By Dr David Whitehouse
BBC News Online science editor
French and Italian scientists are planning a large underground laboratory beneath the Alps designed to detect elusive particles from the Sun's core.
The new facility will be larger than Japan's Super-Kamiokande detector
It would consist of a huge tank filled with several hundred thousand cubic metres of ultra-pure water.
Detectors lining the tank would be sensitive to flashes of light caused by the passage of sub-atomic particles.
The lab would test theories in solar physics and help scientists understand the fundamental forces of nature.
It would be built adjacent to a road tunnel under the Frejus mountain near the French-Italian border.
The ambitious project has entered its earliest stages, with the main bodies that fund particle physics in France and Italy agreeing to start designing the facility.
The so-called Megaton Detector would be associated with another project under the Apennines, 120km east of Rome, called the Gran Sasso National Laboratory.
Scientists will look for flashes in the tank
The photomultiplier tubes that will line the huge tank of water would detect Cerenkov radiation given off by charged particles created in the tank by the passage of neutrinos.
Neutrinos are ghostly particles that do not interact very much with normal matter. Billions of them come streaming out of the Sun's core unhindered by the mass of the star.
In recent years it has been discovered that these neutrinos change subtly as they travel from the Sun to the Earth.
The thousand metres of rock would shield the detector from cosmic ray interference and allow more precise neutrino measurements than is currently possible.
The new laboratory would be larger and more precise than Japan's Super-Kamiokande detector.
The other aim of the new lab would be to observe the decay of particles called protons. If this could be detected it would provide valuable data that could help physicists reach a unified description of some of nature's fundamental forces.
If proton decay exists then the new detector should accumulate evidence for it in about five years.
Finding the money, designing the facility, excavating the cavern in the Alps and installing the equipment would take about 10 years, scientists estimate.
Physicists in the US and Japan also have plans for such a detector, but it is unlikely that more than one would be built.