A Search for $0^{+}$ States in ${}^{50}$Cr: Implications for the Superallowed $\beta$-decay of ${}^{50}$Mn

Abstract

A ${}^{52}$Cr$(p,t)$${}^{50}$Cr two-neutron pickup reaction was performed using the Q3D magnetic spectrograph at the Maier-Leibnitz-Laboratorium in Garching, Germany. Excited states in ${}^{50}$Cr were observed up to an excitation energy of 5.3 MeV. Despite significantly increased sensitivity and resolution over previous work, no evidence of the previously assigned first excited $0^{+}$ state was found. As a result, the $0_2^{+}$ state is reassigned at an excitation energy of $E_x=3895.0(5)$ keV in ${}^{50}$Cr. This reassignment directly impacts direct searches for a non-analogue Fermi ${\beta }^{+}$ decay branch in ${}^{50}$Mn. These results also show better systematic agreement with the theoretical predictions for the $0^{+}$ state spectrum in ${}^{50}$Cr using the same formalism as the isospin-symmetry-breaking correction calculations for superallowed nuclei. The experimental data are also compared to $ab$-$initio$ shell-model predictions using the IM-SRG formalism based on $NN$ and $3N$ forces from chiral-EFT in the $pf$-shell for the first time.

Comments: Accepted for Publication in Physical Review C as a Rapid Communication