Study of broad-scale anisotropy of cosmic-ray arrival directions from 2 x 10(17) to 10(20) electron volts from fly's eye data

We report results on the broad-scale anisotropy of arrival directions of co smic rays in the energy range from 2 x 10(17) to 10(20) eV. The data were t aken by the Fly's Eye detector in both monocular and stereo modes of operat ion. We look for dependence on galactic latitude or supergalactic latitude by fitting the data to a Wdowczyk and Wolfendale plane enhancement function and a north-south gradient functional form. We report a small but statisti cally significant galactic plane enhancement in the energy range between 2 x 10(17) and 3.2 x 10(18) eV. The probability that this anisotropy is due t o fluctuations of an isotropic distribution is less than 0.06%. The most si gnificant galactic plane enhancement factor f(E) = 0.104 +/- 0.036 is in th e energy range (0.4-1.0) x 10(18) eV. No statistically significant evidence for a north-south gradient is found. There is no sign of significant devia tion from isotropic background when the data are analyzed in terms of super galactic latitude distributions.