  Using analytical methods and Monte Carlo simulations, we analyze new
statistics designed to detect isolated step-like discontinuities which are
coherent over large areas of Cosmic Microwave Background (CMB) pixel maps. Such
coherent temperature discontinuities are predicted by the Kaiser-Stebbins
effect to form due to long cosmic strings present in our present horizon. The
background of the coherent step-like seed is assumed to be a scale invariant
Gaussian random field which could have been produced by a superposition of
seeds on smaller scales and/or by inflationary quantum fluctuations. We find
that the proposed statistics can detect the presense of a coherent
discontinuity at a sensitivity level almost an order of magnitude better
compared to more conventional statistics like the skewness or the kurtosis.
