Background reduction using single-photoelectron counting for WIMP search

We have developed a new background reduction method based on single photoelectron counting of scintillators for the WIMP search experiment. We introduced this method to our detector system ELEGANT VI, which has an active shield in all directions (4π) using a pulse height or, equivalently, the difference in the number of photoelectrons between two (left and right) photomultiplier tubes attached to CaF2 scintillators. The number distribution is uniquely described by a binomial function, via which we developed the unambiguous background subtraction method. This method reduces the backgrounds further compared to charge-sensitive ADC and offers improved sensitivity for the search for WIMPs.