Measurement of quark momentum distributions in the proton using an antineutrino probe

Abstract

We present the results of a study of the inclusive reaction $\overline{\ensuremath{\nu}}p\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{X}^{0}$ for antineutrino energies from 5 to 150 GeV. The data were obtained by exposing the Fermi National Accelerator Laboratory hydrogen-filled 15-foot bubble chamber to a wide-band antineutrino beam. This is the first high-energy antineutrino experiment in which a pure proton target was used. The experimental problems of selecting the required sample of charged-current antineutrino-induced events are discussed in detail. A Monte Carlo simulation of the experiment is used to provide correction factors to the measured distributions. A measurement of the $x$ dependence of the inelasticity ($y$) distributions gives the proton structure functions ${F}_{2}^{\overline{\ensuremath{\nu}}p}(x)$ and $x{F}_{3}^{\overline{\ensuremath{\nu}}p}(x)$ up to an overall normalization constant. When expressed in terms of the quark-parton model, the quark distributions $u(x)$ and $\overline{d}(x)+\overline{s}(x)$ are determined. The results for $u(x)$ are found to be in excellent agreement with models based on fits to electron and muon scattering data. Using these results to fix the $u(x)$ normalization, an absolute measurement is made of $x[\overline{d}(x)+\overline{s}(x)]$, the antiquark momentum distribution.