Status and Prospects of the CERN-LHC Experiment ALICE
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Epiphany - 3.1.-6.1.2002 H.R. Schmidt - GSI
Status and Prospects of the CERN-LHC Experiment ALICE
Status and Prospects of the CERN-LHC Experiment ALICE
• Physics Issues– Experimental Conditions
– Signals & Observables
• The ALICE Experiment– Layout
– Subdetectors
The LHCThe LHC
• 4 approved experiments: Atlas, CMS, LHCb, ALICE
• 2006: start commissioning pp• 2007: start Pb+Pb• √sNN = 5.5 TeV
Ecm (Pb+Pb) = 1148 TeV
≈ 0.2 mJ ≈ 1 g * (0.5 m/s)2
Cosmic Rays - The Knee
Cosmic Rays - The Knee
LHC reaches energies beyond the “knee” - at drastically higher rates =>
verification of particle multiplicities from primary cosmic rays
≈ 1 km
quark-hadron
transition}
Heavy-Ions at LHC Energies Probe Low-x Region
Heavy-Ions at LHC Energies Probe Low-x Region
x ~ 2p0/√s
pt ~ p0 ~ 2 GeV
(at mid-rapidity)
Hera-Structure Fct:
=> large increase of initial gluon density at LHC
Hera
High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton
Collisions
High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton
Collisions
• gluons/proton at p0=2 GeV: SPS (4), RHIC (10), LHC (30)
• large cross section for gluon-gluon scattering partonic cascade with rapid equilibration at high
temperatures (< 0.1 fm/c and T≈1 GeV) up to 5500 minijets (pt > 2 GeV/c)
Fireball Evolution of Pb+Pb Collisions at the LHC
Fireball Evolution of Pb+Pb Collisions at the LHC
high energy densities: ≈ 1000 GeV/fm3
=1 fm/c ≈ 40 GeV/fm3
long life times: QGP >10 fm/c
freeze ≈ 70 fm/c
large volumes: dNch/dy ≈ 8000
Vfreeze(y=1) =105 fm3
Comparison SPS-RHIC-LHCComparison SPS-RHIC-LHC
SPS RHIC LHC
Ecm [GeV] 17 200 5500
dch/dy 500 700 3000 - 8000
j [Gev/fm3]0=1fm/c ≈2.5 ≈3.5 15 - 40
Vfreeze [fm3] ≈103 ≈9103 ≈3.7104 - 1.0 105
QGP [fm/c] <1 ≈1 ≈4.5-12
Pb+Pb, central collision (b<0.5 fm
significant increase in relevant parameters ( V,factor 10 from SPS to LHC
QGP probesQGP probes
HBTHBT
momentumdistributions
momentumdistributions
particleratios
particleratios
light mesondecays
light mesondecays
strangeletsstrangelets
collective flowcollective flow
fluctuation,correlations
fluctuation,correlations
thermalradiation
thermalradiation
jetsjets
heavy mesondecays
heavy mesondecays
hadronphase
hadronphase
phasetransition
phasetransition
QGPphase
QGPphase
Multiplicities for 208Pb+208Pb collisions at LHC
Multiplicities for 208Pb+208Pb collisions at LHC
• predictions for dNch/dy vary from 3000 to 8000
• this reflects uncertainties in the (pQCD dominated) physics
– gluon shadowing
– initial/final state parton saturation
– jet-quenching
HIJING with jet-quenching
HIJING w/o jet-quenching
Pb+Pb at √s =5.5 ATeV
Particle RatiosParticle Ratios• observables in ALICE
, π, , p, d, t, K, , D, B, J/’s,
• particle composition thermodynamic parameters (Tfreeze, b) of hadronic phase
• strangeness content of fireball via strange/non-strange ratios QGP/phase transition– quality of strangeness measurement:
0
20
40K0
s1 event 10events
0.4 0.5 0.6ππ (Mass GeV)
1.1 1.2πp (Mass GeV)
10
30
Events/5MeV
0
100
1.3 1.4
- 103events
1.6 1.7 1.8
- 10 4events
25
50
75
π (Mass GeV) K (Mass GeV)
Fluctuations & Event-by-Event PhysicsFluctuations & Event-by-Event Physics
low multiplicity events:
• interesting excursions from “normal” physics masked by statistical fluctuations
high multiplicity events:
• LHC Pb+Pb ideal to search for non-statistical, event-by-event fluctuations– precision 1/√N– EbE investigations can be extended to:.
