We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the D0 experiment and correspond to an integrated luminosity of 94±5 pb−1. Assuming that R parity is violated via the single coupling λ′211, the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m0,m1/2) and (m˜χ,m˜ν) planes for λ′211=0.09, 0.08, and 0.07.Received 31 July 2002DOI:https://doi.org/10.1103/PhysRevLett.89.261801©2002 American Physical Society