The CERN Neutrinos to Gran Sasso project (CNGS) has reached an important milestone with the successful first assembly of the target in a laboratory on the surface. Now the target is being dismantled prior to installation in its final location in the underground chamber.
On schedule for start-up in May 2006, CNGS will send a beam of neutrinos through the Earth to the Gran Sasso laboratory 730 km away in Italy, north-east of Rome, in a bid to unravel the mysteries of these elusive particles. To create the beam, a 400 GeV/c proton beam will be extracted from CERN’s Super Proton Synchrotron and directed towards the CNGS target, which consists of a series of graphite rods installed in a sealed container filled with helium. Positively charged pions and kaons produced by the proton interactions in the target will then be focused into a parallel beam by a system of two pulsed magnetic lenses – the horn and the reflector.
A 1 km-long evacuated decay pipe allows the pions and kaons to decay, in particular into muon-neutrinos and muons. The remaining hadrons (protons, pions and kaons) are absorbed in an iron beam dump with a graphite core. The muons will be monitored in two sets of detectors downstream of the dump, and then absorbed further downstream in the rock, while the neutrinos continue on towards Gran Sasso.
The target itself consists of 13 graphite rods, each 10 cm long and 4 or 5 mm in diameter. The first nine rods are interspaced by 9 cm of air, while the last four rods have no air-space between them; the 13 rods are together installed in a target unit. The CNGS target station contains five units – one active with four spares – in a rotatable target magazine. Together with a novel beam-position monitor (an electromagnetic coupler operated in air), the target magazine is installed on an alignment table. The four jacks to adjust the position of this table are fixed on a base table, and the entire assembly is installed inside an array of massive iron shielding blocks.
The neutrino beam will be completely installed by the end of 2005, and the first beam of neutrinos should head off next May.
