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Neutrinos and 'the theory of everything'

distant detector

The distant detector will be a 5400-tonne sandwich of steel (to make the neutrinos interact) and scintillator (to reveal products of the interactions). Each steel sheet in the sandwich will be only 2.5 cm thick, but 8 m wide and 8 m tall.

To determine whether tiny neutrinos - thought to be the substance of the universe - have any mass at all, scientists plan to send thousands of them on a 730 km journey through rock 10 km below the North American Continent.

The project, called MINOS (Main Injector Neutrino Oscillation Search) will send neutrinos, produced at the Fermi National Accelerator Laboratory (Fermilab) in Illinois, USA to the Soudan Underground Laboratory in Minnesota, where they will be detected. The plan is to compare neutrinos detected close to the source at Fermilab with those observed in the distant Soudan Laboratory, to see if the neutrinos change. Neutrinos can change from one type to another only if they have some mass.

"The irrefutable determination that neutrinos are not massless would be the most exciting experimental measurement in the last twenty years and could prove to be the first major discovery of the next millenium' said Dr Jenny Thomas, who leads the MINOS team at University College London.

For many years physicists believed that neutrinos were mass-less as are photons (particles of light). However, recent experiments show that neutrinos might have very tiny masses.

Neutrinos weigh much less than particles such as electrons (the next lightest particle), but as neutrinos are so abundant they could provide a significant component of the total mass of the Universe. The theory that, up to now, has described all sub-atomic physics assumes that neutrino mass is zero. Proof that neutrinos have mass will give clues to the structure of the long sought underlying "theory of everything".

the Soudan Underground MineThe MINOS experiment will use Fermilab's newly-completed Main Injector particle accelerator to direct an intense beam of one type of neutrinos, called muon neutrinos, to a new 5000-tonne detector in the Soudan laboratory, some 700 metres underground. Beginning in early 2003, the MINOS physicists will use the detector to determine whether some of the muon neutrinos in the beam have changed to one of the other types of neutrinos, known as tau or electron neutrinos. Such a change from one type to another, would provide clear evidence for neutrino mass and would allow physicists to begin to calculate just how much mass the particles possess.

The MINOS experiment is a collaboration of some 200 scientists from China, Greece, Russia, the UK and the US.

Tags: physics