Measurement of Lambda and Lambda-bar polarization in muon neutrino charged current interactions in NOMAD

The Lambda and Lambda-bar polarizations in muon neutrino charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda's and 649 Lambda-bar's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the Lambda hyperons we observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: Px(xF < 0) = -0.21 +- 0.04 (stat) +- 0.02 (sys). In the current fragmentation region we find Px(xF > 0) = -0.09 +- 0.06 (stat) +- 0.03(sys). A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +- 0.03 (stat) +- 0.01 (sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. The polarization vector of Lambda-bar hyperons measured for the first time in neutrino interactions is found to be consistent with zero.Comment: 5 pages, a contrubution to DIS2002 Conference, Cracow (April, 29 - May, 4

Sterile Neutrino. A short introduction

This is a pedagogical introduction to the main concepts of the sterile neutrino - a hypothetical particle, coined to resolve some anomalies in neutrino data and retain consistency with observed widths of the $W$ and $Z$ bosons. We briefly review existing anomalies and the oscillation parameters that best describe these data. We discuss in more detail how sterile neutrino can be observed, as well as the consequences of its possible existence. In particular, we pay attention to a possible loss of coherence in a model of neutrino oscillations with sterile neutrinos, where this effect might be of a major importance with respect to the 3$\nu$ model. The current status of searches for a sterile neutrino state is also briefly reviewed.Comment: contribution to VLVnT2018 Conferenc

Measurement of Lambda polarization in muon neutrino charged current interactions in NOMAD

The Lambda polarization in muon neutrino charged current interactions has been measured in the NOMAD experiment. We observe negative polarization along the W - boson direction which is enhanced in the target fragmentation region: Px (xF < 0) = -0.21 +/- 0.04(stat) +/- 0.02(sys). In the current fragmentation region we find: Px (xF > 0) = -0.09 +/- 0.06(stat) +/- 0.03(sys). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +/- 0.03(stat) +/- 0.01(sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments.Comment: a talk given at SPIN2000 (Osaka) symposium, October 16-21 (5 pages

Recent results from Daya Bay experiment

This manuscript is a short summary of my talk given at ICNFP2014 Conference. Here we report on new results of $\sin^22\theta_{13}$ and $\Delta m^2_\text{ee}$ measurements, search for the sterile neutrino within $10^{-3} \text{ eV}^2 <\Delta m^2_{41}<0.1\text{ eV}^2$ domain and precise measurement of the reactor absolute antineutrino flux.Comment: 10 pages, 5 figure

Extended Grimus-Stockinger theorem and inverse square law violation in quantum field theory

We study higher-order corrections to the Grimus-Stockinger theorem dealing with the large-distance asymptotic behavior of the wave-packet modified neutrino propagator within the framework of field-theoretical description of the neutrino oscillation phenomenon. We discuss the possibility that these corrections are responsible for breakdown of the classical inverse-square law (ISL) at the macroscopic distances. In particular the ISL violation can be an explanation of the well-known reactor antineutrino anomaly.Comment: 11 pages, no figures. Some additions are done and references are adde

Intrinsic Polarized Strangeness and Lambda Polarization in Deep-Inelastic Production

We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino collisions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented

Recent results in neutrino physics

This manuscript is a shorthand version of my talk given at Odessa Gamov School on Astronomy, Cosmology and Beyond (22-28 August 2011, Odessa, Ukraine). Within this note we very briefly review the main achievements, new results and open problems in neutrino physics of today.Comment: An invited plenar talk at "The XIth G. Gamow's Odessa Astronomical Summer Conference-School, 22-28 August, 2011, Odessa, Ukraine", 6 pages http://www.astro-soc.odessa.ua