Mainz 2012 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 62: Nukleare Astrophysik
HK 62.2: Gruppenbericht
Freitag, 23. März 2012, 14:30–15:00, RW 2
High resolution (3He,t) reaction on the ββ decaying nucleus 136Xe — •Peter Puppe1, Dieter Frekers1, Annika Lennarz1, Jan Thies1, and Michael Holl2 — 1Inst. f. Kernphysik, 48149 Münster — 2Inst. f. Theor. Physik, 48149 Münster
A (3He,t) charge-exchange reaction experiment on the ββ decaying nucleus 136Xe has been performed at an incident energy of 420 MeV. The objective was to identify the Gamow-Teller (GT) strength distribution in 136Cs in an attempt to understand the long 2νββ decay half-life of 136Xe. The measurements have been carried out at the Grand Raiden spectrometer of the RCNP in Osaka, where an energy resolution of 42 keV was achieved. A new gas cell with thin windows made of polyethylene naphthalate has been employed as a target.
We find that the GT− strength distribution even at low excitation energies exhibits a rather normal behaviour compared to neighbouring nuclei like 128,130Te. A number of well isolated states up to about 4 MeV concentrated in two separate clusters have been resolved carrying a total B(GT−) strength of order unity. We argue that assuming exceptionally weak transitions from the GT+ side would be a rather improbable cause for the long half-life, whereas phase-cancelation effects for the 2νββ decay nuclear matrix elements seem to be a more natural and likely scenario. The data are confronted with the half-life measurement recently communicated by the EXO-Collaboration [1] and with recent theoretical calculations. The impact of phase cancellation on the neutrinoless decay will also be discussed.
[1] N. Ackerman et al., Phys. Rev. Lett. 107, 212501 (2011)