A development of a Hadron Blind Detector for J-PARC E16 experiment

Spontaneous breaking of the chiral symmetry is considered to be the origin of hadron mass, however, the experimental confirmation is not given yet. J-PARC E16 experiment was proposed to investigate the origin of the mass through the mass modification of vector mesons in a finite density environment. The mass of the vector mesons are measured through electron-positron decay. A cherenkov detector with a high rate capability and fine segmentation is required for the electron identification. Hadron Blind Detector (HBD) is ideal for the purpose, which is a windowless cherenkov detector with a stack of GEMs on top of which CsI is evaporated. CF$_{4}$ works as amplification gas and cherenkov radiator in the HBD. We developed a prototype of HBD for J-PARC E16 experiment. It is constructed with a stack of an CsI-evaporated LCP-GEM with a thickness of 100$\mu$m and double kapton-GEMs with a thickness of 50$\mu$m. Very stable operation without severe damage from sparks is possible due to the lower voltage operation compared to triple 50$\mu$m kapton-GEMs. A beam test was performed with an electron beam at Tohoku Univ. The performance of the prototype will be reported and discussed.