Session M4: Neutrino Physics and Searches

New Paradigm for the Analysis of Three Neutrino Oscillation Data: Hierarchy

A new approach to the analysis of neutrino oscillation data, with CP = 0, is proposed. A four fold symmetry exists for vacuum oscillations with $\theta_{13} = 0$. For $\theta_{13}\ne 0$, the four fold symmetry breaks into two two-fold symmetries given by the change in hierarchy and a change in the sign of $\theta_{13}$. Matter effects break this symmetry. We perform a global data analysis that maintains the four independent solutions. We find the oscillation probability $\mathcal{P}_{\mu\mu}$ breaks the symmetry at a level that is not insignificant. The largest symmetry breaking arises from $\mathcal{P}_{\mu e}$. The mixing parameters for each of the four solutions are quite similar to those found by others for positive $\theta_{13}$, the case studied by them. The best fit solution is for the normal hierarchy, positive $\theta_{13}$ case with a probability of 58.6\% that it is the correct result of the four possible cases. The second best fit is inverse hierarchy and negative $\theta_{13}$, the symmetry partner of the best fit, with a probability of 27.9\%. The probability that $\theta_{13}$ is positive is found to be 64.9\%, and the probability that normal hierarchy is correct is 65.8\%. Preliminary CP-violating results will be presented.   

Search for invisible nucleon decay in SNO$+$ during commissioning phase

The SNO$+$ experiment aims to explore several topics in neutrino physics, including neutrinoless double beta decay and low energy solar neutrinos. For its initial commissioning phase, SNO$+$ will fill its inner vessel with light water and run to evaluate the performance of the detector and electronics. During this water-fill phase, it will have a unique sensitivity to certain modes of invisible nucleon decay, where the nucleon decays to a mode in which the decay products are not detected, e.g. to 3 neutrinos. With just a couple of months of water running, SNO$+$ is expected to set an improved model independent limit on the current bounds.   

Search for heavy Majorana neutrinos in same-sign dilepton final states in pp collisions at $\surd $s$=$ 8 TeV with CMS detector

With the discovery of neutrino oscillations, the non-zero mass of the neutrinos has been confirmed. With this confirmation, a search for a mechanism to explain the non-zero mass of neutrinos has become popular among particle collision experiments such as the Large Hadron Collider (LHC) at CERN, the world's largest particle accelerator. The Compact Muon Solenoid (CMS), one of the general-purpose detectors of the LHC, is gathering data to measure the energies of the particles such as hadrons, leptons, jets, and photons produced by the proton-proton collisions at very high energies. In this presentation, we briefly explain the current status of a search for heavy Majorana neutrinos, one possible mechanism to explain the massive nature of the known neutrinos. The data used in this analysis correspond to an integrated luminosity of 19.7 fb$^{-1}$ of pp collisions at a center of mass energy of 8 TeV, comes from the data collected with the CMS detector during the 2012 operation of the LHC. In this work, the same sign leptons are found with the decay products of an accompanying W boson. Specifically W decays into two jets are considered.   

A Search for Lorentz Violation in the T2K Near Detectors

Lorentz symmetry violation (LV) arises when the behavior of a particle depends on its direction or boost velocity. This fundamental symmetry violation is expected to occur at the Planck scale (\(\sim 10^{19}\) GeV). The Standard Model Extension (SME) is a general theoretical framework that includes both General Relativity and the Standard Model while also allowing for the spontaneous breaking of Lorentz symmetry through a set of coefficients. As predicted by the SME, neutrinos couple to a background tensor field and can exhibit LV behaviors due to a sidereal time dependence in the neutrino oscillation probabilities. Time-dependent perturbation methods are used to extract the LV neutrino oscillation probabilities in the SME at baselines shorter than the neutrino oscillation length. A search for LV at the T2K near detectors with baselines of 280 m is presented. A Fast Fourier Transform analysis of the T2K data using the protons on target normalized neutrino event rate at the T2K near detectors is used to search for LV. A binned log-likelihood fit is performed to extract limits on the relevant SME coefficients or, in the case of LV detection, extract the values of the SME coefficients.   

Features in the energy and time distributions of neutrinos from a supernova burst and their detection with a multi-kiloton liquid argon detector

A multi-kiloton underground liquid argon detector will be an invaluable tool for investigating supernova bursts, recording thousands of neutrinos from a supernova event at $10~\textrm{kpc}$ in a $40~\textrm{kt}$ configuration. In this talk we explore the capacity of such a detector to observe various core-collapse-related physics signatures. We examine the time and energy resolutions required to distinguish features in the neutrino energy spectrum as a function of time.   

The Search for Exotic Physics with EXO-200

The Enriched Xenon Observatory (EXO-200) is an experimental program searching for neutrinoless double beta decay ($\beta\beta0\nu$) using an extremely low-background time projection chamber containing ~175 kg of liquid xenon enriched to 80\% $^{136}$Xe. Observation of this lepton-number violating decay would demonstrate that neutrinos are Majorana particles and allow determination of the absolute neutrino mass scale. With over 2 years of data collected since May 2011, EXO-200 previously reported the first observation of two neutrino double beta decay ($\beta\beta2\nu$) in $^{136}$Xe and placed stringent constraints on the $\beta\beta0\nu$ mode of $^{136}$Xe. In addition to searching for $\beta\beta0\nu$, the EXO-200 detector is capable of performing searches for more exotic physics. This talk will present recent results from new analyses of the EXO-200 data, including searches for Majoron emission and other exotic decay modes.   

Search for Sterile antineutrinos in MINOS using $\bar \nu_{\mu}$ disappearance

The MINOS experiment measures the disappearance of $\nu_{\mu}$ and $\bar \nu_{\mu}$ using two detectors separated by 734 km. The magnetized MINOS detectors enable to separate neutrinos and antineutrinos on an event-by-event basis. Besides the precise standard three flavor oscillation, MINOS is also capable of looking for sterile neutrino signal driven by large mass splittings. Between 2009 and 2011, the NuMI beam operated in a $\bar \nu_{\mu}$ enhanced configuration, yielding a unique set of antineutrino data, this allows us to do a direct search for sterile antineutrinos. The $\bar\nu_{\mu}\rightarrow \bar \nu_{s}$ oscillations are studied in a 3+1 sterile antineutrino model with one additional sterile antineutrino state and the mixing parameters $\theta_{24}$ and $\Delta m^{2}_{43}$ are constrained. We present the sensitivity to sterile antineutrino in the antineutrino enhanced mode over a large parameter space of $\Delta m^{2}_{43}$ ($10^{-2}\le \Delta m^{2}_{43}\le 100 \ eV^{2}$) favoured by the LSND and MiniBooNE experiments. By combining our data with the reactor disappearance results we will be able to make a direct comparison with the appearance results of LSND and MiniBooNE.   

Measurement of Mixing Parameters and Sterile Neutrino Search at Daya Bay

The Daya Bay reactor neutrino experiment reported the observation of electron antineutrino disappearance from reactors using six antineutrino detectors (ADs) in early 2012. Two ADs were added later in the summer of 2012, completing the designed configuration. We have measured the mixing parameters $\theta_{13}$ and $|\Delta m^2_{ee}|$ based on data collected with the 6AD + 8AD configurations. A search for a fourth (sterile) neutrino has also been performed for the mass-squared difference between 0.001 and 0.3 eV$^2$. Both the overall rates and the spectral shapes of the detected antineutrino events have been taken into account in the analysis. Results from this analysis will be presented.