Synopsis: Still Waiting For Electron Decay

Scientists have placed new limits on how often electrons decay into neutrinos and photons, a reaction that—if it occurred—would violate the law of charge conservation.
Synopsis figure
Marco Pallavicini/INFN

Conservation of charge is thought to be a fundamental law of nature, so any experiment proving otherwise would upend the standard model of particle physics—and perhaps point physicists to new theories. Researchers have therefore studied the electron, the lightest of the known charged particles, to see if it might decay without conserving charge into two neutral particles (a neutrino and a photon). This possibility is, however, looking even more remote than previously thought. New results from scientists running the sensitive Borexino neutrino detector, buried deep in the Gran Sasso mountain in Italy, reveal that if such reactions occur, they happen less than once every 6.6×1028years.

Borexino consists of a shell of petroleum-based liquid that lights up when a neutrino, a nearly massless neutral particle, knocks an electron loose from one of the liquid’s atoms. The detector’s roughly 2000 photomultipliers then amplify and sense the emitted light. An international team of researchers calculated the sensitivity of the detector to photons produced via hypothetical electron decays into a photon and a neutrino. The detector, however, does not distinguish between photons produced in electron decay and neutrinos produced by the Sun or the radioactive decay of carbon, bismuth, and polonium in the surrounding rock. The authors therefore carefully modeled the background from these sources. They then looked for photon “events” above this background with energies near 256 kilo-electron-volts, an energy corresponding to half the electron rest mass. The researchers used 408 days’ worth of data to determine a mean electron lifetime roughly 2 orders of magnitude longer than the previous limit.

This research is published in Physical Review Letters.

–Katherine Kornei

Correction (11 December 2015): An earlier version of this Synopsis incorrectly stated that the researchers detected neutrinos. They detect photons.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Particles and Fields

Previous Synopsis

Particles and Fields

Black Hole Tests of Fermionic Dark Matter

Read More »

Next Synopsis

Related Articles

Viewpoint: Spinning Black Holes May Grow Hair
Gravitation

Viewpoint: Spinning Black Holes May Grow Hair

A spinning black hole may lose up to 9% of its mass by spontaneously growing “hair” in the form of excitations of a hypothetical particle field with a tiny mass. Read More »

Synopsis: Proton Loses Weight
Particles and Fields

Synopsis: Proton Loses Weight

The most precise measurement to date of the proton mass finds a value that is 3 standard deviations lower than previous estimates. Read More »

Viewpoint: Scattering Experiments Tease Out the Strong Force
Particles and Fields

Viewpoint: Scattering Experiments Tease Out the Strong Force

The scattering of protons from a carbon isotope can be used to test models of the strong force. Read More »

More Articles