Evidence for Neutral-Current Diffractive<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>π</mml:mi><mml:mn>0</mml:mn></mml:msup></mml:math>Production from Hydrogen in Neutrino Interactions on Hydrocarbon

Abstract

The MINERvA experiment observes an excess of events containing electromagnetic showers relative to the expectation from Monte Carlo simulations in neutral-current neutrino interactions with mean beam energy of 4.5 GeV on a hydrocarbon target. The excess is characterized and found to be consistent with neutral-current ${\ensuremath{\pi}}^{0}$ production with a broad energy distribution peaking at 7 GeV and a total cross section of $0.26\ifmmode\pm\else\textpm\fi{}0.02(\text{stat}.)\ifmmode\pm\else\textpm\fi{}0.08(\text{sys.})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}39}\text{ }\text{ }{\mathrm{cm}}^{2}$. The angular distribution, electromagnetic shower energy, and spatial distribution of the energy depositions of the excess are consistent with expectations from neutrino neutral-current diffractive ${\ensuremath{\pi}}^{0}$ production from hydrogen in the hydrocarbon target. These data comprise the first direct experimental observation and constraint for a reaction that poses an important background process in neutrino-oscillation experiments searching for ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ to ${\ensuremath{\nu}}_{e}$ oscillations.