Ｔ２ＫとＳＫ実験データの組合せによるニュートリノ質量とミキシングパラメータの制限

2014 Fiscal Year Annual Research Report

• Project/Area Number: 14F04796
• Research Institution: The University of Tokyo
• Principal Investigator: MARTENS Kai 東京大学, カブリ数物連携宇宙研究機構, 准教授 (20535025)
• Co-Investigator(Kenkyū-buntansha): CALLAND Richard 東京大学, カブリ数物連携宇宙研究機構, 外国人特別研究員
• Project Period (FY): 2014-04-25 – 2017-03-31
• Keywords: Sensitivity studies / neutrino oscillation / hyper-kamiokande study

Outline of Annual Research Achievements

In order to quantitatively gauge the sensitivity of improvements to the Super-Kamiokande atmospheric oscillation analysis, the current analysis method was implemented into the existing framework used for T2K oscillation analyses. This means that the data from both experiments can now be consistently studied. Following from this, I performed a series of sensitivity studies using Monte Carlo simulation to probe which areas of the detector reconstruction could have more impact if they were improved. It was determined that improvements to multi-ring events in the ～10 GeV region would yield a stronger signal to CP violation. A profile likelihood method was developed to produce fast results with the study framework, whilst allowing for conservative estimations for systematic uncertainties. Some basic Bayesian analyses were also performed to validate the method. Also, the oscillation probability calculations were ported to GPU, allowing for an event-by-event reweighting method to be feasibly used. In addition to Super-Kamiokande, I also used the framework to produce sensitivity studies for the proposed Hyper-Kamiokande and nuPRISM detectors, which helped to determine the feasibility of using the proposed detectors for similar atmospheric measurements done with Super-Kamiokande.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

I believe that the progress made so far is good and that there is momentum to carry the project forward. Critical steps have been made towards the goal of improving the sensitivity of both T2K and SK to CP violation. The major achievement would be the combining of the analysis frameworks, to use the more modern and flexible T2K framework. This means that already the data can be analysed together, however the next major task would be to both improve the reconstruction of SK and to reassess the SK systematic uncertainties such that they can be combined with T2K, thus further constraining the errors. The improvement of the reconstruction is important as currently there is much more data collected by SK that contains information that we have yet to extract. The improvements to the multi-ring reconstruction will allow us to use this information in the analysis, and will improve the sensitivity to CP violation by a non-negligible amount.

Strategy for Future Research Activity

As stated, the plan going forward is to improve the SK reconstruction, specifically targeting the multi-ring region around 10 GeV in energy. The plan for this is to develop a new method for ring counting, based on a non-parametric mixing model. This is in contrast to the piecewise optimization method currently used, which is both slow and doesn’t provide a credible way to compare ring hypotheses. The mixing model method will allow the reconstruction of multiple rings to be performed in a Bayesian way, meaning that we can report degrees of belief (probability) about what kinds of rings are found and how many we saw, along with the vertex information. I expect this to be a big contribution to the reconstruction software. Once the new reconstruction is working, the systematic uncertainties can be reevaluated and the full data analysis can be performed.