Search for sub-millicharged particles at J-PARC

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Abstract
We studied the feasibility of an experiment searching for sub-millicharged particles (χs) using 30 GeV proton fixed-target collisions at J-PARC. The detector is composed of two layers of stacked scintillator bars and PMTs and is proposed to be installed 280 m from the target. The main background is a random coincidence between two layers due to dark counts in PMTs, which can be reduced to a negligible level using the timing of the proton beam. WithNPOT= 1022which corresponds to running the experiment for three years, the experiment provides sensitivity toχs with the charge down to 5×10−5inmχ<0.2 GeV/c2and 8×10−4inmχ<1.6 GeV/c2. This is the regime largely uncovered by previous experiments. We also explored a few detector designs to achieve optimal sensitivity toχs. The photoelectron yield is the main driver, but the sensitivity does not have a strong dependence on detector configuration in the sub-millicharge regime.

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