Resumo: Neutrinos are some of the most abundant and least interacting elementary particles in the Universe. They are leptons with zero electric charge, spin 1/2 and very small mass, and exist in three known active flavors – electron, tau and muon. Despite being theorized in 1930 and discovered in 1956, a number of fundamental questions about them remain unanswered, such as: What are the values of the masses of each of the flavors? Are neutrinos their own antiparticles? Do other neutrino flavors exist? These questions and the multitude of phenomena involving neutrinos are what drive Neutrino Physics, a field that have been awarded three Nobel prizes in the last 25 years. The coherent neutrino-nucleus scattering (CE(ni)NS) is a process whereby a neutrino scatters off an atomic nucleus via neutral-current (weak) interaction; its cross section is proportional to the square of the number of neutrons in the nucleus and the square of the energy of the neutrino. This scattering covers a wide range of phenomena, and the understanding of its nature is useful to many areas of physics, from the existence of a new sterile neutrino flavor to the search for Dark Matter candidates. But even with the cross section enhancement provided by coherence, the energies for CE(ni)NS are very low, requiring detectors with good sensitivity and a well characterized low background. The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) is the first experiment to apply the CCD imaging sensors to neutrino detection. Installed in and using electron antineutrinos from a
Brazilian nuclear reactor, the detector is built for the measurement of nuclear recoils from CE(ni)NS with energies lower than 10 eV. Since the detector produces digital images as output, the processing of these images is an essential step in the data analysis and can limit our capability of measuring the coherent scattering. Thus, CONNIE has developed its own image processing pipeline for that
matter. In this work we present an independent pipeline for processing the CONNIE images. It is based on SExtractor, a widely used free software for processing astronomical images, and a number of new tools we developed and made available to the collaboration. The new pipeline was capable of reproducing the spectrum obtained with the standard pipeline. This attested the robustness of both the CONNIE and the new procedures, and showed that the spectra are essentially independent of the pipeline used. Based on the new pipeline, we implemented a methodology for assessing the efficiency and contamination in the identification of (simulated) neutrino events. We then applied this methodology to test whether parameters derived from a fit to an event’s shape are helpful for separating neutrinos and spurious detections. Lastly, we applied cuts in these morphological parameters and were able to improve the contamination of our detections. |
