinement: charmonium and bottonium spectroscopy

Study chiral symmetry restoration: neutral to charged ratios, resonance decays

Detect fluctuation phenomena - critical behavior: event-by-event particle composition, spectra

Measure the geometry of the emitting source: HBT, impact parameter via zero-degree energy flow

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.. all the above measurements in a high-multiplicity environment!

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ALICE detector

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

Collaboration: ̴ 1200 Members 132 Institutes 36 countries

ACORDE (cosmics)VZERO scint. (centrality): -1.7– -3.7, 2.8–5.1T0 (timing)ZDC (centrality)FMD (Nch -3.4<<5)PMD (Ng, Nch)

Central Barrel2 p tracking & PID|| < 1

Muon Spectrometer -2.5 > > -4

ALICE Acceptance• central barrel -0.9 < < 0.9

– 2 p tracking, PID (dE/dx, TOF, TRD)– single arm RICH (HMPID)– single arm PHOS– jet calorimeter EMCal

• forward muon arm 2.4 < < 4– absorber, 3 Tm dipole magnet10 tracking + 4 trigger chambers

• multiplicity -5.4 < < 3– including photon counting in PMD

• trigger & timing dets– 6 Zero Degree Calorimeters– T0: ring of quartz window PMT's– V0: ring of scint. Paddles

(charged particles)

µ arm

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Particle identification in ALICE

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ALICE: main features and performance

• particle identification (practically all known techniques)• excellent vertexing capability• efficient tracking – down to ~ 100 MeV/c• particle detection over a large rapidity range• quarkonia detection down to pT=0

vertexingHMPID

ITS TPC

TRD

TOF

Central Barrel

Forward det. Muon Arm & C.B.

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Photon conversion

EMCal

PHOS

Neutral mesons

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Identification of strange particles

Charmonium and D mesons

σJ/Ψ = (75 ± 3) MeV/c2

•J/y +- , -2.5<<-4.0, pt≥ 0

• J/y e+e- , -0.9<<0.9, pt≥ 0

D+→ Kpp

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ALICE Data Taking • Two heavy-ion runs at the LHC so far:

• in 2010 – commissioning and the first data taking• in 2011 – (energy scaled) above nominal luminosity!

• pp data taken at different c.m. energies in 2009-2012:• 0.9, 2.36, 2.76, 7 and 8 TeV reference for HI data and genuine pp physics

• p-Pb run foreseen in Jan-Feb 2013 (pilot run Sept. 2012)

year system energy √sNNTeV

integrated luminosity

2010 Pb – Pb 2.76 ~ 10 b-1

2011 Pb – Pb 2.76 ~ 0.1 nb-1

2013 p – Pb 5.02 ~ 30 nb-1

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CENTRALITY DETERMINATIONS AND COULOMB INTERACTION

A couple of heavy-ion-specific aspects

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VZERO, SPD and ZDCsVZERO

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