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

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



A Large Ion Collider Experiment = ALICE



How an event might look when 1000’s of particles are produced…



Why collide heavy ions?

Why not just increase the pp luminosity?

Electromagnetic field strong flux of photons. and A at unprecedented energies.



Max. nucleon-nucleon center-of-mass energy (s)vs. time

Ions

pp



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



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



Strong suppression of hadrons w/ pT>4 GeV/c seen by all RHIC exp.– ”jet-quenching”



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), …



Jet-quenching is the most striking result from RHIC:



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.



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.



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



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

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

Documents

bergen evalueringsmte

rhic slide

alice slide

jetquenching slide

ncoll pp slide

time ions pp slide

e pair

r aa measure slide