We introduce a new technique to detect the discrete temperature steps that cosmic strings might have left in the cosmic microwave background (CMB) anisotropy map. The technique provides a validity test on the pattern search of cosmic strings that could serve as the groundwork for future pattern searches. The detecting power of the technique is only constrained by two unavoidable features of CMB data: (1) the finite pixelization of the sky map and (2) the Gaussian fluctuation from instrumental noise and primordial anisotropy. We set the upper limit on the cosmic string parameter as $Gmulesssim 3.7times 10^{-6}$ at the 95% confidence level (CL) and find that the amplitude of the temperature step has to be greater than $44mu K$ in order to be detected for the {it{Wilkinson Microwave Anisotropy Probe (WMAP)}} 3 year data.
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