Monday, March 18, 2013

New Neutrinoless Double Beta Decay Limits

The Neutel 13 conference did not report any confirmed detections of neutrinoless double beta decay and updated the minimum half-life that is experimentally excluded based on results from the Kamland-Zen experment.
The half-life is measured to be larger than 1.9E25 years at 90%CL. If they combine this with EXO-200 results, the lower limit goes up to 3.4E25y. This corresponds to a 120-250 meV for the majorana neutrino mass. From this combined result one sees that there is inconsistency with the earlier claim of observing a signal in KK. . . . They . . . obtained lower limits on the zero-neutrino mode, which combined with EXO-200 gives an inconsistency with the KKDC claim at more than 97.5% confidence level.
This compares to a limited reported on this blog on June 5, 2012 limit of 1.6 * 10^25 years at EXO-200 (contradicting the KKDC claim at a 68% CI), and 2.6 *10^24 years at Kamland-Zen.

Efforts are underway to improve the precision of the observation at Kamland-Zen significantly (perhaps evne by a factor of 100) in the next few years.

The new combined limit it about twice that of the EXO-200 result of a year ago, and the exclusion of the claimed Heidleberg-Moscow neutrinoless double beta decay detection (called KK for lead investigator H. V. Klapdor-Kleingrothaus) now exceeds two sigma. The Heidlberg-Moscow experiment claimed finding at a six sigma level that would imply an effective Majorana mass of 0.2-0.6 eV (reference here) but rather than being replicated, it has been contradicted by two other experiments.

Neutrinoless double beta decay measurements are important within neutrino physics because they are necessary to determine in the neutrino has Majorana mass or only Dirac mass, and because they are predicted in a wide variety of beyond the Standard Model physics proposals including most supersymmetry (SUSY) theories.  See also here.

Generically, SUSY models with larger characteristic energy scales show greater levels of neutrinoless double beta decay.  And, the latest LHC results suggest that if SUSY does exist, it must have a high characteristic energy scale.  So, the combination of lower bounds on the SUSY energy scale from the LHC which are rising (to the mid-hundreds of GeV), and upper bounds on the SUSY energy scale from the neutrinoless double beta decay rate which are falling (to less than one TeV), put the squeeze on SUSY parameter space for all SUSY models except those that are fine tuned to suppress neutrinoless double beta decay.

Increasingly strict boundaries on the parameters of a Majorana mass other than the mass itself from experimental data are explored here.


andrew said...

A new study has pushed the limit to 3.0*10^25, about 50% longer than the limit in March.

andrew said...

Nemo-3 reports a limit based on total non-detection of 1.1*10^24 (90% CI).

This is corroborating of other results in a methodologically independent way, but is below state of the art in setting an exclusion confidence interval.

andrew said...

The Nemo-3 results add to the cumulative non-detection statistics from all non-Moscow experiments and the linked paper also discusses the SUSY bounds that it gives rise to, which is a function of squark and gluino masses.

andrew said...

More references on SUSY limits:

See, e.g., M. Hirsch et al., "Supersymmetry and Neutrinoless Double Beta Decay." (1995) and Allanach et al.,

Generically, a higher characteristic mass scale of a SUSY theory implies higher rates of SUSY mediated neutrinoless double beta decay (mostly via the R-parity violating parameter lamdaprime111). See, e.g., figures 9 and 10 in Vergados See also Gozdz

"n0νββ-decay provides a probe of the heavy SUSY mass scale and imposes constraints on RPV SUSY parameters" Prezeau