The theory of nuclear displacement of levels of a proton-antiproton atom
Kudryavtsev A.E., Popov V.S.
A formula is obtained which expresses the displacement of the Coulomb levels of hadronic atoms in terms of the scattering length due to nuclear potential (without assumptions concerning the smallness of displacement). Experimental data on the shift of the Is -level of pp -atom indicate a possibility of the existence in the pp -system of a bound state with binding energy e S 0.9 MeV and width Γ 5 200 KeV.