Abstract: The SUB-Millicharge ExperimenT (SUBMET) is designed to search for particles with extremely small electric charges produced in proton fixed-target collisions at J-PARC. The detector, located 280 meters downstream of the target, consists of two layers of scintillator bars read out by photomultiplier tubes (PMTs). The dominant background arises from accidental coincidences between the two layers, primarily due to environmental radiation, PMT dark currents, and afterpulses. With an expected exposure of 5E21 protons on target, SUBMET will probe parameter space that has not been explored by previous experiments. Installed in spring 2024, the detector has collected beam data as well as auxiliary data for calibration. Using these datasets, single-photoelectron calibration and charge calibration with cosmic muons have been performed. In addition, background estimates based on beam-off data demonstrate the robustness of the prediction method and its applicability to beam-on conditions. In this talk, I will present the current status of the experiment and its future plans.
