Cosmologists Provide Closest Measure of Elusive Neutrino


Cosmologists – and not particle physicists — could be the ones who finally measure the mass of the elusive neutrino particle. A group of cosmologists have made their most accurate measurement yet of the mass of these mysterious so-called “ghost particles.” They didn’t use a giant particle detector but used data from the largest survey ever of galaxies, the Sloan Digital Sky Survey. While previous experiments had shown that neutrinos have a mass, it is thought to be so small that it was very hard to measure. But looking at the Sloan data on galaxies, PhD student Shawn Thomas and his advisers at University College London put the mass of a neutrino at no greater than 0.28 electron volts, which is 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.

Their 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.

A neutrino is capable of passing through a light year –about six trillion miles — of lead without hitting a single atom.

Central to this new calculation is the existence of the largest ever 3D map of galaxies, called Mega Z, which covers over 700,000 galaxies recorded by the Sloan Digital Sky Survey and allows measurements over vast stretches of the known universe.

“Of all the hypothetical candidates for the mysterious Dark Matter, so far neutrinos provide the only example of dark matter that actually exists in nature,” said Ofer Lahav, Head of UCL’s Astrophysics Group. “It is remarkable that the distribution of galaxies on huge scales can tell us about the mass of the tiny neutrinos.”

The Cosmologists at UCL were able to estimate distances to galaxies using a new method that measures the colour of each of the galaxies. By combining this enormous galaxy map with information from the temperature fluctuations in the after-glow of the Big Bang, called the Cosmic Microwave Background radiation, they were able to put one of the smallest upper limits on the size of the neutrino particle to date.

“Although neutrinos make up less than 1% of all matter they form an important part of the cosmological model,” said Dr. Shaun Thomas. “It’s fascinating that the most elusive and tiny particles can have such an effect on the Universe.”

“This is one of the most effective techniques available for measuring the neutrino masses,” said Dr. Filipe Abadlla. “This puts great hopes to finally obtain a measurement of the mass of the neutrino in years to come.”

The authors are confident that a larger survey of the Universe, such as the one they are working on called the international Dark Energy Survey, will yield an even more accurate weight for the neutrino, potentially at an upper limit of just 0.1 electron volts.
The results are published in the journal Physical Review Letters.

Source: University College London

12 Replies to “Cosmologists Provide Closest Measure of Elusive Neutrino”

  1. “Cosmologists – and not particle physicists — could be the ones who finally measure the mass of the elusive neutrino particle. ”

    They can calculate until their blue in the face, but until that number can be verified through research, it’s just theory.

  2. Kevin, This is not just a theoretical abstraction. Known data was put together to get an upper bound on neutrino mass. The Super Kamiokande detector found the differences between the masses of different neutrino types.


  3. There was a recent paper about neutrino mass where a beam of Mu-neutrinos was sent from Batavia Ill. to a deep mine in Minnesota. This experiment measure the difference in mass of the various neutrino type, and has come up with some very interesting results. Anti-neutrinos have more of a mass difference Mu to electron than do neutrinos.

  4. Kevin, maybe you should read the provided source. The very reason for the press release was that it was one of the most accurate measurements to date, by way of an upper bound from data as LBC notes.

  5. Quantum theory bars the Universe from being deterministic right? So no amount of studying the state of sub-atomic particles will help you to extrapolate the state of the Universe and yet, amazingly, a large sky survey can help you set limits on the the properties of Neutrinos. Wow. I’m stunned, this must be how the palaeontologists felt when it took Geologists and Astronomers to work out what killed the Dinosaurs.

    Whoda thunkit?

  6. Quantum theory bars the Universe from being deterministic right?

    I think the claim is severely misdirected.

    Quantum mechanics (QM) is a theory on a deterministic process (takes states deterministically to states) with, in some theories, a stochastic coupling to the environment (entanglement with the environment, giving decoherence).

    We can readily observe the deterministic sector (classical effects). Due to the small decoherence time the pathways can diverge exponentially and we can have deterministic chaos, which severely limits our ability to make causally deterministic predictions.

    We can also observe the stochastic sector (quantum effects). Due to the large decoherence time phase effects makes pathways diverge quasi-linearly so no deterministic chaos, and the main contribution to difficulties to make causally deterministic predictions besides stochasticity is effects such as the “hockey rink” geometry on the wave unctions.

    In fact, in the many world theory of QM, the theory is fully deterministic over the many worlds, it is the correlations between universes that makes the observations within one universe stochastic.

    More to the point here, claiming that QM environmental effects on microstates (decoherence) bars the universe from having a classical deterministic sector is like claiming that thermodynamic environmental effects on microstates (entropy) bars the universe from having a classical time arrow.

  7. Neutrino oscillations are similar to the K-K-bar mechanism Feynman discusses in his Lectures on Physics Vol 3. The matrix is somewhat generalized, called the Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix. This has to do with the fact that the interaction Hamiltonian (a sort of energy operator) is not simultaneously diagonalizable with the fermion eigenstates.

    The NOVA detector is an underground neutrino detector in Minnesota. A neutrino beam of sorts, or where neutrinos are highly probable from a Tevatron experiment, is able to measure the transformation of a mu-neutrino into the other types. The difference in their masses determines these oscillations. If all the neutrino masses were equal the PMNS matrix would be diagonalizable with the fermion states and there would be no oscillations. So knowing how far they travel, and at nearly the speed of light one measure these oscillation periods.


  8. @ Torbjorn Larsson OM
    Thank you Torbjorn, your points are beautifully and succinctly argued as always.
    In Douglas Adams book The Restaurant at the End of the Universe, he describes how “The Total Perspective Vortex derives its picture of the whole Universe on the principle of extrapolated matter analyses.”
    “To explain – since every piece of matter in the Universe is in some way affected by every other piece of matter in the Universe, it is in theory possible to extrapolate the whole of creation – every sun, every planet, their orbits, their composition and their economic and social history from, say, one small piece of fairy cake.”
    What Douglas Adams, were he alive today, would write about this article, where the reverse process of analysing galaxies to determine upper limits on neutrinos mass, is a matter for humorous conjecture. My brief, flippant and misdirected attempt at paraphrasing was bound to bring forward a concise, detailed and considerate response such as yours, but I hope it hasn’t annoyed you.
    I’ll cut back on attempts at humor and try to stick quoting the Feyman lectures instead.

  9. For every electron/proton/neutron on earth there is a (very) small probability that it suddenly will quantum-leap itself to the moon.

    However, it is a very rare *sic* occurence that planets quantum-leap across the universe…

  10. Of course Richard Feynman was a not without humor as well…
    read “Surely You’re Joking Mr. Feynman!” and the hear audio tapes of his Physics Lectures.

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