First of a kind: The microscope display of the 'neutrino event' inside one of the bricks. The neutrino, coming from the left of the figure following an interaction, produces several particles identified by their tracks in the brick.

Credit: INFN (Italian National Institute of Nuclear Physics)

Related articles

• Launch of CERN particle accelerator delayed
• World's top particle accelerator malfunctions
• Dark matter and 'God particle' within reach
• LHC inches towards completion
• Particle wobble shakes up supersymmetry

PARIS: European physicists have sent a neutrino on a 730-kilometre trip under the Earth's crust and taken a snapshot of the instant it slammed into lab detectors.

Neutrinos are elementary particles that lack an electrical charge and do not appear to interact with mass, as they can travel through ordinary matter almost effortlessly. Trillions of them pass through our bodies every day. They come in three types, or 'flavours,' as physicists call them – electron, muon and tau.

Beaming neutrinos

The landmark journey from the European Organisation for Nuclear Research (CERN) in Switzerland to an underground laboratory at San Grasso, central Italy, took about 2.4 milliseconds, with the particle travelling close to the speed of light, France's National Centre for Scientific Research (CNRS) said yesterday.

In 2006, CERN started beaming neutrinos from its accelerator complex near Geneva, and have so far detected several hundred impacts in San Grasso. But the scientists have now taken the venture a step forward by starting to fill the San Grasso detector with small film plates which measure with high accuracy the cascade of particles that are produced when a neutrino impacts. These plates, called bricks, are each made of a sandwich of lead tiles and photographic films.

In the October 2 event, a neutrino hit one of the 60,000 bricks that had been installed in San Grasso, leaving a tell-tale track of a muon on the film. The experiment is important, say the investigators, as it could help explain one of the biggest mysteries about the Universe – its missing mass.

Missing mass

When scientists add up the mass of all the visible matter in the Universe, they arrive at a total of just 10 percent of what they know should exist. For years, neutrinos were not thought to have any mass, although that theory has been challenged by experiments at Japan's SuperKamioKande lab, which suggested that they may have a mass, albeit a very tiny one. The new experiment seeks to amplify and confirm this finding.

CERN sends San Grasso muon neutrinos, with the hope that a few tau neutrinos will show up at the other end among all the muons. If so, this would prove that neutrinos can oscillate between 'flavours' – and if so, the ability to switch can only be explained by mass. And if neutrinos do have mass, that could explain – at least in part – what happened to the universe's missing mass.

About 10 more "neutrino events" occurred in the following days, the CNRS press release said. Eventually, 150,000 bricks are to be installed in San Grasso.