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- RHIC, PHENIXPHENIX Pad Chambers
- Net-Charge FluctuationsPredictionsPHENIX AnalysisComparison to simulations
OUTLINEOUTLINE
Relativistic Heavy Ion Collider (RHIC)Relativistic Heavy Ion Collider (RHIC)Au+Au Collisions 200 AGeV
Pad Chambers- Multi-Wire Proportional Chambers
- Fine Granularity Pixel Pad Readout
- Provide 3D Space Points for Track Recognition
Pad Chambers- Multi-Wire Proportional Chambers
- Fine Granularity Pixel Pad Readout
- Provide 3D Space Points for Track Recognition
- 172,800 Readout Channels
- Chip-On-Board Technique
Readout Cards (ROCS) Placed on the Chambers
- Data Transfer via Fiber Optic Links
Readout Card (ROC)
NET-CHARGE FLUCTUATIONS
Event-by-Event Fluctuationsof Net Electric Charge
in Local Regions of Phase Space
Decrease of Fluctuationsproposed as a signal for the QGP
Predictions range up to an 80% reduction
For each event:
Let n+ and n- denote the nr of positive and negative particles, respectively.
Net charge
Nr of charged particles
A very simple measure of net-charge fluctuations is then
since the variance of Q scales with nch .
But charge is a globally conserved quantityInstead of v(Q)=1, the hadron gas scenario yields:
where pa is the fraction of charged particles falling into the detector acceptance among all charged particles in the event.Also charge asymmetry, , has been taken into account.
where p+ and p- are the probabilities that aparticle is positive and negative, respectively.
A better measure of net-charge fluctuations is
which yields
in the hadron gas scenario.
NET CHARGE FLUCTUATIONS
RHIC 1st run period
GeVsNN 130
~ 500 000 events
|zvertex| < 17 cm
pT > 200 MeV/c
Reduction not as large as predicted for QGPConsistent with RQMD simulation
Global ChargeConservation
10% most central events
NET CHARGE FLUCTUATIONS
RHIC 2nd run period
GeVsNN 200
~ 850 000 events
|zvertex| < 17 cm
pT > 200 MeV/c
pT < 2 GeV/c
Hijingsimulations
r = 50
Using efficiency and charge asymmetry differences between track association cuts are removed
( 1 – pa )
Percentages show the fraction of particles generated withthe toy model. The rest is from pure global charge conservation.
Gaus(0.2,0.1)
Toy model of hadronization from QGP
- A very intriguing net-charge fluctuation centrality dependence is seen at 200 A GeV , not explainedby purely hadronic models.
- A comparison with a toy model of hadronization froma QGP shows that the initial predictions on a very drastic decrease of net-charge fluctuations may have been too optimistic.
- A large data sample at 200 A GeV is right now being prepared for analysis. Higher statistics and even more stable conditions during data taking will improve the measurements further.
SUMMARYSUMMARY