Improved measurement of muon antineutrino disappearance in MINOS

We report an improved measurement of ?¯ µ disappearance over a distance of 735 km using the MINOS detectors and the Fermilab Main Injector neutrino beam in a ?¯ µ-enhanced configuration. From a total exposure of 2.95×1020 protons on target, of which 42% have not been previously analyzed, we make the most precise measurement of ?m¯ 2=[2.62-0.28+0.31(stat)±0.09(syst)]×10-3??eV2 and constrain the ?¯ µ mixing angle sin?2(2?¯ )>0.75 (90% C.L.). These values are in agreement with ?m2 and sin?2(2?) measured for ?µ, removing the tension reported in [ P. Adamson et al. Phys. Rev. Lett. 107 021801 (2011)].