The European Spallation Source neutrino Super Beam, ESSnuSB, is a particle physics long-term project investigating about Charge-Parity Violation in the leptonic sector to understand the matter-antimatter asymmetry in the Universe. It is supported by two Design Studies, ESSnuSB/ESSnuSB+, financed by the European Commission. It is composed of 20 participating institutes/organisations from  11 countries.

The project was initiated by the COST networking Project titled: “EuroNuNet“. The activities of both projects, ESSnuSB and EuroNuNet are tightly intertwined.

Background

After the Big Bang, matter and antimatter were produced in equal quantities through materialisation of the huge energy released. Observations show that today, however, there is a nearly total absence of antimatter in the Universe. The occurrence of Charge-Parity Violation (CPV) is a necessary condition for an explanation of this absence. CPV has already been observed in the quark sector but the measured amount is insufficient to explain the observed matter-antimatter asymmetry. Recent neutrino oscillation measurements indicate that the discovery of neutrino CPV becomes an important candidate to explain the observed matter dominance in the Universe. The goal of ESSnuSB project is to discover and measure neutrino CPV with unprecedented sensitivity. The ESSnuSB concept takes advantage of two outstanding opportunities:

1. The first is the construction in Europe of the European Spallation Source, ESS, the world’s most intense proton source, with a beam power almost one order of magnitude higher than any other accelerator.
2. The second is the measured unexpectedly large value of the oscillation mixing angle θ13. The latter fact implies that to obtain maximum sensitivity, the neutrino detector shall be placed at the second neutrino oscillation maximum, not at the first as implemented by the other proposed experiments. The Zinkgruvan mine in Sweden, in which it is proposed to install the underground neutrino detector, is situated at a distance from ESS that corresponds to the second maximum.

The goal of the ESSnuSB H2020 Design Study was to organise European physicists and accelerator engineers in cooperation with the ESS Laboratory to study and produce a Conceptual Design Report (CDR) for the ESSnuSB project including the physics performance of the project. This project took place between 2018 and 2022. The CDR can be found here. The ongoing Horizon Europe project ESSnuSB+ which started beginning of 2023 and will finish end of 2026, has been proposed to perform complementary studies to prepare the ground for ESSnuSB. This second Design Study, ESSnuSB+, investigates the possibility to measure with accuracy the neutrino cross-sections relevant to this research project and perform sterile neutrino searches. ESSnuSB+ will also perform civil engineering studies for the implementation of the facility in the ESS site and the implementation of the far detector near Zinkgruvan mine.