Negative-parity baryon masses using an O(a)-improved fermion action

We present a calculation of the mass of the lowest-lying negative-parity J=1/2{sup {minus}} state in quenched QCD. Results are obtained using a non-perturbatively {Omicron}(a)-improved clover fermion action, and a splitting found between the masses of the nucleon, and its parity partner. The calculation is performed on two lattice volumes, and at three lattice spacings, enabling a study of both finite-volume and finite lattice-spacing uncertainties. A comparison is made with results obtained using the unimproved Wilson fermion action.