Improved coincident and coherent detection statistics for searches for gravitational wave ringdown signals

We study an improved method for detecting gravitational wave signals from perturbed black holes by Earth-based detectors in the search for intermediate-mass black holes. Such signals, called ringdowns, are damped sinusoids whose frequency and damping constant can be used to measure a black hole's mass and spin. Utilizing the output from a matched-filter analysis pipeline, we present an improved statistic for the detection of a ringdown signal that is found to be coincident in multiple detectors. The statistic addresses the non-Gaussianity of the data without the use of an additional signal-based waveform consistency test. We also develop coherent network statistics to check for consistency of signal amplitudes and phases in the different detectors with their different orientations and signal arrival times. We find that the detection efficiency can be improved at least by a few tens of percent by applying these multidetector statistics primarily because of the ineffectiveness of single detector--based discriminators of nonstationary noise, such as the chi-square test, in the case of ringdown signals studied here.