Analysis of the single $\pi^+$ production in neutrino neutral current interactions and instrumentation developments for the future understanding of neutrino physics using the ND280 detector of the T2K experiment

Nowadays, one of the most active research fields within the domain of high energy physics is the study of neutrinos. In the mainstream theory, encompassed in the Standard Model (SM) of particle physics, the phenomenology of neutrino physics is determined by seven degrees of freedom, consisting of three masses (m1,m2,m3), three mixing angles (.12, .13, .23) and a CP-violating phase (dCP). Currently, the most prominent experimental challenge in neutrino physics is to determine precisely the values of these parameters in order to better understand the fundamental behavior of nature and to to explore the validity of the SM. The Tokai-To-Kamioka (T2K) experiment is one of the main references in the field. In T2K an accelerator-based neutrino or antineutrino beam is produced and measured at two sites: At 280 m from the production point using the ND280 detector and 295 km away in the Super-Kamiokande detector. ND280 is used to characterize the properties of the neutrino beam before any significant oscillation effects take place and to study how neutrinos scatter in matter at energies relevant to T2K. With this knowledge, an event rate prediction is calculated for Super-Kamiokande that in combination with data is used to measure neutrino properties, in particular .13, .23, m223 = m22 - m23 and dCP. Two factors limit more accurate measurements in T2K. On one hand, the limited number of collected neutrino events determines the amount of statistical error. On the other hand, event rate predictions are affected by systematic uncertainties regarding the detector, beam, and neutrino interaction models. While the statistical error will decrease in the coming years as T2K continues to collect data, active work is needed to reduce systematic uncertainties. In this thesis two ways to achieve it are studied consisting of analysis and instrumentation developments. In T2K’s oscillation analysis (OA) one of the main sources of systematic uncertainty is that of neutrino neutral current interactions that produce a single p+ in the final state (NC1p+). Current knowledge about this process is limited due to the fact that the only reported measurement consists of less than hundred interactions recorded in 1978 by the Gargamelle bubble chamber experiment. In this thesis, the first study of this type of interactions in a modern neutrino experiment is presented using T2K data collected by the ND280 detector. With this purpose, a new selection algorithm for ND280 data has been developed. The preliminary analysis of the output selected samples constitutes the most detailed description of the nature of this process. In addition, the extracted cross section uncertainty is less than half of that currently used in T2K OA and thus has the potential to significantly benefit future T2K oscillation measurements. Improving existing instruments is an essential task to reduce systematic uncertainties. To this end, the ND280 detector is being significantly upgraded with the addition of three new detection technologies: two new High-Angle TimeProjection-Chambers (HATPCs), a novel fully Super-Fine- Grain-Detector (SuperFGD) and six Time-Of-Flight (ToF). In this thesis, relevant contributions to the development of these technologies are presented, including: simulation-based sensitivity studies, validation tests of the novel ERAM-based readout of the HATPCs, measurements of the response and the PID potential of SuperFGD using prototype data and the development of new deep learning reconstruction methods for SuperFGD and the ToF panels.

Neutri
Neutrino
Ciències Experimentals
53
neutrino/mu: secondary beam
antineutrino/mu: secondary beam
neutrino: oscillation
pi+: neutrinoproduction
phase: CP
neutrino: mass difference