Rambling Hadrons

There are mainly two ways to take into account non-zero neutrino masses…

1. Let’s modify the fields of the Standard Model (SM) by adding the right-handed neutrino. The main consequence is that in the SM lagrangian a mixing term for neutrino flavour pops up, parametrized by a matrix called the Pontecorvo-Maki-Nakagawa-Sakata matrix.
2. Let’s remove the renormalizability requirement from the SM: in the lagrangian we thus can have terms with dimension (in mass unit) of five or more. A consequence is that the SM can be valid only at energies lower than a certain energy scale Λ.

Fortunately, we have a way of deciding which one of the two is the more correct theory:

• the first solution breaks the individual lepton number conservation (flavour oscillations are allowed), but still conserves the total lepton number L.
• the second solution violates also the total lepton number.

Experiments were thus set to search for a violation of L in some physical process.

A process used for this purpose is the neutrinoless double-beta decay, (A,Z)→(A,Z+2)+2e^-, in which the variation of L is ΔL=2

At the Gran Sasso Laboratories, using 11 Kg of ⁷⁶Ge, some people searched many years for this decay.

Voices say something like: “the collaboration closed saying that no signal were found, but a few physicists (a so-called “Heidelberg-Moscow group”) published a bunch of articles claiming the evidence of a signal: however, there is criticism on their claim, concerning the correctness of their analysis, and on top of that their is the only such analysis existing, so it is not confirmed by anyone“. I read some of the main articles on the topic, and I have to say that the criticism seems to me to be well justified.

A couple links:

Evidence for Neutrinoless Double Beta Decay: the claim by the Heidelberg-Moscow people

Neutrino Oscillations and Signals in β and ∅νββ Experiments: review and criticism of the Heidelberg-Moscow results (yes, I admit, Ferruccio Feruglio is the professor here in Padova who taught me the details of the SM, but I assure you I’ve read the paper without any influence )

This entry was posted on Thursday, December 6th, 2007 at 2:35 am and is filed under Physics, Physics Today, Science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.