June 22, 2010

Sterile Neutrinos are Back and Cosmological Progress to Determining Neutrino Mass

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1. Cosmologists at UCL are a step closer to determining the mass of the elusive neutrino particle, not by using a giant particle detector, but by gazing up into space. Neutrinos are one of the top candidates for dark matter.

Although it has been shown that a neutrino has a mass, it is vanishingly small and extremely hard to measure – a neutrino is capable of passing through a light year (about six trillion miles) of lead without hitting a single atom.



New results using the largest ever survey of galaxies in the universe puts total neutrino mass at no larger than 0.28 electron volts – less than a billionth of the mass of a single hydrogen atom. This is one of the most accurate measurements of the mass of a neutrino to date. The research is due to be published in an upcoming issue of the journal Physical Review Letters


The work is based on the principle that the huge abundance of neutrinos (there are trillions passing through you right now) has a large cumulative effect on the matter of the cosmos, which naturally forms into “clumps” of groups and clusters of galaxies. As neutrinos are extremely light they move across the universe at great speeds which has the effect of smoothing this natural “clumpiness” of matter. By analysing the distribution of galaxies across the universe (i.e. the extent of this “smoothing-out” of galaxies) scientists are able to work out the upper limits of neutrino mass. Although neutrinos make up less than 1% of all matter they form an important part of the cosmological model.


2. New Scientist - muon antineutrinos turn into electron antineutrinos at a higher rate than expected.

The excess could be because muon antineutrinos turn into sterile neutrinos before becoming electron antineutrinos

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