Study of low-energy antineutrino interactions on protons

We present a study of antineutrino interactions in hydrogen obtained in a 138000-picture run at the BNL 7-ft bubble chamber. The antineutrino beam had an energy distribution that peaked at {~}1.1 GeV. The cross section measured for charged-current interactions is ${σ}({{ν}}p{→}{{μ}}⁺+anything)=(0.32±{}0.08)×{}{10}^{{-}38}×{}[{E}_{{{ν}}} (GeV)]$ ${cm}²$. The neutral-current cross section is ${σ}({{ν}}p{→}{{ν}}p{{π}}⁺{{π}}^{{-}})={5.5}_{{-}2.6}+4.4×{}{10}^{{-}40}$ ${cm}²$. The ratio of strangeness-changing to non-strangeness-changing charged currents is ${R}ₛ={0.06}_{{-}0.05}+0.13$. An upper limit determined for charm production is ${{σ}}c<3.8×{}{10}^{{-}40}$ ${cm}²$ at the 90% confidence level. From the momentum-transfer distribution we measure average ${Q}²$ for inelastic charged-current events with energy greater than 2 GeV, $〈{Q}²〉=(0.10±{}0.03)[{E}_{{{ν}}} (GeV)]+(0.10±{}0.09)$ (${GeV/c)}²$. Using a maximum-likelihood method we determine from the quasielastic events ${{ν}}p{→}{{μ}}⁺n$ an axial-vector mass ${M}A={0.9}_{{-}0.3}+0.4$ ${GeV/c}²$.