E. Ma and M. Raidal
H. Georgi and S.L. Glashow;
R. Adhikari and G. Rajasekaran R. Adhikari, E. Ma and G. Rajasekaran"
J. Ellis and S. Lola
H. Minakata and O. Yasuda,
The article entitled
"Evidence for Neutrinoless Double Beta Decay" by
H.V. Klapdor-Kleingrothaus, A. Dietz, H.L. Harney and
I.V. Krivosheina (Vol. 16, No. 37) has been
In this article the authors have found
evidence for neutrinoless double beta decay for the first time.
This result is extremely exciting from several
grounds. The most important feature of this discovery is that it
establishes lepton number violation in nature for the first time.
The following is
the comment from Prof. E. Witten (Inst. Advanced Study, Princeton)
regarding the article:
If the result
mentioned in the article holds, it is a real landmark with the first
experimental confirmation of lepton number nonconservation, giving us an
important window on physics beyond the standard model, and the first
experiment beginning to give us results about the neutrino masses, as
opposed to mass differences.
something surprising about the result. Given the neutrino mass
differences as measured from the various solar and atmospheric neutrino
measurements, most theorists would have guessed that the effective
Majorana mass of the electron neutrino would be nonzero but smaller than
this experiment appears to suggest. Of course, most of us also expected
neutrino mixing angles to be small, and they have turned out to be
large! If this results holds, it points to a real surprise: either the
different neutrinos are surprisingly close to having the same mass, or
the mechanism of lepton number violation is more complicated than a
simple Majorana mass. Surprises like this are very good, but of course I
don't know at the moment which way this one would ultimately take us.
Since theoretical physicists guessed the roughly correct mass scale of neutrinos more than 20 years ago, in connection with Grand Unified Theories, and since lepton number violation was also suspected since this time, it is intriguing that these major successes of theory would be coupled with at least one big experimental surprise surprise (the large mixing angles) and maybe a second (if the value of the effective Majorana mass suggested by this experiment really holds).
Do the elementary
particles known as neutrinos have mass?
Yes, according to recent experiments. But how much?
A surprising - and controversial - result suggests that the answer is not what we thought.....
The experiments have also turned up a surprise: the measured 'mixing angles' (which determine the probability that neutrinos oscillate from one type to another) are much larger than theorists generally expected.
76Ge --> 76Se + 2e-. This reaction is called neutrinoless double-beta-decay, as the final state contains two electrons (historically known as beta-particles) and no antineutrinos - so the reaction violates the conservation of lepton number by two units. Taken together with the oscillation measurements, and assuming that the only relevant particles are the three known types of neutrino, the new result implies that the three neutrinos have approximately equal masses, probably a few tenths of an electron volt. This is a surprising result because other particle families, such as quarks and the charged leptons, do not have approximately equal masses (Fig. 1), and it will put a severe constraint on theories of the origin of neutrino masses.
....At any rate, planned future experiments using much larger quantities of 76Ge (or similar nuclei) will achieve much greater sensitivity. By extrapolating from the oscillation measurements, many physicists have guessed, prior to this claim, that a sensitivity 103 or 104 times greater than that of this experiment may be needed to conclusively observe the violation of lepton-number conservation. Such sensitivity suggests how difficult, as well as how potentially rewarding, future experiments are likely to be.
Neutrinoless double beta decay violates lepton number conservation, a fundamental tenet of particle physics. If confirmed, the consequences for particle physics will be profound.
Teilchen-/Atomphysik, 14.02.2002, Stefan Maier
Physik in unserer Zeit 33, No. 4, 155-155 (2002)
and \tau ---> \mu \gamma in terms of neutrino oscillation data, and show that these processes constrain the common neutrino mass scale and the solar neutrino oscillation solution in a very interesting range....
We found that neutrinos must be almost degenerate with the common mass scale of 0.2 eV or higher (!) in order to explain (g-2) and to satisfy \mu ---> e \gamma.
Phys. Rev. D 61(2000)097301 and hep-ph/9808293)
Phys. Rev. D 61(2000)031301 and hep-ph/9812361 )
Phys. Lett. B 486(2000)134 and hep-ph/0004197 )
Phys. Lett. B 458(1999)310 and hep-ph/9904279
Phys. Rev. D 56(1997)1692 and hep-ph/9609276