• pt spectra (π, K, p) temperature, flow• HBT size, lifetime• N/Nch isospin fluctuations (“DCC”)• search for (critical) phenomena at phase
boundaries (K/π, +/-, …)
speciesdN/dy
(ALICE)
π- ≈ π+ ≈ π0 2500
K+≈K-≈ K0s 385
500
p ≈ p 250
≈ 126
Passage of Hard Probes through Matter Passage of Hard Probes through Matter
hadronicmatter
QGPmatter
hard probes:jets, J/..
dE/dx (energy loss) of parton significantly enhanced for passage through hot gluonic matter (“jet quenching”)
resonance melting via color screening in hot gluonic matter (“J/ suppression”)
Quarkonia Suppression MeasurementQuarkonia Suppression Measurement• two, complementary measurement
of J/ and suppression in ALICE:
– forward (-arm: 2.5 < < 4)
– J/ , ’
• ers (x 3)
• proven technology (NA38/50/60)
– mid-rapidity (ITS+TPC +TRD)
– J/ , ’ e+e-
• baryon-free region
• J/ from B-decays can be tagged
1.0
0.5
light ions heavy ions
1 2 3 4 5 10 20 30 50 100
0.5
3(GeV/fm)
S,'
J /comovers
J /deconf.
Υ'comovers
Υ'deconf.
Υcomovers Υdeconf.
1.0
1) Sequential quarkonia suppression below Tc - in-medium modification of open charm/beauty thresholds (Digal, Petreczky, Satz)
2) Stat. hadronization of cc results in J/ enhancement at LHC (J. Stachel, P. Braun-Munzinger)
gg cc J/
bb
BottoniumBottonium
• quality of data:– expected spectrum of the -
family after 106 s (1 ALICE year) running time as measured in the -arm
– no suppression taken into account
– m ≈ 100 MeV aimed at (to resolve different states)
0
100
200
300
8 9 10 11 12m (GeV)
'
''
Mid-Rapidity Open Charm/Bottom Mid-Rapidity Open Charm/Bottom
• D-mesons (cq), B-mesons (bq)– liftime: cD= 0.032 cm, cB=0.039 cm
– semi-leptonic decays: B, D e + anything
– tagging via high pt electron (TRD) + displaced vertices (ITS)
Mid-Rapidity J/ Mid-Rapidity J/
• direct production: gg cc J/ e+e-
• from B decay: B J/ e+e-
General Design ConsiderationsGeneral Design Considerations
• only one dedicated HI-experiment at LHC:
• no single/dedicated probe/messenger of QGP correlated measurement of many observables versatile /general purpose experiment to study hot and dense matter
SPS
NA49 (hadrons)
CERES (di-electrons)
WA98 (photons)
NA57 (hyperons)
NA60 (muons)
RHIC
STAR (hadrons)
Phenix (photons, leptons)
Phobos (dN/d)
Brahms (p, π, K spectra)
LHC
ALICE (everything)
Alice SetupAlice SetupTPCTPC
TOFTOF
TRDTRD
ITSITS
PHOSPHOS
RICHRICH
µ-ARMµ-ARM
L3-MagnetL3-Magnet
PMDPMD
ALICE @ Point2: Ready to move in!ALICE @ Point2: Ready to move in!
ALICE TPC LayoutALICE TPC Layout
5 m
Pad PlanePad Plane
pad size: 47.5 mm2
≈ 570 000 pads (36 sectors)
TPC occupancy pad-time spaceTPC occupancy pad-time space
• stability of chamber operation at high gain and load ? (√)• occupancy (pad-time) @ inner chambers up to 50% (!)
cluster finding & tracking very involved– NA49 experience: no track reconstruction at > 20% occupancy !
ALICE-simulation
Track Reconstruction at dNch/dy=8300 + BGNDTrack Reconstruction at dNch/dy=8300 + BGND
outer radius: ≈ 10% occupancy
inner radius: 40-50% occupancy
ALICE Tracking-group improves since 1993 reconstruction algorithms(„follow-your-nose“-tracking, Kalman-filter, ...)
STAR
Track Reconstruction & Momentum Resolution
Track Reconstruction & Momentum Resolution
Status (2001):• 88% of all (recognizable) tracks
are recognized correctly ()• fake tracks
Momentum Resolution (TPC only ) :
•<pt/pt> ≈ 2.4%5 GeV/c:
• pt/pt ≈ 14% ()
for high pt physics complementary information necessary (ITS, TRD)
•pt/pt ≈ 5%
Transition Radiation DetectorTransition Radiation Detector
• 6 layers of TRD’s 540 chambers, 1.16 106 channels
TRD module
Transition Radiation DetectorTransition Radiation Detector
• e/π discrimination employing transition radiation (ETR())
• π rejection factor > 100
Transition Radiation Detector - TriggerTransition Radiation Detector - Trigger
• trigger capability - latency < 6 µs ( high pt electrons, jets) – very challenging real-time
front-end data processing
– select events which occur with probability 10-5
– enriches e.g. sample by factor 12 (194 ’s 2878 ’s per 106 s)
ConclusionConclusion
• heavy ions at LHC offer a large physics potential– goes beyond QGP search (pQCD)
– significant step beyond RHIC
• ALICE is a versatile detector– employing proven detector technology (TPC, µ-arm, silicon detectors))
– big advances in technology (TDR, front-end processing, TOF)
TPC Production @ GSI & HDTPC Production @ GSI & HD
TPC working principle - 3D-imagingTPC working principle - 3D-imaging
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