  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
