Status and Prospects of the CERNLHC Experiment ALICE

1
Status and Prospects of the CERN-LHC Experiment
ALICE

• Physics Issues
• Experimental Conditions
• Signals Observables
• The ALICE Experiment
• Layout
• Subdetectors

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The LHC

• 4 approved experiments Atlas, CMS, LHCb, ALICE
• 2006 start commissioning pp
• 2007 start PbPb
• vsNN 5.5 TeV ? Ecm (PbPb) 1148 TeV

0.2 mJ 1 g (0.5 m/s)2
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Cosmic Rays - The Knee
LHC reaches energies beyond the knee - at
drastically higher rates gt verification of
particle multiplicities from primary cosmic rays
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The Big Bang
1 km

quark-hadron transition
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Heavy-Ions at LHC Energies Probe Low-x Region
Hera

• x 2p0/vs
• pt p0 2 GeV
• (at mid-rapidity)
• Hera-Structure Fct
• gt large increase of initial gluon density at LHC

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High Energy Heavy-Ion Collisions are Dominated by
Hard Parton-Parton Collisions

• gluons/proton at p02 GeV SPS (4), RHIC (10),
  LHC (30)
• large cross section for gluon-gluon scattering
• partonic cascade with rapid equilibration at high
  temperatures (tlt 0.1 fm/c and T1 GeV)
• up to 5500 minijets (pt gt 2 GeV/c)

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Fireball Evolution of PbPb Collisions at the LHC

• high energy densities
• e? 1000 GeV/fm3
• et1 fm/c 40 GeV/fm3
• long life times
• tQGP gt10 fm/c
• tfreeze 70 fm/c
• large volumes
• dNch/dy 8000
• Vfreeze(Dy1) 105 fm3

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Comparison SPS-RHIC-LHC
PbPb, central collision (blt0.5 fm

• significant increase in relevant parameters (e,
  V, t)?
• factor 10 from SPS to LHC

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QGP probes
QGP phase
heavy meson decays
thermal radiation
jets
momentum distributions
collective flow
fluctuation, correlations
particle ratios
strangelets
HBT
light meson decays
hadron phase
phase transition
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Multiplicities for 208Pb208Pb collisions at LHC
PbPb at vs 5.5 ATeV

• 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
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Particle Ratios

• observables in ALICE
• ?, p, h, f, p, d, t, a K, L, X, W, D, B,
  J/Y???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

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Fluctuations Event-by-Event Physics

• low multiplicity events
• interesting excursions from normal physics
  masked by statistical fluctuations
• high multiplicity events
• LHC PbPb ideal to search for non-statistical,
  event-by-event fluctuations
• precision ? 1/vN
• EbE investigations can be extended to.
• pt spectra (p, K, p) ? temperature, flow
• HBT ? size, lifetime
• Ng/Nch ? isospin fluctuations (DCC)
• search for (critical) phenomena at phase
  boundaries (K/?, /-, )

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Passage of Hard Probes through Matter
resonance melting via color screening in hot
gluonic matter (J/Y suppression)
hard probes jets, J/??????..
dE/dx (energy loss) of parton significantly
enhanced for passage through hot gluonic matter
(jet quenching)
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Quarkonia Suppression Measurement

• two, complementary measurement of J/y and ?
  suppression in ALICE
• forward (?-arm 2.5 lt h lt 4)
• J/y , ??? ? m?m?
• ????er?????s (x 3)
• proven ???????? technology (NA38/50/60)
• mid-rapidity (ITSTPC TRD)
• J/ y , ??? ? ee-
• baryon-free region
• J/y ?? from B-decays can be tagged

gg ? cc ? J/?
? bb ? ?
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/y enhancement at
LHC (J. Stachel, P. Braun-Munzinger)
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Bottonium

• quality of data
• expected spectrum of the ?-family after 106 s (1
  ALICE year) running time as measured in the
  m-arm
• no suppression taken into account
• ?Dm 100 MeV aimed at (to resolve different
  states)

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Mid-Rapidity Open Charm/Bottom

• D-mesons (cq), B-mesons (bq)
• liftime ctD 0.032 cm, ctB0.039 cm
• semi-leptonic decays B, D ? e anything
• tagging via high pt electron (?TRD) displaced
  vertices (?ITS)

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Mid-Rapidity J/Y

• direct production gg ? cc ? J/?? ? ee-
• from B decay B ? J/?? ? ee-

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General 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

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Alice Setup
TOF
TRD
TPC
RICH
ITS
L3-Magnet
PMD
PHOS
µ-ARM
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ALICE _at_ Point2 Ready to move in!
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ALICE TPC Layout
5 m
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Pad Plane
570 000 pads (36 sectors)
pad size 4 ? 7.5 mm2
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TPC occupancy pad-time space
ALICE-simulation

• stability of chamber operation at high gain and
  load ? (v)
• occupancy (pad-time) _at_ inner chambers up to 50
  (!) ? cluster finding tracking very involved
• NA49 experience no track reconstruction at gt 20
  occupancy !

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Track Reconstruction at dNch/dy8300 BGND
outer radius 10 occupancy
STAR
inner radius 40-50 occupancy
ALICE Tracking-group improves since 1993
reconstruction algorithms (follow-your-nose-trac
king, Kalman-filter, ...)
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Track Reconstruction Momentum Resolution

• Status (2001)
• 88 of all (recognizable) tracks are recognized
  correctly (?)
• ??? fake tracks

• Momentum Resolution (TPC only )
• ltDpt/ptgt 2.4
• 5 GeV/c
• Dpt/pt 14 (?)
• for high pt physics complementary information
  necessary (ITS, TRD) ?
• ??Dpt/pt 5

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Transition Radiation Detector
TRD module

• 6 layers of TRDs 540 chambers, 1.16 ?106
  channels

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Transition Radiation Detector

• e/p discrimination employing transition radiation
  (ETR(g))
• p rejection factor gt 100

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Transition Radiation Detector - Trigger

• trigger capability - latency lt 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)

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Conclusion

• 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)

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TPC Production _at_ GSI HD
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TPC working principle - 3D-imaging