1

PUTTING TWO AND TWO TOGETHERTo accumulate thingsYou can’t possibly useIs a burdensomeForm of conceit.Or in other words:Never have two pairs of shoesIf you haven’t gotTwo pairs of feet.

Elect

ron-P

ositro

n

Pairs

♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥

♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥

Alberica Toia

2

e+e Pair Continuum at RHIC

Possible modifications

suppression (enhancement)

Chiral symmetry restoration continuum enhancement modification of vector mesons

thermal radiationcharm modificationexotic 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:dNlike/dm ≠ dNunlike/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

The dielectron spectrumJ/

continuum

Line shape analysisHydro/coalescence

J/suppressionrecombination

continuumCharm thermalizationThermal photons spectral functionsymmetry restoration

4

A Hadron Blind Detector (HBD) for PHENIX

S/B ~ 100x

Irreducible charm background

signal electron

Cherenkov blobs

partner positronneeded for rejection 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