Leptonic CP-Violation with ESSνSB: Design and Simulations of the 4-Horn Target Station

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Based on the tiny differences in how matter and antimatter behave at the scale of elementary particles, known as charge-parity, CP-, violation, scientists believe that there is some subtle asymmetry between them, and that soon after the Big Bang, this led to a universe dominated by matter. The current problem is that not enough CP-violation has been observed, and that the Standard Model (SM) also does not predict enough to explain the observed asymmetry. The so-called “neutrino oscillations” phenomenon convincingly indicates that neutrinos do have mass, contradicting the SM hypotheses. Recent results from reactor experiments have shown that the third mixing angle, θ13 , is higher than its previously defined standard value, with a value of ~ 9°, opening a new window for discovering and measuring a nonzero value of the Dirac leptonic CP violating angle, δ_CP. Moreover, the T2K experiment has recently reported new results on the δ_CP, where they disfavored almost half of its possible values at the 99.7% (3σ) confidence. In the light of these new findings, an urgent need raised to improve the detection sensitivity of the current long-baseline detectors, with a key modification to place the far detectors at the second, rather than the first, oscillation maximum. Many of the presently planned detectors are the ones that use “intense” neutrino beams, such as DUNE in the USA, T2HK in Japan and ESSνSB in Europe. While the design of the US and Japanese experiments aim for measurement at the first-, the ESSvSB will measure at the second- oscillation maximum, leading to a significantly higher sensitivity to CP‐violation compared to the other two experiments. Several technological challenges must be precisely studied before addressing the design of the ESSνSB detector. Among these, the design and physics of the target station and the neutrino beam considered highest priority at this phase of the project. UHH represents Germany in the project, as an associate member, since September 2019. The strategic objective of this DFG-proposal is to continue and extend this unique contribution. This contribution will be continued within the neutrino group of the IEP-UHH. The specific objectives of the proposal are: 1- Optimization of the hadron-collector (horn) design in order to increase the charge current, CC, events at the detector, hence the neutrino beam characteristics; flux and profile. 2 -Perform full radiation, energy deposition and activation calculations in the different parts and shields of the ESSνSB target station. 3- Define the baseline design for the target station and its internal components, which will be introduced in the ESSνSB CDR at the end of phase-I, and later in the TDR.I strongly believe that continuing such involvement through the UHH in such unique project will undoubtedly reinforce the role that the German neutrino physics community, in general, and that of the UHH, in particular, plays, nationally and internationally, in this field.