Faint signatures in IceCube

Free fractionally charged particles are predicted in several extensions of the Standard Model of particle physics. They could have been produced in the early universe, in violent astrophysical processes or as a result of cosmic ray interactions in the upper atmosphere. Multiple experiments have searched for such particles with no evidence thus far. The IceCube Neutrino Observatory is a Cherenkov detector instrumenting a cubic kilometer of deep antarctic ice, suitable to search for particles carrying a fraction of the elementary charge. A previous IceCube analysis has shown a reduced trigger efficiency for particles with a charge of e/3 compared to higher analyzed charges. Due to the quadratic dependence of photon production processes on the charge, significantly less photons are emitted with a decreasing charge, resulting in faint tracks as a characteristic signature for these particles. The Faint Particle Trigger was developed to enhance the detection efficiency for faint signatures. It incorporates single isolated hits in the trigger decision, which are not used by the standard triggers that work on correlated hit pairs. The FPT was successfully deployed at South Pole and improves significantly the trigger efficiency for a broad range of charges, while increasing the event rate by a factor 1.004. This includes a relative improvement by a factor of 1.55 for a charge of e/3, compared to the standard triggers. The consecutively developed Faint Particle Filter further reduces the trigger rate of 100 Hz to approximately 8 Hz while keeping 85% of the triggered events for a charge of e/3. Implications by the Faint Particle Trigger and Filter are discussed.