Ghost Particle (almost) Measured

BBC is reporting that a presentation at the Weizmann conference, The Cosmic Enigma: Scientific Symposia, running at UCL on 22 and 23 June, will reveal that scientists have narrowed down the weight of one of the smallest particles, the neutrino, popularly known as the 'ghost particle.'  This discovery in the world of the very small depends upon examination of the world of the very large.  Scientists examined data on the distribution of galaxies in order to determine that mass of a neutrino is "no greater than 0.28 electron volts [which] ... is less than a billionth of the mass of a single hydrogen atom."  This is important because neutrinos are considered to be a verifiable component of Dark Matter.

The UCL report on the discovery is here.  On this site, the head of UCL's Astrophysics Group, Professor Ofer Lahav explained how the discovery was verified and how it relates to Dark Matter:

“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. It is remarkable that the distribution of galaxies on huge scales can tell us about the mass of the tiny neutrinos.” 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."

The results of the research will be published in Physical Review Letters.  For those of us who know nothing about neutrinos, it's still good to know that they come in three types, or flavours: muon, tau and electron. 

The MINOS Far Detector (left), mural by Joseph Giannetti (right).

In addition, scientists recently found neutrinos can switch from one flavour to another.  European efforts to isolate neutrino flavour changes are concentrated at the Oscillation Project with Emulsion-tRacking Apparatus, or OPERA project.  The MINOS experiment at Fermilab near Chicago, which is partly funded by the U.S. Department of Energy, was also established to measure neutrino type shifts.

 NuMI Horn 1. Reidar Hahn, Fermilab.

According to this report at the University of Minnesota, the NuMI Horn "generates a magnetic field to increase the intensity of the neutrino beam that will zip underground from the Fermi National Accelerator Laboratory outside Chicago to the new NOvA lab at Ash River."  The NuMI Off-Axis Electron Neutrino Appearance (NOvA) Detector Facility at Ash River is currently being built.  Construction began in June 2009.  As of April 2010, blasting was complete at the site. NOvA's research goals are described here and here.

The University of Minnesota report continues: "A high level of international interest in studying neutrinos has continued to develop in recent years. Neutrinos comprise three of the 12 fundamental building blocks of matter. They exist in large numbers in the Universe, due to production during the Big Bang and ongoing production in stars and by the cosmic rays that are naturally incident on the Earth from outer space."  For a list of the 12 elementary particles, go here.