The ESS neutrino facility for CP violation discovery
Résumé
The relatively large value of the neutrino mixing angle $\theta_{13}$ measured in 2012 by neutrino reactor experiments opened the door to observe for the first time a possible CP violation in the leptonic sector. The measured value of $\theta_{13}$ also privileges the 2nd oscillation maximum for the discovery of CP violation instead of the usually used 1st oscillation maximum. The sensitivity at this 2nd oscillation maximum is about three times higher than for the 1st oscillation maximum inducing a lower sensitivity to systematic errors. Going to the 2nd oscillation maximum requires a very intense neutrino beam with the appropriate energy. The world’s most intense pulsed spallation neutron source, the European Spallation Source, has a proton linac with 5 MW power and 2 GeV energy. This linac also has the possibility to become the proton driver of the world’s most in- tense neutrino beam with very high potentiality to discover a neutrino CP violation. The physics performance of this neutrino Super Beam in conjunction with a megaton Water Cherenkov neu- trino detector installed 1000 m down in a mine at a distance of about 500 km from ESS has been evaluated. In addition, the choice of such voluminous detector will extent the physics program to proton–decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrades, the target station optimization and the physics potential are described. In addition to neutrinos, this facility will also produce at the same time a copious number of muons which could be used by a low energy nuSTORM facility, a future neutrino factory or a muon collider. The ESS neutron installations, under construction, will be fully operational by 2023 at which moment the upgrades for the neutrino facility could start. This project is now supported by the COST Action CA15139 “Combining forces for a novel European facility for neutrino-antineutrino symmetry-violation discovery” (EuroNuNet).