Search for a new charged particle in the mass range of 2-100 MeV

Abstract: In the theory of electroweak interactions, there is no prohibition on the existence of particles with a mass other than that of an electron, muon and tauon. The task is to search for a new particle in the mass range of 2-100 MeV. The search was performed using the photo material of the 2-m propane bubble chamber. The chamber has been exposed in a 10 GeV proton beam at the JINR Synchrophasotron. For its search, ~55 thousand stereo photos have been scanned. The events of the $\gamma$ quantum conversion into a pair of charged particles have been analyzed. 50 anomalous events have been found in which one particle of the pair stops in the volume of the chamber, has an increased track density at the end of the range and, upon identification, detects a mass of ~ 8 MeV. The average value of the mass of the new particle is (8.5 $\pm$ 2.5) MeV