Movement of Efimov states in 20C causing resonance in n-19C scattering near scattering threshold

Movement of Efimov states in 20C as a result of increasing the n-18C binding energy from about 100 to 500 keV is studied in a three body model for 20C, assumed to be n+n+18C system, employing separable potentials for the n-n and n-18C binary subsystems. The computational analysis shows that for small values of energies (< about 120 keV) which are just necessary to bind the two body (n-18C) system, there could be more than one bound Efimov states. But the states are found to go on disappearing one by one as the binding energy is increased beyond 200 keV. As originally pointed out by Amado and Noble [Phys. Rev. DPRVDAQ 5, 1992 (1972)], the Efimov states move into the unphysical sheet associated with the two body unitarity cut on increasing the strength of the binary interaction to bind the two body system. By undertaking a detailed study of the scattering of neutron on a bound (n-18C) system, we find that these states move over to the physical scattering region causing a resonance in n-19C scattering around neutron incident energy of 1.6 keV, having a width of about 0.25 keV