Pion-nucleon scattering in P{sub 11} channel and the Roper resonance

The {pi}N scattering in P{sub 11} channel is investigated within the two-channel model of Pearce and Afnan. The model consists of: (1) vertex interactions b {yields} {pi}N, {pi}{nabla} with b denoting either a bare nucleon or a bare Roper state, (2) a background potential {upsilon}{sub {pi}B,{pi}B} with B = N,{nabla}. Assuming that {upsilon}{sub {pi}B,{pi}B} can be phenomenologically parameterized as a separable form and the {pi}N inelasticity can be accounted for by dressing the {nabla} in the {pi}{nabla} channel by a {nabla} {leftrightarrow} {pi}N vertex, it is found that the fit to the P{sub 11} phase shifts up to 1 GeV favors a large mass of the bare Roper state. Our results are consistent with the findings of Pearce and Afnan that if the mass of the bare Roper state is restricted to be {le}1600 MeV, then a physical Roper will have a width which is too narrow causing a rapid variation of the phase shifts at energies near the resonance energy