Search for resonance decays to a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow></mml:math>plus jet in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mi>p</mml:mi></mml:math>scattering at DESY HERA

A study of the $\overline{\ensuremath{\nu}}$-jet mass spectrum in ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{p}\overline{\ensuremath{\nu}}X$ events at a center-of-mass energy 300 GeV has been performed with the ZEUS detector at the HERA collider at DESY using an integrated luminosity of 47.7 ${\mathrm{pb}}^{\ensuremath{-}1}.$ The mass spectrum is in good agreement with that expected from standard model processes over the $\overline{\ensuremath{\nu}}$-jet mass range studied. No significant excess attributable to the decay of a narrow resonance is observed. By using both ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{p}{e}^{+}X$ and ${e}^{+}\stackrel{\ensuremath{\rightarrow}}{p}\overline{\ensuremath{\nu}}X$ data, mass-dependent limits are set on the s-channel production of scalar and vector resonant states. Couplings to first-generation quarks are considered and limits are presented as a function of the ${e}^{+}q$ and $\overline{\ensuremath{\nu}}q$ branching ratios. These limits are used to constrain the production of leptoquarks and R-parity violating squarks.