Image Processing Reference
In-Depth Information
The ability to analyze inclined showers with zenith angles larger than 60 induced by
neutrinos or photons essentially increases the acceptance of the surface array and opens a
part of the sky that was previously inaccessible to the detector. These showers provide a
new tool for ultra high energy cosmic rays interpretation because they are probing muons
of significantly higher energies than vertical showers. Spectral triggers offering a pattern
recognition in a frequency domain may improve a standard detection technique based on
the signal coincidences from many PMT channels above some thresholds in the time domain.
The "old" muon shower fronts have only a small longitudinal extension, which is leading
to short detector signals also in time. To identify these showers at the presence of "young"
showers with a large electromagnetic component one may need a very good spectral
sensitivity to the fast muon component in the trigger.
The main advantage of the spectral trigger is the scaling feature. The set of the DCT
coefficients depends only on the shape of signals, not on their amplitudes. Triggers sensitive
on the shape of FADC traces may detect events with expected characteristics i.e. the fast
attenuated, very short peaks related to the muonic, flat fronts coming from very inclined
showers. Independence of the amplitude is especially promising for the Auger North, where
due to a single PMT in the surface detectors the coincidence technique cannot be used. In
order to keep reasonable trigger rate for the 1st level trigger (ca. 100 Hz), the threshold for the
1st trigger should be much higher than for example in the Pierre Auger Observatory, where
3-fold coincidences attenuated a noise.
Fig. 1. Position of triggered surface detectors on the Auger array for the very inclined shower
(
= 83.5 ) nr 1155555. Muons triggered only few surface detectors, although they crossed
several hundred detectors. A distance between opposite detectors is 54 km.
θ
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