The shooting

March 3, 2000

International scientists are attempting to shed light on the dynamics of the universe's mass. Paul Bompard reports from Rome

One of the most ambitious and costly experiments ever attempted in particle physics, the "shooting" of neutrinos from the Cern laboratories near Geneva, through 730km of the earth's crust, underneath the Alps, straight to the Gran Sasso laboratory, near Rome, is forging ahead after a recent decision by the Cern council. The project, involving an initial outlay, outside Cern's normal budget, of about Pounds 30 million, plus further spending of up to Pounds 90 million, was approved at a Cern council meeting in December.

Two-thirds of the initial cost will be covered by Italy's Istituto Nazionale di Fisica Nucleare (INFN), the rest by Belgium, France, Germany and Spain. Of the 20 countries that are full members of Cern, only three, including the United Kingdom, voted against the project, mainly because they are involved in similar or complementary research elsewhere, or felt that the money might be better spent otherwise. The UK, for instance, is committed to experiments at the Fermi Laboratory in Chicago.

"The project is of great importance because it should demonstrate that neutrinos have some mass and that they transform from one type of neutrino into another," said Claude Detraz, research director of Cern.

The experiments, which should begin providing data around 2005, hinge on an issue very dear to many physicists, that of the "nature" of neutrinos. The neutrino was first theorised in 1930 by Wolfgang Pauli and detected in 1955, and according to a "standard theory" has no mass. The Cern-Gran Sasso experiment is setting out to prove, instead, that they do have mass.

The Gran Sasso lab, a system of vast tunnels and enormous chambers carved out of solid rock and vividly reminiscent of the villain's high-tech hideout in a James Bond film, was built during the 1970s and 1980s, at enormous expense, 1.4km beneath the Gran Sasso mountain range.

Since almost all other forms of energy are unable to pass through 1.4km of rock - but neutrinos do - the idea was to have a "filtered" source of neutrinos to study. So far, results have been interesting but inconclusive.

The new Cern-Gran Sasso project hopes to go a step further.

Two types of neutrinos, neutron neutrinos and muon neutrinos, have been identified. But the existence of a third, the tau neutrino, is suspected. This is because in experiments to date some of the neutrinos seem to disappear.

The new experiments will try to prove the theory that these "disappearing" neutrinos are turning into tau neutrinos. If there is a transformation taking place, this should demonstrate that they have some mass.

"From our accelerator we will have a well-controlled, well-defined source of muon neutrinos, rather than a diffused source from the Sun," said Detraz. "By beaming a known quantity in a specific direction, we should be able to gauge more accurately what is arriving at the other end and what is happening along the way. If we find muons mixed with taus, this means some of the muons are oscillating and changing into taus, and thus have mass."

If it is discovered that neutrinos are "oscillating" and changing, this could help solve some of the mysteries regarding the dynamics of mass operating in the universe.

The FermiLab project is working on similar lines, a 730km underground "shoot" between Illinois and Minnesota, but the Cern-Gran Sasso experiments will focus specifically on the detection of the tau neutrinos into which the muon neutrinos are thought to be changing.

Most of the start-up money is being spent on constructing a 1km-long tunnel near Geneva, angled down 3 degrees to allow for the Earth's curvature, and aimed straight at the Gran Sasso laboratory under the Apennines east of Rome. The tunnel, which will be about 100m underground at the "muzzle" end, must be equipped with lifts and emergency exits, and it is along this tunnel that the "beam" of neutrinos will be generated.

Alessandro Bettini, director of the Gran Sasso lab, explained: "Two experiments are planned, 'Icanoe' and 'Opera'. These should cost between Pounds 33 million and Pounds 50 million each, to be paid for by the countries that are participating in each. 'Icanoe' is an Italian and Russian project, but we are open to other countries taking part. 'Opera' already has government financing from Japan, Italy is involved, and a number of other countries may also join in.

"We at Gran Sasso will prepare the space and adapt the laboratory as needed, but from then on the experiments will be based on broad international collaboration," said Bettini.

Italy's heavy involvement in the project reflects itsr long-standing love affair with physics, often marked by great success, which has always been a matter of national prestige. It also reflects the relative ease with which Italy's physicists have always obtained lavish funding from governments, often to the chagrin of researchers in other fields.

Detraz said: "It would be foolish at this point to talk about practical applications. These experiments are in the realm of very basic physics. What they may do is further our understanding of the universe, which may well have enormous applications in the long term.

"However, it would be very stupid to try to sell something that is purely cognitive as something that can be applied tomorrow. And any intelligent government knows this."

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