Commissioning of the electron identification system for Dilepton measurement in pA collisions at J-PARC

中須賀 さとみ; 江端 健悟; 市川 真也; 成木 恵; 佐甲 博之   ; 佐藤 進  ; 他26名*

Nakasuga, Satomi; Ebata, Kengo; Ichikawa, Masaya; Naruki, Megumi; Sako, Hiroyuki; Sato, Susumu; 26 of others*

Hadron mass spectra are expected to be modified in nuclear matter due to a partial restoration of chiral symmetry. We perform the J-PARC E16 experiment to measure the spectral modification of vector mesons in nuclei. We detect electron positron pairs from decays of mesons, produced in 30 GeV pA reactions. It is a key for our experiment to separate electrons from huge hadronic backgrounds. To identify electrons, we developed two-stage detectors comprising hadron blind detectors (HBDs) and lead-glass electromagnetic calorimeters (LGs). These detectors were constructed and installed at the J-PARC high-momentum beamline in 2020, and commissioning runs were performed in 2020 and 2021. The HBDs and the LGs were stably operated at a high counting rate generated in 10-MHz pA interaction at targets, and successfully detected electrons. In the preliminary results, the pion rejection powers were found to be 97.6 0.6% and 91.2 0.7% for the HBD and LG, respectively, which are consistent with the design performance, at the operation thresholds. Further evaluation of electron efficiency is ongoing.