  Electron scattering in the monolayer graphene with short-range impurities
modelled by the annular well with a band-asymmetric potential has been
considered. Band-asymmetry of the potential resulted in the mass (gap)
perturbation in the Dirac equation. Exact explicit formulae for the scattering
matrix have been derived. The results are presented in terms of the scattering
phases and in the geometrical form of a relation between some 2-vectors. The
characteristic equation is obtained. It has a form of the orthogonality
condition. An approximate calculation of observables in terms the scattering
theory results is outlined.
