Some DAMA/LXe results on 2β decay
2001  Preliminary new and improved limits on ^{136}Xe 2β
decay modes (running time 6843.8 h, ~6.5 kg LXe enriched in ^{136}Xe at 68.8%):
Note that the competitive limits for the processes with two ν
have cautiously been obtained without applying any background subtraction.
In particular, the limit on the halflife of the
2β2ν(0^{+} → 0^{+})
process in ^{136}Xe is in the range of the
theoretical estimate by A.Staudt et al., Europhys. Lett. 13 (1) (1990), 31;
moreover, theoretical estimates on halflife of 2β
decay processes suffer of the large uncertainties typically associated to the
calculations of the nuclear matrix elements.
The transition probability of the 2β2ν(0^{+} → 2^{+})
process is obviously depressed with respect to this latter one.

Decay Mode  T_{1/2} (y) (90% C.L.)


2β0ν(0^{+} → 0^{+})  > 7.0 x 10^{23}


2β0ν (0^{+} →
2^{+})  > 4.2 x 10^{23}


2β 0νM (0^{+} →
0^{+})  > 8.9 x 10^{22}


2β 2ν (0^{+} →
0^{+})  > 1.1 x 10^{22}


2β 2ν (0^{+} →
2^{+})  > 1.0 x 10^{22}



 < m_{ν}>
(eV)  < g_{M}> (10^{5})


Suhonen et al.  < 1.8  < 5.9


Engel et al.  < 2.2  < 7.1


Tomoda  < 1.5  < 4.8


Muto et al.  < 1.8  < 5.7



From the results obtained on the half life for the decay channels
2β0ν (0^{+} → 0^{+})
and 2β 0νM (0^{+} → 0^{+})
upper limits on the effective neutrino mass,
< m_{ν} >, and on the
effective coupling constant Majoronneutrino,
< g_{M} >, can be derived.
These limits depend on the evaluation of the nuclear matrix
elements, therefore they have been calculated (90% C.L.)
for various theoretical models.
