INVITED SPEECH: ESSnuSB - a neutrino Super Beam based on the use of the 5 MW ESS linac

FULL TITLE:
ESSnuSB - a neutrino Super Beam based on the use of the 5 MW ESS linac exploiting the higher discovery potential for leptonic CP violation at the second neutrino oscillation maximum

Abstract
Very intense neutrino beams and large neutrino detectors will be needed to enable the discovery of CP violation in the leptonic sector. The proton linear accelerator of the European Spallation Source (ESS), currently under construction in Lund, Sweden with a foreseen start of operation in 2022, can be made to provide, in parallel with the spallation neutron production, a very intense, cost effective and high performance neutrino beam. The proposal presented here is to upgrade the ESS accelerator average power from 5 MW to 10 MW by raising its duty cycle from 4% to 8% and use the extra 5 MW power to produce a Super Beam of average neutrino energy 0.4 GeV. A long baseline experiment using the so produced Super Beam and a megaton underground Water Cherenkov detector located at the second neutrino oscillation maximum 540 km from Lund, ca 1 km underground in the Garpenberg mine, will make it possible to discover leptonic CP violation at 5 sigma significance level in more than 50% of the leptonic Dirac CP-violating phase range. This high performance can be obtained with ESSnuSB assuming a systematic measurement uncertainty level of ca 7%, which, judging by available experience in the field, is a realistic assumption. In contrast, to attain a similar performance with experiments planning to collect most of their event statistics at the first oscillation maximum, one needs to assume that a systematic measurement uncertainty level of ca 2-3% can be attained - the realism of which remains to be proven. The reason for the higher sensitivity with ESSnuSB is that the variation of the CP-angle signal at the second oscillation maximum is about three times higher as compared to that at the first. The ESSnuSB detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation are presented. The presentation will describe the proposed facility and the physics that would be possible with this experiment.