  A search for disappearance of active neutrinos over a baseline of 735 km was
conducted using the NuMI neutrino beam and the MINOS detectors. The data
analyzed correspond to an exposure of 3.18x10^{20} protons on target. The data
are fitted to neutrino oscillation models in which mixing with one sterile
neutrino is assumed. A comparison of the neutral-current-like spectrum at the
FD with the expectation derived from the near detector measurement shows that
the fraction of disappearing muon neutrinos converting to a sterile state is
less than 52% at the 90% confidence level. In addition, the possibility of
decay of active neutrinos into sterile species occurring concurrently with
neutrino oscillations was analyzed. Pure neutrino decay is disfavored at 5.4
sigma as an alternate explanation to oscillations for the depletion of muon
neutrinos at 735 km. The methodology employed in the analysis of neutral
current neutrino events observed in MINOS is described and newly obtained
results are presented.
