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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
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♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥♥ ♥ ♥ ♥ ♥ ♥ ♥ ♥
Alberica Toia
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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%
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The dielectron spectrumJ/
continuum
Line shape analysisHydro/coalescence
J/suppressionrecombination
continuumCharm thermalizationThermal photons spectral functionsymmetry restoration
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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