Neutrino Physics at ESS and the upgrades needed for the ESSnuSB

The European Spallation Source (ESS) in Lund, Sweden, will provide, by 2023, the world's most powerful neutron source. The 2 GeV ESS linac will provide 5 MW protons. The total power of the linac can be raised to 10 MW by increasing its pulse frequency, thus making possible the production of, in addition, a very intense, 0.4 GeV neutrino Super Beam, ESSnuSB. Search for leptonic CP violation at the second oscillation maximum, where the sensitivity is about 3 times higher than at the first, would be possible at 5 sigma significance level in 56 % (65 % with an upgrade to 2.5 GeV beam energy) of the leptonic CP-violating phase range after 10 years of data taking. 5 % systematic error in the neutrino flux and 10 % in the neutrino cross section are assumed. The outstanding physics reach possible with ESSnuSB and the upgrade of the ESS accelerator complex needed for ESSnuSB will be discussed in the paper.