Likelihood based reconstruction algorithm for finding short tracks within the T2K experiment's fine grained detector

Abstract

The T2K experiment is a long baseline neutrino experiment. Rates of different types of neutrino interactions are compared at a near detector and a detector 295 km from the neutrino source which enables neutrino oscillation and cross-section measurements. Understanding the activity near the neutrino interaction vertex in the near detector is crucial to identifying how a neutrino interacted. Current reconstruction algorithms for T2K's Fine Grained Detectors (FGD) have a decreased sensitivity to short tracks (<200mm) such as those created by low energy protons and pions. A new likelihood based reconstruction algorithm entitled FLikFit (FGD Likelihood Fitter) has been written that uses information from the deposited charge and the position of the hits within the FGDs in an attempt to tag these particles. It traces a predicted path of the particle through the detector and calculates expected kinetic energy and path length values which are fed to an existing probability distribution function to obtain a likelihood for each scintillator bar. The fitter is seen to calculate likelihoods effectively and proves to be adept at hypothesis testing, but further development is required to improve the FLikFit's ability to converge.