Recent Results from ALICE

Report
Recent Results from ALICE
E. Vercellin
Dipartimento di Fisica dell’Università di Torino and INFN Torino
Summary
• ALICE motivations, layout, data taking
• ALICE (Pb-Pb) results: a selection
– Global observables
– Anisotropic flow
– High-pT particles and Jets
– Heavy Flavors
– Quarkonia
Based mainly on “fresh”
results presented at the
Quark Matter conference,
held in August 2012
• Conclusions and perspectives
2
MOTIVATIONS, DETECTOR LAYOUT
AND DATA TAKING
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4
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6
Heavy Ion Collisions
Create QGP by colliding ultra-relativistic heavy ions
pre-equilibration  QGP 
hadronisation  freeze out
Accellerators: AGS, SPS, RHIC, LHC
SNN (GeV) =
5.4
19
200
2360 (5200)
7
8
Observables
Jets
Open charm, beauty
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• Diversi esperimenti, ciascuno mirato
allo studio di diverse osservabili
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12
LHC compared to SPS and RHIC
SPS
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 (310-3) 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
RHIC
LHC
Pion Production
X 2000
Y production
R. Vogt, hep-ph/0205330
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
.. all the above measurements in a
high-multiplicity environment!
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Central Barrel
2 p tracking & PID
|| < 1
ACORDE (cosmics)
VZERO scint. (centrality)
: -1.7– -3.7, 2.8–5.1
T0 (timing)
ZDC (centrality)
FMD (Nch -3.4<<5)
PMD (Ng, Nch)
ALICE detector
Muon Spectrometer
-2.5 >  > -4
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Detector:
Length: 26 meters
Height: 16 meters
Weight: 10,000 tons
Collaboration:
̴ 1200 Members
132 Institutes
36 countries
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
(charged particles)
• forward muon arm 2.4 <  < 4
– absorber, 3 Tm dipole magnet
10 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
µ arm
Particle identification in ALICE
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ALICE: main features and performance
TPC
ITS
TOF
TRD
HMPID
Central Barrel 
Forward det. 
Muon Arm & C.B. 
•
•
•
•
•
vertexing
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
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EMCal
Neutral mesons
Photon conversion
PHOS
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Identification of strange particles
Charmonium and D mesons
σJ/Ψ = (75 ± 3) MeV/c2
D+→ Kpp
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 √sNN
TeV
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
26
A couple of heavy-ion-specific aspects
CENTRALITY DETERMINATIONS AND
COULOMB INTERACTION
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VZERO, SPD and ZDCs
VZERO
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