Physics with ALICE

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Physics with ALICE
Joakim Nystrand Institutt for Fysikk og
Teknologi, Universitetet i Bergen
Evalueringsmøte Oslo 10-11 November 2004
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A Large Ion Collider Experiment ALICE
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How an event might look when 1000s of particles
are produced
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Why collide heavy ions?
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Max. nucleon-nucleon center-of-mass energy
(?s) vs. time
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The collisions are characterized by their
centrality
or impact parameter.
Two measures Np Number of participating
nucleons Ncoll Number of binary
(nucleon-nucleon) collisions
Use pp or pA, or very peripheral AA as base
line. No nuclear effects ? AA scales as Ncoll
? pp
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Some results from RHIC ?s 200 GeV Comparison
with pp the RAA measure
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Strong suppression of hadrons w/ pTgt4 GeV/c seen
by all RHIC exp. jet-quenching
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Jet-quenching and mono-jets
pp Two jets, back-to-back AA Jet in only one
direction in central collisions
Azimuthal distribution of high pT particles
What happens? Partons lose energy through gluon
brems- strahlung as they traverse the medium.
Bjorken (1982), Gyulassy Wang (1992),
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Jet-quenching is the most striking result from
RHIC
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Direct Photons ( ? not from hadronic decay)
Hadrons Strongly suppressed at high pT Direct
photons NOT suppressed.
Conclusion The hadronic suppresion is a
final-state effect caused by the medium when the
partons/hadrons traverse it.
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What happens in a heavy-ion collision?

• A state of matter with an energy density of at
  least
• ? 5-15 GeV/fm3 is produced 30-100 as dense as
  normal nuclear matter.
• The produced particles interact with the medium
  and lose energy as they traverse it.
• We can probe the medium with high-energy partons
  ? Jet-tomography.
• Strong collective effects are present - visible
  as radial and elliptic flow.

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Ultra-peripheral collisions
AuAu ? AuAuee MINV(ee)gt1.5 GeV
The ee pair can be produced through ???ee
or via J/??ee (?A?J/?A)
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Conclusions for the future in ALICE

• Goals
• Focus on high pT - hadrons and photons
• Trigger on Ultra-Peripheral Collisions
  (bgt2RA). Example ?Pb??Pb
• Be open for new discoveries beyond the RHIC
  results.