  The spinflip M1 resonance in the doubly magic nucleus $^{48}$Ca, dominated by
a single transition, serves as a reference case for the quenching of
spin-isospin modes in nuclei. The aim of the present work is a search for weak
M1 transitions in $^{48}$Ca with a high-resolution (p,p') experiment at 295 MeV
and forward angles including 0 degree and a comparison to results from a
similar study using backward-angle electron scattering at low momentum
transfers in order to estimate their contribution to the total B(M1) strength.
M1 cross sections of individual peaks in the spectra are deduced with a
multipole decomposition analysis. The corresponding reduced B(M1) transition
strengths are extracted following the approach outlined in J. Birkhan et al.,
Phys. Rev. C 93, 041302(R) (2016). In total, 29 peaks containing a M1
contribution are found in the excitation energy region 7 - 13 MeV. The
resulting B(M1) strength distribution compares well to the electron scattering
results considering different factors limiting the sensitivity in both
experiments and the enhanced importance of mechanisms breaking the
proportionality of nuclear cross sections and electromagnetic matrix elements
for weak transitions as studied here. The total strength of 1.19(6) $\mu_N^2$
deduced assuming a non-quenched isoscalar part of the (p,p') cross sections
agrees with the (e,e') result of 1.21(13) $\mu_N^2$. A binwise analysis above
10 MeV provides an upper limit of 1.62(23) $\mu_N^2$. The present results
confirm that weak transitions contribute about 25% to the total B(M1) strength
in $^{48}$Ca and the quenching factors of GT and spin-M1 strength are
comparable in fp-shell nuclei. Thus, the role of of meson exchange currents
seems to be neglible, in contrast to sd-shell nuclei.
