Synopsis: Neutrinoless Decays Are a No Show Again

A new experiment sets more stringent limits on neutrinoless double beta decay, thus further constraining the possibility that the neutrino and antineutrino are the same particle

The neutrino could be its own antiparticle, and this dual role could cause neutrinos to disappear from certain nuclear decays. Tentative evidence for neutrinoless decays appeared in 2004, in conflict with other experimental searches. A new experiment called Gerda has now conclusively refuted this positive result. The nondetection, reported in Physical Review Letters, places the most stringent limits yet on how frequently neutrinoless decays could occur.

Saying that neutrinos and antineutrinos have the same identity (as described by Ettore Majorana in 1932) conflicts with the standard model of particle physics, but it might explain why neutrinos have a much smaller mass than other particles. One way to test for the neutrino’s true nature is with double beta decay, in which two neutrons decay simultaneously into a pair of protons, electrons, and antineutrinos. In the Majorana picture, the same reaction could occur with an antineutrino emitted by one neutron being absorbed as a neutrino by a second neutron. In this neutrinoless double beta decay, the electrons would carry away all the emitted energy.

The Germanium Detector Array (or Gerda), located in the INFN Gran Sasso National Laboratory in Italy, reproduces the earlier 2004 experiment but with improved background suppression. The researchers indirectly detect neutrinos from the double beta decay of germanium-76 by measuring the energy spectrum of the emitted electrons. Neutrinoless decays would cause a peak in the number of events at the maximum electron energy. The Gerda collaboration (Agostini et al.) found no such peak in their data, which implies the rate of neutrinoless double beta decay—if it occurs at all—is less than 10-4 that of normal double beta decay. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

Particles and Fields

Previous Synopsis

Atomic and Molecular Physics

Photonic Matchmaking

Read More »

Next Synopsis

Fluid Dynamics

Riding Planetary Waves

Read More »

Related Articles

Viewpoint: A Doubly Charming Particle
Particles and Fields

Viewpoint: A Doubly Charming Particle

High-precision experiments at CERN find a new baryon containing two charm quarks. Read More »

Synopsis: A Precise Probe of the Quark-Gluon Plasma
Particles and Fields

Synopsis: A Precise Probe of the Quark-Gluon Plasma

Properties of the quark-gluon plasma can be inferred from measurements of jets and Z bosons simultaneously produced in the ion collisions that create the plasma. Read More »

Synopsis: Filling in a Tetraquark’s Profile
Particles and Fields

Synopsis: Filling in a Tetraquark’s Profile

An analysis of electron-positron collision data has determined the spin and parity of a particle thought to consist of four quarks. Read More »

More Articles