Neutrino-oscillation search with cosmic-ray neutrinos

It is shown that a sensitive search for neutrino oscillations involving more flavors than just nu/sub e/ and nu/sub μ/ is provided by measurement of the ratio of the total interaction rates of upward- and downward-going cosmic-ray neutrinos within a massive (approx. 10 kiloton) detector. Assuming mixing between all pairs of nu/sub e/, nu/sub μ/ and nu/sub tau/, the experiment is capable of observing time-averaging probabilities < P/sub e tau/>/sub t/ of magnitude set by mixing strengths corresponding to, e.g., the d- to s-quark mixing strength, and of reaching the limit δm/sub ij/2 identical with vertical bar m/sub i/2-m/sub j/2 vertical bar approx. = 10-4 eV2, where m/sub i/, m/sub j/ are neutrino mass eigenstates, and P/sub e tau/ and p/sub μ tau/ are the probabilities for nu/sub e/ and nu/sub μ/, respectively, to oscillate into nu/sub tau/ after traversing a distance L approx. = diameter of the earth