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A study of ν µ-induced charged current (CC) π+ production at the T2K off -axis near detector (ND280) is presented. Using Monte Carlo (MC) data studies event selections for both CC-inclusive and enriched CC- π+ samples have been developed using the ND280 tracker-region and surrounding ECals. Two types of CC- π+ selections were developed - one using the TPC to identify the pion and the other using a new ECal PID based on the deposited charge per unit length. Data/MC ratios are calculated and compared with the associated detector, neutrino interaction and flux simulation systematics. The predicted neutrino interaction rate was based on v2.6.2 of the GENIE MC generator and on T2Ks tuned 11a JNUBEAM flux simulation. The data used was collected between Nov. 2010 and March 2011 during the Run 2 data taking period and corresponds to a total integrated POT of 7.83 x 10[to the power of 19]. For the ν µ-CC-Inclusive selection which selects ν µ -CC interactions with a purity of 88:1% we find: [Mathematical formulae appear here. To view, please open pdf attachment] These show that the current measured and predicted rates for both the inclusive rate of ν µ neutrino interactions and those with at least one π+ in the final state agree to within the systematic uncertainties associated with neutrino interaction and flux simulation. Moreover, these selections lay the groundwork for future analyses, using larger data sets, that can be used to constrain these sources of uncertainty.

The discovery of neutrino oscillations provides evidence that the Standard Model neutrinos have mass. Many models generate the mass for the light neutrinos by postulating the existence of heavy neutrinos. This thesis presents the search for a heavy Majorana neutrino decaying into a W boson and a muon that was performed using the ATLAS detector at the LHC. The search is performed using final states with two same-sign muons, two or more high momentum jets and low missing transverse energy. The events are required to pass the ATLAS muon trigger and the improvements made in the muon trigger algorithms are also presented. The data used in this thesis were collected using pp collisions at sqrt(s) = 7 TeV in 2011 and correspond to an integrated luminosity of 4.7 fb−1. In the search no excess of events above the background prediction is observed and 95% confidence level upper limits are set on the cross section times branching ratio for the production of heavy Majorana neutrinos. Limits are set for heavy Majorana neutrinos with masses ranging from 100 to 300 GeV, in which the observed limits range between 28 to 3.4 fb. These are most stringent direct limits to date for heavy neutrino masses larger than 100 GeV.

This thesis measures the muon neutrino oscillation at T2K using the first data of the experiment. It concentrates on developing an original selection at Super-Kamionde, the T2K far detector, that improves the performance of the current standard selection. A new, more precise measurement of the oscillation parameters sin2 2 23 and Δm2 32 is performed using this new selection. T2K is a long-baseline neutrino oscillation experiment located in Japan which began data taking in January 2010. It uses the world’s most powerful accelerator generated beam of muon neutrinos intersected by two detectors. The near detector is located 280 m from the beam source while Super-Kamiokande lies 295 km away. Super-Kamiokande is a 50 kt water Cherenkov detector which measures the neutrino beam after oscillation. The determination of the oscillation parameters comes from looking at the disappearance of muon neutrinos from the beam. For this purpose event selection at Super-Kamiokande is optimised for neutrino flavour identification and energy reconstruction, specifically, selecting muon neutrino charged-current quasi-elastic events, primarily with single muon-like Cherenkov rings produced by the outgoing muon. This thesis evaluates two new methods of enhancing the selection to obtain a higher sensitivity from the data, firstly by exploring a multi-variate analysis approach to charged-current quasi-elastic selection, and secondly through the exploration of an additional charged-current single charged pion channel. Out of these only the multivariate based selection produced an improvement in the sensitivity to oscillation with respect to the standard selection. A first analysis of the data collected until March 11th 2011 using the above described improvement is presented in this thesis. A value of 2:68+0:12 −0:18 × 10−3 eV2 was recorded for Δm2 32 and 0:999+0:001 −0:009 for sin2 2 23. 2

The existence of neutrino oscillations demands that neutrinos have non-zero rest mass, the evidence for and implications of which are discussed. Nuclear B-decay is offered as a model-independent tool for direct neutrino mass measurement and contemporary experimental measurements are reviewed. The AMBER experiment is introduced as a novel charge spectrometer, aimed at precision electron energy measurements to probe the structure of the B-spectrum close to its endpoint. AMBER employs a vacuum insulated inverse Kelvin probe to continuously monitor a single rate-of-change observable. A detailed technical description of the technique is provided, followed by proof of principle demonstrations and an examination of hardware performance and its capability to provide sub-eV electron energy resolution. a first order B-spectrum reconstruction algorithm is described and applied to data from a Monte Carlo simulation of a highly idealised AMBER-like model experiment, in which important source scattering effects are neglected, and a calculation of the sensitivity to the neutrino mass is made. Finally the successes and shortcomings of the AMBER technique are discussed.

Neutrino mixing is a thriving area of particle physics research, with the recent discovery of non-zero θ13 inspiring a large amount of research into the field. This thesis presents two models which aim to explain the observed neutrino mixing patterns in the context of Grand Unified Theories, which also output quark masses and mixings. A model predicting Tri-Bimaximal mixing is presented which combines a previously published SU(5) model with an A4 family symmetry. Extra adjoint fermionic matter is present as prescribed by the original Unified model, and this provides 2 seesaw particles; however they are constrained to give the same contribution to neutrino mixing once the flavour symmetry is imposed. This motivates the addition of an extra field in order to obtain two non-zero neutrino masses. This model has the desirable property of having a diagonal Majorana sector, something which is normally assumed in such models. In order to explain the discovery of non-zero θ13, a second model is presented which produces Tri-Maximal mixing, a perturbed version of Tri-Bimaximal mixing which retains the solar prediction whilst changing the atmospheric and reactor predictions. This is also performed in a unified context and therefore charged lepton corrections to mixing are related to the Cabibbo angle in a new way via a sum rule. Finally the impact of flavour symmetries on leptogenesis is discussed; it is mentioned that models which predict neutrino mixing can very often lead to 0 leptogenesis and therefore no baryon asymmetry in the Universe. However this conclusion is drawn without considering the difference in scales between flavour symmetry breaking and leptogenesis. When this is taken into account it is shown in the context of two simple models that successful leptogenesis can be achieved.

The SNO+ experiment will use a liquid scintillator based detector to study solar, geo, and reactor neutrinos and double beta decay. This thesis discusses the effect of backgrounds on the measurement of neutrinoless double beta decay and describes analysis techniques developed to reduce their impact. Details of the modeling of the photomultiplier tubes in the SNO+ Monte Carlo RAT are first described and comparisons are made with the SNO Monte Carlo SNOMAN. SNOMAN has been extensively verified with calibration sources and RAT is shown to be in good agreement. The event reconstruction techniques are then presented and predict an achievable 15cm position and 7% energy resolution. The backgrounds are discussed and pileup backgrounds identified, including many previous unknown pileup backgrounds. Techniques to reject the pileup background are presented and shown to give over 99% rejection in the region of the double beta decay end point (3-4MeV), below the irreducible background from solar neutrinos. Finally the resulting limit on the effective Majorana neutrino mass SNO+ could achieve in 2015 is predicted to be 270meV and this is compared with other experiments that are underway.