Speaker
Ms
Lotta Jokiniemi
(University of Jyväskylä)
Description
A reliable description of the double-beta-decay processes needs a possibility to test the
involved virtual transitions against experimental data. Unfortunately, only the virtual transitions
trough lowest $J^{\pi}$ states can be probed by the traditional electron capture or $\beta^-$-decay
experiments. The ordinary muon capture (OMC) offers a versatile tool to analyze the nuclear structure of the
intermediate states involved in double-beta-decay processes. In the present work the OMC rates for muon captures
on the nuclei $^{24}$Mg, $^{32}$S and $^{56}$Fe populating the low-lying states of the nuclei $^{24}$Na, $^{32}$P and
$^{56}$Mn are calculated.
The nuclear states for isobaric doublets $^{24}$Mg, $^{24}$Na, $^{32}$S, $^{32}$P and $^{56}$Fe, $^{56}$Mn are computed
by the nuclear shell-model code NuShellX@MSU. The $A=24$ and 32 states are computed in the $sd$-shell and $A=56$ states in
the $pf$-shell using different interactions without any configuration restrictions. The nuclear matrix elements and partial
capture rates to the lowest $J^{\pi}$ states of the daughter nuclei are computed using the one-body transition densities
(OBTDs) given by the shell-model code.
It has been found that the two lowest $1^+$ intermediate states play a significant role in the OMC processes. Also, the
lowest $2^+$ state has a strong impact on the transition rates. The OMC process can be used to probe the structure of the
intermediate states appearing in the double-beta-decay process since the associated momentum exchange is of the
order of 100 MeV, i.e. the same amount which is carried by the virtual Majorana neutrino in the neutrinoless
double beta decay. Experimental measurements in the near future can help
fine-tune the nuclear-structure parameters for the double-beta-decay calculations, but also give access to the
effective values of the axial-vector coupling $g_A$ and the induced pseudoscalar coupling $g_P$.
Primary author
Ms
Lotta Jokiniemi
(University of Jyväskylä)
Co-authors
Prof.
Dieter Frekers
(Westfälische Wilhelms-Universität, Münster, Germany)
Prof.
Hiroyasu Ejiri
(Research Center for Nuclear Physics, Osaka University)
Prof.
Jouni Suhonen
(University of Jyväskylä)
