Observation of muon neutrino disappearance with the MINOS detectors and the NuMI neutrino beam

This letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current {nu}{sub {mu}} interactions are compared in two detectors located along the beam axis at distances of 1 km and 735 km. With 1.27 x 10{sup 20} 120GeV protons incident on the NuMI target, 215 events with energies below 30GeV are observed at the Far Detector, compared to an expectation of 336 {+-} 14.4 events. The data are consistent with {nu}{sub {mu}} disappearance via oscillations with |{Delta}m{sub 32}{sup 2}| = 2.74{sub -0.26}{sup +0.44} x 10{sup -3} eV{sup 2}/c{sup 4} and sin{sup 2} (2{theta}{sub 23}) > 0.87 (68% C.L.).