Trans-Alps neutrinos

A beam of neutrinos manufactured at CERN shot through the Alps for the first time on 18 August. The beam will feed two neutrino oscillation experiments 730 km away at the Gran Sasso National Laboratory near Rome, Italy.

When it leaves CERN, the beam consists of muon neutrinos. Two detectors at Gran Sasso, the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) and Icarus, will look for the appearance of tau neutrinos as direct evidence of oscillation (see Physics Today, February 2000, page 50 ).

OPERA will also take advantage of a “small contamination of electron neutrinos” in the beam to search for θ₁₃, the last undetermined neutrino mixing angle, says Lucia Votano of Italy’s Frascati National Laboratory. The detector won’t be as sensitive to θ₁₃ as the reactor neutrino experiments (see the story on page 31).

In addition to providing a check of OPERA’s tau neutrino appearance results, Icarus will also look for sterile neutrinos—neutrinos that do not participate in the weak interactions (see Physics Today, January 2001, page 16 ). Such a discovery, says Icarus spokesman Carlo Rubbia of CERN, “will represent an immense step forward for the physics of neutrinos.”

OPERA is up and running, and Icarus is slated to start up in mid-2007.