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QM2004 Yves Schutz 1
Heavy-Ion Physics @ LHC
Program Detectors Observables
~1100 participants:
26 experimental contributions QM04 6 oral: P. Glaessel, V. Manzari, A. Vestbo, H. Takai, B. Wyslouch, S. Blyth. 20 posters: Spectra 23, HBT 1, High pT 17, 20, 21, Flavor 18, 19, 23, Instr. 1, 2, 7, 8, 10, 12, 14, 15, 16, 17, 22, 30.
Measure flavor content and phase-space distribution event-by-event: Most (2 * 1.8 units ) of the hadrons (dE/dx + ToF),
leptons (dE/dx, transition radiation, magnetic analysis) and photons (high resolution EM calorimetry);
Track and identify from very low (< 100 MeV/c; soft processes) up to very high pt (~100 GeV/c; hard
processes); Identify short lived particles (hyperons, D/B meson)
through secondary vertex detection; Jet identification;
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ALICE PID performancesALICE PPR CERN/LHCC 2003-049
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ALICE tracking efficiency
p/p < 1%
100%
pt (GeV/c)1 3 5
0
0.4
0.8
1.2
ALICE PPR CERN/LHCC 2003-049
TPC only
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ALICE track resolution at high pt
10 100pt (GeV/c)50
p/p
(%
)
10
30
50
ALICE PPR CERN/LHCC 2003-049
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ALICE construction status
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ALICE TPC
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ALICE Space Frame
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ALICE Dipole coil
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ALICE pixel40K channels200+150 m
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CMS
• Central tracker• High resolution EM calorimeter• Hadronic calorimeter
Superconducting solenoid magnet 4T
• Muon spectrometer
• Very forward calorimeters• ZDC• CASTOR• TOTEM
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ATLAS
Inner detector
Solenoid 2TEM calorimeter
H calorimeter
detectors
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CMS & ATLAS Experiments designed for high pt physics in
pp collisions: Precise tracking systems in a large solenoid
magnetic field; Hermetic calorimeters (EM+Hadronic)
systems with fine grain segmentation; Large acceptance muon spectrometers; Accurate measurement of high energy
leptons, photons and hadronic jets. Provide adequate performances for selected
high pt (> 1 GeV/c) probes for HI physics.
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0 1 2 10 100
pt (GeV/c)
Bulk propertiesHard processes
Modified by the medium
ALICE
CMS&ATLAS
3 Experiments
PID
T=QCD Qs
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QGP probes: hard processes modified by the medium
Q » QCD, T, Qs , r ~ 1/Q
Jet quenching: Energy degradation of leading hadrons, pt
dependence; Modification of genuine jet observables; Mass dependence of energy loss (light and heavy
quarks). Dissolution of c’onium & b’onium bound
states.
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Leading hadron quenching
Nuclear modification factor pattern very different at LHC: Final state interactions
(radiative & collisional energy loss) dominate over nuclear effects (shadowing+Cronin).
Measurement of suppression pattern of leading partons remains experimentally the most straightforward observable for jet-tomography analysis. 0 20 40 60 80 100
pt (GeV)
0.05
0.1
0.5
1
RAA
A+A √sNN = 200, 5500 GeV
Vitev&Gyulassy QM02
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Jets reconstruction Jets are produced copiously.
Jets are distinguishable from the HI underlying event.
pt (GeV)2 20 100 200
100/event 1/event 100K/year
100 GeV jet + HI event
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Performance by ATLAS
50 150 250 3500
40
80
%
Efficiency
Fake jets
Et
Cone algorithm R=0.4Et > 30 GeV
50 150 250 350Et
0
20
10
Energy resolutionPbPb
pp
E/E (%)
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50 150 250 3500
40
80
%
Et
0
20
10
E/E (%)
200 3000 1000
Performance by CMS
Cone algorithm R=0.5Et > 30 GeV
Energy resolution
Et
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Jet quenching Excellent jet reconstruction…
but challenging to measure medium modification of its shape…
Et=100 GeV (reduced average jet energy fraction inside R): Radiated energy ~20% R=0.3 E/E=3% Et
UE ~ 100 GeV
RMedium induced redistribution of jet energy occurs inside cone.
C.A. Salgado, U.A. Wiedemann hep-ph/0310079
vacuum
medium
Et = 50 GeV
Et = 100 GeV
0.200
0.4 0.6 0.8 1
0.2
R=√(2+2)
0.4
0.6
0.810
0.20.4
0.6
0.8
1
(R
)
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Exclusive jets: Redistribution of jet energy
Jet shape: distance R to leading particle; pT of particles for R < Rmax;