Trigger Support based on Discrete Cosine Transform for a Detection of Very Inclined Showers in Water Cherenkov Detectors

The paper presents results from a trigger based on the Discrete Cosine Transform (DCT) for simulated Extensive Air Showers developed in the atmosphere. The standard trigger for water Cherenkov detectors based on the 3-fold coincidence for a fixed threshold above the pedestal. The efficiency of the standard trigger decreases for very inclined showers. The DCT trigger operating in parallel with the standard one can improve the efficiency of detection of currently neglected events.We obtained the ADC patterns (digitized profiles of signals from photo-multipliers) using two simulation packages. The first package (CORSIKA) simulated a development of the extensive air showers (electromagnetic, hadron and muonic components) in the atmosphere till the level of the detectors. A set of coordinates and impetus is an input for the second simulation package OffLine which simulates a generation of Cherenkov light in water Cherenkov detectors and next the response of the PMTs as digitized signals after ADCs. We simulated avalanches of the particles for various energies, angles and slant depths for protons and muon neutrinos. These patterns were used for the online pattern recognition technique based on the Discrete Cosine Transform and implemented in the FPGA with the sampling frequency up to 120 MHz.The analyzes shows that for very inclined showers the trigger efficiency can increase at a level of 15-38%, if the standard trigger is supported by the DCT one.