A new experimental limit for the stability of the electron

A lower limit of >1.22×1026 yr (68% c.l.) has been determined for the mean life time of electron decay via the branch e−→γ+νe. The limit was deduced from the spectra measured in the period 1995-2003 with the full set-up of 5 enriched 76Ge detectors of the Heidelberg-Moscow ββ experiment in the Gran Sasso underground laboratory. One of the detectors, and the setup 1 consisting of four detectors show an indication of a signal on a 1.4σ C.L. The best limit given by a single detector is 1.93×1026 yr. The result is the by far sharpest limit obtained with Ge detectors. When comparing it with other limits, e.g. that from Borexino [H.O. Back, et al., Phys. Lett. B 525 (2002) 29] it may be essential to note that the present limit has been deduced from the raw data without any treatment of the background, and also, that the energy resolution in the present experiment is much larger than in the other most sensitive experiments. Combined with the best laboratory limit on the photon mass the present result gives the following restriction for charge nonconservation: ϵeνγ<0.86×10−98 (68% c.l.) or <1.14×10−97 (90% c.l.).