NEUTrino OscillatioN analysis at T2K and SuperKamiokande experiments: Can neutrinos explain the matter-antimatter asymmetry in the Universe?

Project Information

NEUTON

Grant agreement ID: 839481

DOI

10.3030/839481

Project closed

EC signature date 29 March 2019

Start date 1 September 2019

End date 31 August 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 271 227,84

EU contribution

€ 271 227,84

Coordinated by

UNIVERSIDAD DE SEVILLA
Spain

Periodic Reporting for period 2 - NEUTON (NEUTrino OscillatioN analysis at T2K and SuperKamiokande experiments: Can neutrinos explain the matter-antimatter asymmetry in the Universe?)

Reporting period: 2021-09-01 to 2022-08-31

Summary of the context and overall objectives of the project

The NEUTON project is aimed at getting a better knowledge of the neutrino oscillation phenomena in long-baseline neutrino oscillation facilities. The success of these studies and experiments is of paramount relevance for the understanding of the evolution of the Universe among other open questions in Science.

'Why the Universe is primarily comprised of matter today, instead of equal parts of matter and antimatter', is one of the most intriguing questions in all of science. In spite of its tremendous success, the Standard Model (SM) of elementary particles does not fully answer several fundamental questions, which require to be investigated with various complementary approaches and using different “messenger” particles, such as the elusive neutrinos. In particular, the SM assumes charge-parity (CP) symmetry which involves that production and decay rates of particles and antiparticles should be equivalent; but such situation would have led to an empty cosmos shortly after the Big Bang. So, what CP-violating (CPV) process beyond the SM favoured the production of matter over antimatter? The answer could lie in the recent discovery of neutrino oscillations, which has glimpsed the possibility that neutrinos and antineutrinos behave differently, opening the door to new physics beyond the SM. This has motivated several experiments (FermiLab [USA]: NOvA, MINERvA, DUNE; Japan: T2K and SuperKamiokande (SK)) aimed at determining neutrino oscillation parameters and CPV as well as other open questions in Physics such as dark matter search through sterile neutrinos, proton decay or supernovae analysis.

Nevertheless, the success of current and forthcoming neutrino oscillation experiments largely depends on an accurate description of neutrino interactions, where the determination of neutrino-nucleus cross sections is one of the leading experimental uncertainties. The current precision on the modelling of these cross-section at the level of 10% are by far too large for the precision expected by the next generation of experiments (< 5%). In this sense, the neutrino interaction models developed by the University of Seville group would help to improve this analysis as they provide an accurate description of neutrino cross-section data in a broad energy range, being a promising candidate to be implemented in the T2K and SK neutrino event generators. This would improve the experimental systematics needed to answer the above mentioned open questions as well as to shorten the required running time and experimental costs of current and next-generation neutrino experiments (DUNE and HyperKamiokande).

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work performed during the project has addressed the following topics:

- Using relativistic mean field (RMF) and superscaling (SuSAv2) models, several T2K and SK data have been studied with the aim of analyzing low-energy nuclear effects and improve data analysis. Unlike other models, we have found important differences between carbon and oxygen at these kinematics, in accordance with some T2K data.

- The RMF and SuSAv2 codes has been adapted and optimized to implement them in the NEUT event generator. After the full implementation, the RMF and SuSAv2 models will be used directly for the oscillation analysis and the determination of oscillation parameters.

The project has been carried out in collaboration with ICRR, T2K and SK members: S. Dolan, Y. Hayato and others; and also with researchers from the University of Seville, Turin, Granada and Complutense of Madrid. Guillermo D. Megias has got involved in regular bi-weekly meetings with different T2K working groups: NIWG (Neutrino Interaction Working Group) and XSEC WG (Cross Section Working Group), where details of the project have been regularly discussed.

Within this project we have obtained the most accurate comparison with T2K neutrino cross-section measurements, showing a large improvement with regards to other models. We have also extended the SuSAv2 and RMF models to analyze neutrino reactions on argon, an asymmetric nucleus, observing a good agreement with recent semi-inclusive measurements.

Guillermo D. Megias has also taken shifts on the T2K and SK facilities. These shifts are focused on real-time diagnosis and basic trouble-shooting of the beam operation, data acquisition or detector activity. Guillermo Megias has also supervised and trained other new members of the collaboration.

A collaboration has been established with the NINJA group, a Japanese collaboration aimed to measure neutrino-water interactions using a nuclear emulsion detector. We have developed a semi-phenomenological model to analyze the resonance region in neutrino-nucleus reactions and in collaboration with the ICRR and the Univ. of Osaka we are adding high-energy nucleonic resonances in our models. Another collaboration with MIT and FermiLab has allowed to implement our models in their generators and to analyze electron scattering data which provide essential information for neutrino oscillation experiments. This collaboration has led to a publication in Nature.

This project has led to more than 20 publications (Nature, Phys. Rev. D, Astroph. Journal, PTEP, etc.), several contributions to international conferences and workshops (NEUTRINO2020, NuFact21, European Researcher’s Night 2020, etc.) and several media interviews.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The success of this project and of the current and forthcoming neutrino oscillation experiments largely depends on an accurate description of neutrino-nucleus interactions. The full implementation of our models in the experimental generators, which has started within this project and will continue in coming years, is expected to improve this analysis due to their accuracy on describing neutrino data. An innovative semi-inclusive reaction model has been developed to reduce nuclear-medium uncertainties by improving hadron detection efficiency. All this will shortly increase event-selection efficiency in T2K and SK while reducing interaction systematics by 2%. The research carried out in this project will be also relevant for the next-generation of neutrino oscillation experiments, DUNE (USA) and HyperKamiokande (Japan), where a complete determination of the CP symmetry violation and the neutrino-antineutrino oscillation differences is expected. This could lead to explain the matter-antimatter imbalance in the universe.

The success of this project is also fostering novel model-implementation techniques in neutrino generators with unprecedented reduction in computational time and straightforward extension to several nuclear targets. At the same time, the collaboration with the MIT and FermiLab (e4nu and CLAS collaborations) will continue in the following years for the analysis of electron-nucleus reactions of interest for oscillation experiments. This collaboration has led to a publication in Nature (2021) and two media interviews.

The development of sophisticated neutrino interaction models within this project has improved the description of neutrino interactions in oscillation experiments (T2K, MINERvA, etc.) and is expected to improve the above-mentioned experimental uncertainties as well as to shorten the required running time and experimental costs of current and next-generation neutrino oscillation experiments (DUNE and HyperKamiokande). The potential impact of all these outcomes in the society in general are mostly related to the scientific knowledge about the origin of the universe and the Big Bang.

Comparison of the SuSAv2-MEC model with recent data from the T2K experiment.