A highly unusual cosmic ray event at mountain altitude

Abstract

Search of rare massive particles in cosmic rays became an active field of research for several years. A recent theoretical study suggested the possible existence of strangelets in cosmic rays even at the mountain altitude. A common polymer, generally used as overhead projector transparencies, was identified as a solid state nuclear track detector (SSNTD) with a detection threshold Z/beta > 35. Those polymer detectors were exposed to cosmic rays at an altitude of 2.2 km as a trial experiment for setting up a large area array of detectors, aiming at the search of rare massive cosmic ray particles at mountain altitude. During the analysis of one such OHP detector we have found a highly unusual event. In the present paper we report our observation.