Berlin 2005 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 38: Kernphysik/Spektroskopie

HK 38.6: Vortrag

Mittwoch, 9. März 2005, 15:30–15:45, TU MA004

Measurement of the nuclear matrix elements for 0νββ decay — •E.-W. Grewe, C. Bäumer, D. Frekers, S. Hollstein, and S. Rakers — Institut für Kernphysik, WWU Münster

The double beta decay is a rare second-order weak transition. A nucleus can undergo double beta decay with or without emission of neutrinos. The 0ν-mode is only possible if the neutrinos are massive Majorana particles or not purely left-handed. This mode is of great interest for neutrino-mass estimations, however the nuclear matrix element is needed to connect a measured half-life to the neutrino mass.

The nuclear matrix element can be calculated if the complete set of Gamow-Teller (GT) matrix elements for the two virutal transitions in the perturbative description are known. While for the 2ν mode only allowed GT transitions play a role, the 0ν mode rather proceeds through forbidden, i.e. higher multipole, transitions. An elegant way to experimentally obtain GT distributions are charge-exchange reactions. If transitions beyond the allowed GT ones have to be studied, high energy resolution spectra and angular distributions are necessary to precisely identify single excitations. We present new ⁴⁸Ca(³He,t) data taken at RCNP (Osaka, Japan) [1] which have energy resolutions of 40 keV so that the multipolarity of all low-lying states can be studied. Comparisons with theoretical calculations are presented. The data is combined with high-resolution ⁴⁸Ti(d,²He) data [2] to obtain 2νββ half-lives.

[1] H. Fujita et al., Nucl. Instr. Meth. A 484, 17 (2002).

[2] S. Rakers et al., Phys. Rev. C 70, 054302 (2004).