  We study an improved method for detecting gravitational wave (GW) signals
from perturbed black holes by earth-based detectors in the quest for searching
for intermediate-mass black holes (IMBHs). 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 multi-detector statistics primarily because of the
ineffectiveness of single-detector based discriminators of non-stationary
noise, such as the chi-square test, in the case of ringdown signals studied
here.
