Speakers
Description
The investigation of mirror nuclei along the N = Z line is of considerable interest since it directly addresses the validity of the charge symmetry of nuclear forces and the role of Coulomb effects in determining nuclear structure. Isospin symmetry breaking effects are important to probe theoretical corrections to the superallowed Fermi decay matrix elements I = 0+, T = 1 → I = 0+, T = 1 between the isobaric analogue states, which are critical for precise determination of the leading element Vud of the Cabibbo-Kobayashi-Maskawa flavour-mixing matrix and, in turn, for further stringent tests of its unitarity, violation of which may signal new physics beyond the Standard Model of particle physics. In the limit of long wavelengths, where the Siegert theorem holds, the E1 transition operator is purely isovector. If the charge symmetry of the nuclear force is exact, E1 transitions between states of equal isospin are forbidden in N = Z nuclei and have equal strength in Tz=1/2 mirror nuclei. Experimental deviations from the two rules above can, therefore, be used to investigate isospin symmetry breaking. The aim of the present proposal is the measurement of the electromagnetic transition matrix elements for two E1 (forbidden) transitions in the N=Z=36 72Kr nucleus. This knowledge would allow us to probe the validity of the models used for the determination of the isospin mixing corrections in one of the heaviest nuclear system presently accessible. Excited states in 72Kr will be populated using the 40Ca+40Ca reaction, the LNL Tandem accelerator providing the 40Ca beam at an energy of 177 MeV. The proposed set-up will require AGATA coupled to the EUCLIDES Si-ball and the Plunger.
