Challenges in Double Beta Decay

Table 13

K-ZEN	^136Xe (𝑄𝛽𝛽 = 2457 keV) stopped for upgrade
FWHM	240 keV
EXPOSURE	89.5 kg (^136Xe) × yr
MASS	179 kg (first data set) 125 kg (second data set) of ^136Xe
BKG
Rejection	Prompt and delayed coincidences + fiducial volume (FV)
Rate	∼1.5 × 10^−4 counts/(keV·kg·yr)
Sources	110𝑚Ag (probably due to Fukushima fallout, produces a peak near 𝛽𝛽(0𝜈))
𝑇^0𝜈1/2	>1.9 × 10^25 yr at 90% C.L.