  Coherent one-particle one-hole (1p1h) excitations have given us effective
insights into general nuclear excitations. However, the two-particle two-hole
(2p2h) excitation beyond 1p1h is now recognized as critical for the proper
description of experimental data of various nuclear responses. The spin-flip
charge-exchange reactions $^{48}{\rm Ca}(p,n)^{48}{\rm Sc}$ are investigated to
clarify the role of the 2p2h effect on their cross sections. The Fermi
transition of $^{48}{\rm Ca}$ via the $(p,n)$ reaction is also investigated in
order to demonstrate our framework. The transition density is calculated
microscopically with the second Tamm-Dancoff approximation, and the
distorted-wave Born approximation is employed to describe the reaction process.
A phenomenological one-range Gaussian interaction is used to prepare the form
factor. For the Fermi transition, our approach describes the experimental
behavior of the cross section better than the Lane model, which is the
conventional method. For spin-flip excitations including the GT transition, the
2p2h effect decreases the magnitude of the cross section and does not change
the shape of the angular distribution. The $\Delta l=2$ transition of the
present reaction is found to play a negligible role. The 2p2h effect will not
change the angular-distributed cross section of spin-flip responses. This is
because the transition density of the Gamow-Teller response, the leading
contribution to the cross section, is not significantly varied by the 2p2h
effect.
