Search for ββ decay in 136Xe: new results from the Gotthard experiment

Abstract The Gotthard Xe experiment has taken an additional 6013 hours of data with an upgraded readout system. Lower limits for the half-life of the double beta decay in 136 Xe are T 1/2 0 ν >4.4×10 23 yr (including 6830 hours taken in an earlier phase), T 1/2 0 νχ 0 >0.72×10 22 yr and T 1/2 2 ν >3.6×10 20 yr at 90% confidence level. Alpha spectroscopy, as well as βα and αα coincidence techniques lead to a determination of the activity of the gas of 10 −12 g/g effective of 232 Th and 238 U. Evaluations of background strongly suggest that an appreciable fraction of the ββ -candidates comes from the allowed 2 ν decay.