Bonds for Detection of Very Inclined Showers Due to Anti-aliasing Filter in the Pierre Auger Surface Detector Data Acquisition System

Avalanches of secondary particles known as air showers consist from electromagnetic, hadron and muon components. For very inclined showers generated by hadrons, at the ground detection level only muon component survives forming thin muon pancake (~1m thickness). Ultra-relativistic charged particles crossing the water in a surface detector (SD) generate Cherenkov light detected by three PMTs. Direct hit of the Cherenkov light cone produces a signal pulse with a very short rise time and fast exponential attenuation.According to Nyquist theorem the spectrum of digitized signal should be cut-off above the frequency (f_c) equals a half of sampling frequency (f_S) by the anti-aliasing low-pass filter (AALPF). However, the AALPF suppresses the signal. Simulations and real measurements show that the amplitude may not be enough high for three-fold coincidences requiring be the T1 trigger.