Abstract
High multipole electromagnetic transitions are rare in nature. The highest-multipole transition observed in atomic nuclei is the electric hexacontatetrapole
E
6 transition from the
T
1
/
2
=
2.54
(
2
)
-min
J
π
=
19
/
2
-
isomer to the
7
/
2
-
ground state in
53
Fe with an angular momentum change of six units. In the present work, we performed ab initio calculations for this unique case by employing chiral effective field theory (EFT) forces. The in-medium similarity renormalization group is used to derive the valence-space effective Hamiltonian and multipolar transition operators. Bare nucleon charges were used in all the multipolar transition rate calculations, providing good agreement with the experimental data. The valence space takes the full
fp
shell. In
53
Fe, the low-lying states were dominated by the
0
f
7
/
2
component. Two different versions of the chiral EFT two- plus three-nucleon interaction were used to test the dependence on the interaction used. We also tested the convergence of the transition rate calculations against the harmonic oscillator parameter
ħ
Ω
and basis truncations
e
max
and
E
3max
for two- and three-nucleon forces, respectively.