We propose a new experiment sensitive to the detection of millicharged particles produced at the $30$ GeV proton fixed-target collisions at J-PARC. The potential site for the experiment is B2 of the Neutrino Monitor building, $280$ m away from the target. With $\textrm{ N}_\textrm{ POT}=10^{ 22}$, the experiment can provide sensitivity to particles with electric charge $3\times10^{ -4}\,e$ for mass less than $0.2$ $\textrm{ GeV}/\textrm{ c}^2$ and $1.5\times10^{ -3}\,e$ for mass less than $1.6$ $\textrm{ GeV}/\textrm{ c}^2$. This brings a substantial extension to the current constraints on the charge and the mass of such particles.
Categories: physics.ins-det hep-ex