Abstract:
The discovery of neutrino oscillations by SuperKamiokande and SNO proved, contrarily to what is assumed by the Standard Model, that neutrinos had a non-zero mass. After measuring in 2012 a relatively large value of the neutrino mixing angle θ13, the door is now open to observe for the first time a possible CP violation in the leptonic sector, one of the main unanswered questions in particle physics. The relatively high value of θ13 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 influence of systematic errors. Going to the 2nd oscillation maximum necessitates a very intense neutrino beam with the appropriate energy.

After some introduction in neutrino physics and experiments, it will be explained how to use the world’s most intense pulsed spallation neutron source, the European Spallation Source under construction at Lund (Sweden), to produce, on top of neutrons, a very high intensity neutrino beam. This neutrino beam can be used to tend to discover a neutrino CP violation by operating the facility at the 2nd oscillation maximum. A positive observation could explain under some assumptions the matter-antimatter asymmetry in the Universe.

The physics performance of that neutrino Super Beam in conjunction with a megaton underground Water Cherenkov neutrino detector installed at a distance of about 500 km from ESS has been evaluated. In addition, the choice of such detector will extent the physics program to proton–decay, atmospheric neutrinos and astrophysics searches. The ESS proton linac upgrades, the accumulator ring needed for proton pulse compression, the target station optimization and the physics potential will be described.

In addition to neutrinos, this facility will also produce at the same time a copious number of muons which could be used by other projects as a muon collider. The ESS neutron facility will be fully ready by 2025 at which moment the upgrades for the neutrino facility could be decided.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 777419.

Keywords: ESSnuSB, neutrino, CP violation, neutrino oscillations, ESS