Proposal for a Hadron Blind Detector for PHENIX

A Hadron Blind Detector (HBD) is proposed as upgrade of the PHENIX detector at RHIC, BNL. The HBD will allow the measurement of low-mass ee pairs from the decay of the light vector mesons ρ, ω, φ and the low-mass continuum in Au-Au collisions at energies up to √ sNN= 200 GeV . From MC simulations and general considerations, the HBD has to identify electrons with very high efficiency (> 90%), double hit recognition better than 90%, moderate pion rejection factor of ∼ 200 and radiation budget of the order of 1% of a radiation length. The first choice under study is a windowless Cherenkov detector, operated with pure CF4, in a special proximity focus configuration with a CsI photocathode and a multistage GEM amplification element.