rpp2010-rev-neutrinoless-double-beta-decay - – 1–...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: – 1– NEUTRINOLESS DOUBLE- β DECAY Revised August 2009 by P. Vogel (Caltech) and A. Piepke (University of Alabama). Neutrinoless double-beta (0 νββ ) decay would signal vio- lation of total lepton number conservation. The process can be mediated by an exchange of a light Majorana neutrino, or by an exchange of other particles. However, the existence of νββ-decay requires Majorana neutrino mass, no matter what the actual mechanism is. As long as only a limit on the lifetime is available, limits on the effective Majorana neutrino mass, on the lepton-number violating right-handed current or other possible mechanisms mediating 0 νββ-decay can be obtained, independently of the actual mechanism. These limits are listed in the next three tables, together with a claimed 0 νββ-decay signal reported by part of the Heidelberg-Moscow collaboration. A 6 σ excess of counts at the decay energy is used for a deter- mination of the Majorana neutrino mass. This signal has not yet been independently confirmed. In the following we assume that the exchange of light Majorana neutrinos ( m ν i ≤ 10 MeV) contributes dominantly to the decay rate. Besides a dependence on the phase space ( G ν ) and the nu- clear matrix element ( M ν ), the observable 0 νββ-decay rate is proportional to the square of the effective Majorana mass m ββ , ( T ν 1 / 2 ) − 1 = G ν · | M ν | 2 · m ββ 2 , with m ββ 2 = | ∑ i U 2 ei m ν i | 2 . The sum contains, in general, complex CP-phases in U 2 ei , i.e. , cancellations may occur. For three neutrino flavors, there are three physical phases for Majorana neutrinos and one for Dirac neutrinos. The two additional Majorana phase differences af- fect only processes to which lepton-number-changing amplitudes contribute. Given the general 3 × 3 mixing matrix for Majorana neutrinos, one can construct other analogous lepton number vi- olating quantities, m = ∑ i U i U i m ν i . However, these are currently much less constrained than m ββ . Nuclear structure calculations are needed to deduce m ββ from the decay rate. While G ν can be calculated reliably, the computation of M ν is subject to uncertainty. Indiscriminate averaging over all published matrix element values would result, for any given nuclide, in a factor of...
View Full Document

Page1 / 5

rpp2010-rev-neutrinoless-double-beta-decay - – 1–...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online