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Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo 10.11.2004 Physics with ALICE Joakim Nystrand Institutt for Fysikk og Teknologi, Universitetet.

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Presentation on theme: "Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo 10.11.2004 Physics with ALICE Joakim Nystrand Institutt for Fysikk og Teknologi, Universitetet."— Presentation transcript:

1 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Physics with ALICE Joakim Nystrand Institutt for Fysikk og Teknologi, Universitetet i Bergen Evalueringsmøte Oslo November 2004

2 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo A Large Ion Collider Experiment = ALICE

3 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo How an event might look when 1000’s of particles are produced…

4 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Why collide heavy ions? Why not just increase the pp luminosity? Electromagnetic field  strong flux of photons.  and  A at unprecedented energies.

5 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Max. nucleon-nucleon center-of-mass energy (  s) vs. time Ions pp

6 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo or impact parameter. Two measures: Np : Number of participating nucleons N coll : 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

7 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Some results from RHIC  s = 200 GeV Comparison with pp – the R AA measure 

8 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Strong suppression of hadrons w/ p T >4 GeV/c seen by all RHIC exp. – ”jet-quenching”

9 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Jet-quenching and mono-jets pp: Two jets, back-to-back AA: Jet in only one direction in central collisions Azimuthal distribution of high p T particles What happens? Partons lose energy through gluon brems- strahlung as they traverse the medium. Bjorken (1982), Gyulassy & Wang (1992), …

10 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Jet-quenching is the most striking result from RHIC:

11 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Direct Photons ( =  not from hadronic decay) Hadrons: Strongly suppressed at high p T 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.

12 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo What happens in a heavy-ion collision? A state of matter with an energy density of at least  5-15 GeV/fm 3 is produced [ 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.

13 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Ultra-peripheral collisions Au+Au  Au+Au+e + e – M INV (e + e – )>1.5 GeV The e + e – pair can be produced through  e + e – or via J/  e + e – (  A  J/  A) Work in progress in PHENIX experiment at RHIC

14 Joakim Nystrand, Universitetet i Bergen Evalueringsmøte Oslo Conclusions for the future in ALICE: Goals: Focus on high p T - hadrons and photons Trigger on Ultra-Peripheral Collisions (b>2R A ). Example:  Pb  Pb Be open for new discoveries beyond the RHIC results. Means: PHOSHLTTPC


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