[en] 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 e⁺e^- pairs from the decay of the light vector mesons ρ,ω,phi and the low-mass continuum- in Au-Au collisions at √s_NN=200 GeV. From general considerations, the HBD has to identify electrons with a high efficiency (>90%) and with a double hit resolution better than 90%, it must have a pion rejection factor of at least 200 and a radiation budget of the order of 1% of a radiation length. The choice that emerges is a windowless Cherenkov detector, operated with a CF₄ based gas mixture in a special proximity focus configuration with a CsI cathode evaporated on GEMs