Fractionally charged particles in cosmic rays

TL;DR

This paper reviews experiments searching for fractionally charged particles in cosmic rays, discusses potential signals and detector methods, and presents new observations suggesting possible detection of such particles.

Contribution

It introduces new experimental evidence and simulation results supporting the existence of fractionally charged particles in cosmic rays and discusses detector techniques for their identification.

Findings

Change in proton energy spectrum at ~250 GeV possibly due to fractionally charged particles.

Detection of events with 4e/3 charge in the Aragats experiment.

Observation of a bump in the 2e/3 charge region with distinct angular distribution.

Abstract

The results of many experiments on a search of fractionally charged particles in cosmic rays have been reviewed. The registered by ATIC and PAMELA experiments change of the proton energy spectrum at about 250 GeV can be explained if fractionally charged particles with another energy spectrum slope actually mixed with protons but cannot be separated because of a strong dE/dx fluctuations. The performed simulations show that multilayer detectors can seriously help in such separation. In the Aragats experiment performed using multilayer proportional counter combined with hadron calorimeter a group of 4e/3 like events with unexpectedly high average energy has been registered. It could be explained by their different from regular hadrons energy spectrum. The ATIC experiment ionization spectrum in single charged particle area has been examined. An interesting bump in 2e/3 charge region was observed. The events in the bump have very different from regular protons angular distribution.