Roles of sterile neutrinos in particle physics and cosmology

The impacts of the light sterile neutrino hypothesis in particle physics and cosmology are reviewed. The observed short baseline neutrino anomalies challenging the standard explanation of neutrino oscillations within the framework of three active neutrinos are addressed. It is shown that they can be interpreted as the experimental hints pointing towards the existence of sterile neutrino at the eV scale. While the electron neutrino appearance and disappearance data are in favor of such a sterile neutrino, the muon disappearance data disfavor it, which gives rise to a strong appearance–disappearance tension. After a brief review on the cosmological effects of light sterile neutrinos, proposed signatures of light sterile neutrinos in the existing cosmological data are discussed. The keV-scale sterile neutrinos as possible dark matter candidates are also discussed by reviewing different mechanisms of how they can be produced in the early Universe and how their properties can be constrained by several cosmological observations. We give an overview of the possibility that keV-scale sterile neutrino can be a good DM candidate and play a key role in achieving low-scale leptogenesis simultaneously by introducing a model where an extra light sterile neutrino is added on top of type I seesaw model.

Latest Results from the T2K Neutrino Experiment

The T2K long baseline neutrino oscillation experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and anti-neutrino beams. This presentation reports on the analysis of our data from an exposure of 2 . 6 × 10 21 protons on target. Results for oscillation parameters, including the CP violation parameter and neutrino mass ordering, are shown.

Parallel Event Selection on HPC Systems

In their recent measurement of the neutrino oscillation parameters, NOvA uses a sample of approximately 25 million reconstructed spills to search for electron-neutrino appearance events. These events are stored in an n-tuple format, in 250 thousand ROOT files. File sizes range from a few hundred KiB to a few MiB; the full dataset is approximately 1.4 TiB. These millions of events are reduced to a few tens of events by the application of strict event selection criteria, and then summarized by a handful of numbers each, which are used in the extraction of the neutrino oscillation parameters. The NOvA event selection code is currently a serial C++ program that reads these n-tuples. The current table data format and organization and the selection/ reduction processing involved provides us with an opportunity to explore alternate approaches to represent the data and implement the processing. We represent our n-tuple data in HDF5 format that is optimized for the HPC environment and which allows us to use the machine’s high-performance parallel I/O capabilities. We use MPI, numpy and h5py to implement our approach and compare the performance with the existing approach. We study the performance implications of using thousands of small files of different sizes as compared with one large file using HPC resources. This work has been done as part of the SciDAC project, “HEP analytics on HPC” in collaboration with the ASCR teams at ANL and LBNL.

Results from the NOvA Experiment

The NOvA experiment is a long-baseline accelerator-based neutrino oscillation experiment. It uses the upgraded NuMI beam from Fermilab to measure electron-neutrino appearance and muon-neutrino disappearance between the Near Detector, located at Fermilab, and the Far Detector, located at Ash River, Minnesota. The NuMI beam has recently reached and surpassed the 700 kW power benchmark. NOvA’s primary physics goals include precision measurements of oscillation parameters, such as [Formula: see text] and the atmospheric mass-squared splitting, along with probes of the mass hierarchy and of the CP violating phase. This talk will present the latest NOvA results, based on a neutrino beam exposure equivalent to [Formula: see text] protons-on-target.