Sterile neutrinos do not exist

Apr 12, 2007 13:54 GMT  ·  By

The possible existence of "sterile neutrinos" has been a problem for the scientific community since the LSND experiment in the 1990s that appeared to contradict findings of other neutrino experiments worldwide by suggesting that some muon antineutrinos had flipped into electron antineutrinos after traveling about 30 meters.

The Liquid Scintillator Neutrino Detector (LSND) was a scintillation counter at Los Alamos National Laboratory that measured the number of neutrinos being produced by an accelerator neutrino source. The LSND project was created to look for evidence of neutrino oscillation, and its results conflict with the standard model expectation of only three neutrino flavors, when considered in the context of other solar and atmospheric neutrino oscillation experiments.

The particles come in three different types, or "flavors", dubbed electron, muon and tau. And several experiments have proved that neutrinos and their antiparticle counterparts can flip from one flavor to another, or "oscillate", as they travel.

Reconciling the LSND observations with the oscillation results of other neutrino experiments would have required the presence of a fourth, or "sterile" type of neutrino, with properties different from the three standard neutrinos. The existence of sterile neutrinos would throw serious doubt on the current structure of particle physics, known as the Standard Model of Particles and Forces. Because of the far-reaching consequences of this interpretation, the LSND findings cried out for independent verification.

So, physicists dismantled the experiment and used the parts to build a more sensitive experiment at Fermilab called MiniBooNE, the first phase of a project called BooNE (Booster Neutrino Experiment). Now, after analysing data from MiniBooNE gathered between 2002 and 2005, the team say they have resolved the issue, without the need for exotic sterile neutrinos.

MiniBooNE fired a beam of muon neutrinos into a detector 500 m away. None of them flipped into electron neutrinos. This result is consistent with other experiments and the standard three-neutrino picture.

Although the MiniBooNE researchers have decisively ruled out the interpretation of the LSND results as being due to oscillation between two types of neutrinos, the collaboration has more work ahead.