Measurement of the flux and zenith-angle distribution of upward throughgoing muons by Super-Kamiokande

A total of 614 upward throughgoing muonsof minimum energy 1.6thinspthinspGeV are observed by Super-Kamiokandeduring 537 detector live days. The measured muonflux is [1.74{plus_minus}0.07(stat){plus_minus} 0.02(sys)]{times}10{ sup{minus}13} cm{ sup{minus}2}thinsps{ sup{minus}1}thinspsr{ sup{minus}1} compared to an expected flux of [1.97{plus_minus}0.44(theor)]{times} 10{ sup{minus}13} cm{ sup{minus}2}thinsps{ sup{minus}1}thinspsr{ sup{minus}1} . The absolute measured flux is in agreement with the prediction within the errors. However, the zenith-angle dependence of the observed upward throughgoing muonflux does not agree with no-oscillation predictions. The observed distortion in shape is consistent with the {nu}{sub {mu}}{leftrightarrow}{nu}{sub {tau}} oscillation hypothesis with sin{ sup2}thinsp2{theta} {gt}0.4 and 1{times}10{ sup{minus}3}{lt}{Delta}m{ sup2}{lt}1{times}1 0{ sup{minus}1} eV{ sup2} at 90{percent} confidence level. {copyright} {ital 1999} {ital The American Physical Society}