Accelerator Neutrinos

Abstract:

The proposed Long Baseline Neutrino Observatory (LBNO) initially consists of $\sim 20$ kton liquid double phase TPC complemented by a magnetised iron calorimeter, to be installed at the Pyh\"asalmi mine, at a distance of 2300 km from CERN. The conventional neutrino beam is produced by 400 GeV protons accelerated at the SPS accelerator delivering 700 kW of power. The long baseline provides a unique opportunity to study neutrino flavour oscillations over their 1st and 2nd oscillation maxima exploring the $L/E$ behaviour, and distinguishing effects arising from $\delta_{CP}$ and matter. In this paper we show how this comprehensive physics case can be further enhanced and complemented if a neutrino beam produced at the Protvino IHEP accelerator complex, at a distance of 1160 km, and with modest power of 450 kW is aimed towards the same far detectors. We show that the coupling of two independent sub-MW conventional neutrino and antineutrino beams at different baselines from CERN and Protvino will allow to measure CP violation in the leptonic sector at a confidence level of at least $3\sigma$ for 50\% of the true values of $\delta_{CP}$ with a 20 kton detector. With a far detector of 70 kton, the combination allows a $3\sigma$ sensitivity for 75\% of the true values of $\delta_{CP}$ after 10 years of running. Running two independent neutrino beams, each at a power below 1 MW, is more within today's state of the art than the long-term operation of a new single high-energy multi-MW facility, which has several technical challenges and will likely require a learning curve.

Abstract:

A simultaneous beam and atmospheric oscillation analysis that combines the T2K and SK experiments has been presented. The first sensitivities of the joint analysis are reported, with the intention for the two collaborations to publish a data analysis in the near-future. This analysis leverages the different energies and baselines of the two experiments and provides strong sensitivities on δCP, sin2(θ23) and ∆m232. To do this, a Bayesian Markov Chain Monte Carlo technique is utilised to generate parameter estimates and credible intervals. Constraints from the T2K near detector are also used to constrain the uncertainties of both beam and atmospheric predictions.

For a known set of oscillation parameters close to the preferred values from a T2K-only data fit, the sensitivity of the joint analysis to sin2(θ23) is increased compared to the beam-only analysis, illustrated by a 7% reduction in the width of the 1σ credible interval. Furthermore, the sensitivity of the joint analysis to select the correct mass hierarchy hypothesis is drastically improved compared to the beam-only analysis, culminating in a substantial preference as classified by Jeffrey’s scale. This statement is stronger than the sensitivity of the beam-only analysis, either with or without external constraints on sin2(θ13). The sensitivities of the beam-only and joint beam-atmospheric analyses have also been compared for a known set of oscillation parameters which are CP-conserving. The joint analysis displays an improved ability to select the correct phase of δCP and octant of sin2(θ23) compared to the beam-only analysis. This thesis illustrates the benefit of the combined beam and atmospheric analysis, which could also be extended for use in the next-generation Hyper-Kamiokande experiment.