1. 1 PUTTING TWO AND TWO TOGETHER To accumulate things You can’t possibly use Is a burdensome Form of conceit. Or in other words: Never have two pairs of shoes If you haven’t got Two pairs of feet. Electron-Positron Pairs ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ Alberica Toia

2. 2 e + e  Pair Continuum at RHIC Possible modifications suppression (enhancement) Chiral symmetry restoration continuum enhancement modification of vector mesons thermal radiation charm modification exotic bound states Expected sources Light/Heavy hadron decays  cocktail –Dalitz decays    –Direct decays  and  –Direct decay J/  Hard processes –Charm (beauty) production Experimental challenge: COMBINATORIAL BACKGROUND 2 arm spectrometer acceptance: dN like /dm ≠ dN unlike /dm  different shape  event mixing like/unlike differences preserved in event mixing  Same normalization for like and unlike sign pairs Different independent normalizations used to estimate sys error –Measured like sign yield –Event counting –Geometrical Mean –Track counting All the normalizations agree within 0.5%

3. 3 The dielectron spectrum J/  continuum  Line shape analysis Hydro/coalescence J/  suppression recombination continuum Charm thermalization Thermal photons  spectral function  symmetry restoration 

4. 4 A Hadron Blind Detector (HBD) for PHENIX S/B ~ 100x Irreducible charm background signal electron Cherenkov blobs partner positron needed for rejection e+e+ e-e-  pair opening angle ~ 1 m Dalitz rejection via opening angle –Identify electrons in field free region –Veto signal electrons with partner HBD concept: –windowless CF4 Cherenkov detector –50 cm radiator length –CsI reflective photocathode –Triple GEM with pad readout Construction/installation 2005/2006 S/B increased by factor 100