Estimating detector systematic uncertainties for the T2K far detector

TL;DR

This paper presents an advanced method for estimating systematic uncertainties in the Super-Kamiokande detector used in the T2K neutrino oscillation experiment, improving the accuracy of oscillation parameter measurements.

Contribution

It introduces a comprehensive MCMC-based procedure for quantifying detector systematic uncertainties, including new systematics for additional analysis samples, enhancing the precision of the T2K analysis.

Findings

540-dimensional MCMC fit achieved

Improved uncertainty quantification for new samples

Enhanced accuracy in neutrino oscillation parameters

Abstract

Tokai to Kamioka (T2K) is a long-baseline neutrino oscillation experiment that measures oscillation parameters related to both $\nu_\mu(\bar{\nu}_\mu)$ disappearance and $\nu_e(\bar{\nu}_e)$ appearance in a $\nu_\mu(\bar{\nu}_\mu)$ beam. T2K uses Super-Kamiokande (SK) as its far detector, and SK detector systematic errors are currently among the leading sources of systematic uncertainty in the T2K oscillation analysis. Therefore, accurate understanding of detector mis-modelling and event reconstruction uncertainties in SK is crucial to the extraction of the neutrino oscillation parameters. The detector error estimation procedure quantifies uncertainties by fitting SK atmospheric MC to data in a Markov Chain Monte Carlo (MCMC) framework. Uncertainties are separated based on true event topology above Cherenkov threshold in the SK atmospheric MC in order to capture how the uncertainties should affect the different signal and background samples when propagated to the T2K beam oscillation analysis. The procedure has been upgraded for the upcoming analysis cycle to include systematics targeting newly added $\nu_eCC1\pi^\pm$ and $NC\pi^0$-enhanced analysis samples, among other changes, culminating in a 540 dimensional MCMC fit between atmospheric MC and data in SK. The far detector analysis chain and its integration into the broader T2K oscillation analysis will be discussed in these proceedings.