joakim nystrand, universitetet i bergen evalueringsmøte oslo 10.11.2004 physics with alice joakim...
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Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Physics with ALICE
Joakim NystrandInstitutt for Fysikk og Teknologi,
Universitetet i Bergen
EvalueringsmøteOslo 10-11 November 2004
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
A Large Ion Collider Experiment = ALICE
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
How an event might look when 1000’s of particles are produced…
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Why collide heavy ions?
Why not just increase the pp luminosity?
Electromagnetic field strong flux of photons. and A at unprecedented energies.
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Max. nucleon-nucleon center-of-mass energy (s)vs. time
Ions
pp
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
or impact parameter.
Two measures:
Np : Number of participating nucleons
Ncoll : Number of binary (nucleon-nucleon) collisions
The collisions are characterized by their centrality
Use pp [or pA, or very peripheral AA] as base line.
No nuclear effects AA scales as Ncoll pp
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
dydpdN
dydpNdNpR
Tppinelppcoll
TAAEVTTAA //
/)/1()(
02
02
Some results from RHIC s = 200 GeV Comparison with pp – the RAA measure
ppColl
AA
Tppinelppcoll
TAAEVTTAA
NdydpdN
dydpNdNpR
//
/)/1()(
02
02
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Strong suppression of hadrons w/ pT>4 GeV/c seen by all RHIC exp.– ”jet-quenching”
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Jet-quenching and mono-jetspp : Two jets, back-to-backAA : 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), …
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Jet-quenching is the most striking result from RHIC:
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Direct Photons ( = not from hadronic decay)
Hadrons: Strongly suppressed at high pT
Direct photons: NOT suppressed.
QCD
Prediction if 0:s were not suppressed
Conclusion: The hadronic suppresion is a final-state effect caused by the medium when the partons/hadrons traverse it.
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
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.
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Ultra-peripheral collisions
Au+Au Au+Au+e+e– MINV(e+e–)>1.5 GeV
The e+e– pair can be produced through e+e– or via J/e+e– (AJ/A)
Work in progress in PHENIX experiment at RHIC
Joakim Nystrand, Universitetet i Bergen
Evalueringsmøte Oslo 10.11.2004
Conclusions for the future in ALICE:
Goals:• Focus on high pT - hadrons and photons• Trigger on Ultra-Peripheral Collisions (b>2RA). Example: PbPb • Be open for new discoveries beyond the
RHIC results.Means:
PHOS HLT TPC