High-resolution (He3,t) measurements on the double β-decay (ββ) nucleus Ca48 have been performed at RCNP (Osaka, Japan) to determine Gamow-Teller (GT-) transitions to the nucleus Sc48, which represents the intermediate nucleus in the second-order perturbative description of the ββ decay. At a bombarding energy of E3He=420 MeV an excitation energy resolution of 40 keV was achieved. The measurements were performed at two angle positions of the Grand Raiden Spectrometer (GRS): 0° and 2.5°. The results of both settings were combined to achieve angular distributions, by which the character of single transitions could be determined. To characterize the different multipoles, theoretical angular distributions for states with Jπ=1+,2+,2-, and 3+ were calculated using the distorted-wave Born approximation (DWBA) Code DW81. The GT- strength was extracted up to Ex=7 MeV and combined with corresponding GT+ strength deduced from the Ti48(d,He2)Sc48 data to calculate the low-energy part of the ββ-decay matrix element for the Ca48 2νββ decay. We show that after applying trivial momentum corrections to the (He3,t) spectrum, the two reaction probes, (p,n) and (He3,t) reveal a spectral response to an impressively high degree of similarity in the region of low momentum transfer.
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