Constraints on Neutrino Lifetime from the Sudbury Neutrino Observatory Benjamin Land on behalf of the SNO Collaboration

Objective Neutrino Lifetime Use solar neutrino data from the SNO detector to place a limit on Since neutrinos have mass, it Survival Probability for Various Lifetimes the lifetime of neutrino mass state two. As solar neutrinos are an is possible that a "heavy" important background for rare event searches, understanding the neutrino might decay into some lighter particle. solar flux is important for future experiments. As a rare event search in its own right, performing this analysis develops skills in The long baseline between the modeling and simulation broadly applicable to the goals of the Earth and the Sun makes a NSSC. nice test beam to search for decay. The SNO Detector In this regime, neutrinos originating in the Sun could SNO was a one kiloton heavy water decay in-flight to the Earth and neutrino detector constructed 6800 not show up in the data. feet underground in Sudbury, Canada. Since the neutrinos are all ultra-relativistic particles, their The primary goal of SNO was to decay times are affected by relativity. perform a precision measurement of the solar neutrino flux. This leads to an energy dependent decay probability between the Sun and the Earth that can be fit for in an analysis. This measurement resolved a previously measured deficit of solar neutrinos by demonstrating neutrino Fit Development mixing, requiring a nonzero neutrino mass, ultimately receiving the 2015 A detailed Monte-Carlo (MC) simulation of the detector is performed to predict how Nobel Prize. signals and backgrounds should look in the detector.

SNO data can still be analyzed to test The detector data may then be compared to the MC probability distributions (PDFs) models and search for new physics! to extract physical parameters, such as the neutrino lifetime. Test Fit Observable Histograms To do this extraction, four Neutrino Detection dimensional PDFs are created Neutrinos interact with the heavy water through the weak nuclear with the dimensions chosen force via a few processes: Elastic Scatter (ES), Charged Current to maximize separation of (CC), or Neutral Current (NC) signal and background events: the angle of the event relative to the sun, the observed energy, the isotropy of the detected light, and the radius of the event within the detector.

To ensure this extraction operates correctly, it is first The energetic electrons from these processes produce Cherenkov performed on fake data radiation which is detected on an array of about 10,000 photo- seeded with a known value multiplier tubes (PMTs). for all parameters. This is done many times, and for each parameter a fractional bias and deviation from truth normalized by uncertainty (pull) is computed. Parameter Biases Parameter Pulls

Solar Neutrinos The sun is powered by nuclear fusion Proton-proton Fusion Chain chains that produce various neutrino spectra.

This fusion takes place deep within the solar core where densities are very high.

These high (electron) densities alter With biases and pulls consistent with zero, and a pull width consistent neutrino propagation in the sun: the with one, this fit is performing well, and should accurately extract the Mikheyev–Smirnov–Wolfenstein neutrino lifetime from SNO data! (MSW) effect. Conclusion / Future Work The MSW effect leads to an energy dependent admixture of neutrino mass With sensitivity to NC and CC interactions, SNO has made precision states. measurements of solar neutrinos, and the data can be used to test models of new physics. This energy dependence is observed as "survival probability" curves in solar neutrino experiments: the probability to detect what was initially an Neutrino decay, if it exists, should impart an energy dependent electron neutrino as some other neutrino flavor. distortion to the survival probability of solar neutrinos. Neutrino Survival Probability Solar Neutrino Energy Spectra A fit has been developed that should provide a competitive neutrino lifetime limit for mass state two by analyzing SNO data. This fit will be run pending SNO collaboration review and a paper published with the final result. There is a possibility of extending this fit to provide a constraint for the HEP neutrinos which have a lower flux but similar energy range as the Boron-8 neutrinos.

Acknowledgments: This material is based upon work supported by the Department of Energy National Nuclear Security Administration through the Nuclear Science and Security Consortium under Award Number(s) DE-NA0003180.