Identification of neutrino oscillations in the MINOS detector Daniel Cole

Aims Use likelihood methods to investigate separation of CC muon neutrino events from background of NC and electron neutrino events. Focus on improving separation of low energy (<2GeV) neutrino events.

Code MC beam neutrino events (generated at Cambridge using NuMI low-energy beam (PH2LE) flux file) 4/5 data used to generate PDFs of 3 variables 1/5 data used as sample DetSim Cambridge demultiplexer Cambridge Standard Reconstruction Analysis

Formation of the Likelihood i) track strips / total strips ii) track pulse height per track plane iii)track planes For each event in sample: p cc = p cc1 ×p cc2 ×p cc3 p nc = p nc1 ×p nc2 ×p nc3 i) ii) iii)

Standard Likelihood Standard likelihood: efficiency = CC events above PID threshold / total CC events purity = CC events above PID threshold / total events above PID threshold

Super-K Likelihood Attempt to reproduce David Petyt’s results using likelihood based on S-K analysis: S-K likelihood: Improvement due to updated reconstruction code

Likelihood Function Comparison Comparison of standard and Petyt’s likelihood functions (using SR): Little difference in performance. Standard likelihood used from now on. Attempt to develop analysis…

Track Plane Cut First new cut: any events with ≥60 track planes must be CC so put into likelihood at PID = 1 Negligible gain in efficiency but pre- likelihood cut simplifies the procedure

Comparison of Reco Algorithms Comparison of SR and Cambridge (AtNu). reconstruction codes (using the track plane cut):

Visible Energy Comparison CC: visible energy = true neutrino energy NC: visible energy = true hadronic energy Sample split into 4 visible energy ranges: energy < 2GeV energy = 2-5GeV energy = 5-10GeV energy > 10GeV

Low Energy Events <2GeV visible energy range performs poorly due to low number of reconstructed tracks and high background. Sample of <2GeV events generated and added to previous data. Define: reconstructed energy = reconstructed track energy + reconstructed hadronic energy New set of PDFs constructed from low reconstructed energy events only. Previously used all events.

PDFs for Low Energy Events New set of variables: i) ii) iii) i) track strips / total strips ii)track planes iii)reconstructed track velocity (Also tried: i)track pulse height per track plane ii)track end plane – shower vertex end plane) Further cut: events with track end plane - shower vertex end plane ≥40 identified as CC.

Separation of Low Energy Events original variables, all events used in PDFs new variables, all events used in PDFs new variables, only low reconstructed energy events used in PDFs 5% improvement in efficiency at 95% purity for low energy events – but even better at higher purities.

Conclusions used new likelihood separated events by reconstructed energy chose suitable variables for energy range (for low energy events: i) track strips / total strips ii) track planes iii) reconstructed track velocity) performed pre-likelihood cuts when: track planes ≥60 track end plane - shower vertex end plane ≥40 achieved improvements in signal separation