Particles for export

3 November 1998

With CERN’s site straddling the Franco­Swiss frontier near Geneva, exporting particle beams is an everyday occurrence. Now a new proposal foresees CERN particles also being exported to Italy, for use in the Gran Sasso underground laboratory, 730 kilometres away.


This summer’s neutrino news underlined how little we really know about neutrinos. New data, notably from the SuperKamiokande detector, 1000 metres underground in a Japanese mine, show that the behaviour of neutrinos, the most inactive of known particles, is probably much more complex than originally supposed and poses many new physics questions.

Neutrinos come in three varieties ­ electron, muon, or tau according to which kind of weakly interacting particle (lepton) they escort. The new results suggest that this lepton allegiance can be temporary, changing as the neutrinos fly through matter. Neutrinos could be Nature’s floating voters ­ a neutrino which sets out preferring the company of muons could arrive favouring taus instead.

Some of the neutrinos picked up by SuperKamiokande and other underground detectors derive from cosmic rays crashing into the Earth’s atmosphere. These collisions produce unstable particles such as pions and kaons, which subsequently decay, and whose decay products can in turn decay, producing neutrinos. At face value, there should be twice as many muon-type neutrinos as electron-type. However, for some time, such underground detectors have been seeing fewer muonic neutrinos than expected.

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