High Energy Dilepton Experiments rhic rhic = Relativistic Heavy Ion Collider

High Energy Dilepton Experiments

RHIC

• RHIC = Relativistic Heavy Ion Collider

• located at Brookhaven National Laboratory

RHIC and its experiments

PHENIX in practice

PHENIX in principle

• 3 detectors for global event characterization

Au-Au collision as seen in PHENIX

PHENIX: tracking & particle ID

PHENIX measures dielectrons

• first attempt from 2002 Au-Au Run

• S/B ~ 1/500 (!) for minimum bias events
• not enough statistics

• Au-Au data taken in 2004

• ~ 100x statistics
• photon conversions reduced by factor 2-3
• expect background reduction by ~ 2

Low-mass e+e- pairs: the problem

Background shape: like sign

Background normalization: 2√N++N- -

Conversion rejection

Subtraction of “cross” pairs

Raw unlike-sign mass spectrum

Cocktail comparison

Comparison with theory

Reference: dielectrons in p-p

Comparison: p-p vs. Au-Au

Yield in different mass ranges

Centrality dependence

Summary

(Near) future precision e+e- measurement

• identification of dielectrons with small opening angle BEFORE one of the “legs” is lost

• electron ID before the magnetic field
• “full” acceptance electron detector

• new field configuration

•  HadronBlindDetector (HBD)

Hadron Blind Detector (HBD)

• Dalitz rejection via opening angle

• identify e± in field free region
• veto signal e± with partner

• HBD concept

• windowless CF4 Cherenkov detector
• 50 cm radiator length
• CsI reflective photocathode
• triple GEM with pad readout

• construction/installation 2005/2006 (repair 2007)

Future

Projections for RHIC: high energy

Projections for RHIC: low energy