Search results for " Neutrino"
showing 10 items of 727 documents
Rejection Power of A Horizontal Rpc Telescope For Left and Right Coming Cosmic Muons
1993
Abstract The possibility of performing neutrino astronomy by means of a detector above the ground depends critically on the feasibility of a rejection power on the order of 10 11 required to discriminate the enormous background of cosmic downward going muons from the signal of upward going muons produced by neutrinos. In order to check whether and how this rejection is obtainable, we have built in the Physics Department of the University of Bari a horizontal cosmic muon telescope (MINI) instrumented with resistive plate counters. By performing time-of-flight measurements, we have estimated the rejection power of our telescope for left and right coming cosmic muons. The rejection dependence …
Bilinear R-parity violation and small neutrino masses: A self-consistent framework
2000
We study extensions of supersymmetric models without R-parity which include an anomalous U(1)_H horizontal symmetry. Bilinear R-parity violating terms induce a neutrino mass at tree level of approximately $(\theta^2)^\delta$ eV where $\theta\approx 0.22$ is the U(1)_H breaking parameter and $\delta$ is an integer number that depends on the horizontal charges of the leptons. For $\delta=1$ a unique self-consistent model arises in which i) all the superpotential trilinear R-parity violating couplings are forbidden by holomorphy; ii) the tree level neutrino mass falls in the range suggested by the atmospheric neutrino problem; iii) radiative contributions to neutrino masses are strongly suppre…
Performance of long modules of silicon microstrip detectors
1998
This note describes the performance of modules assembled with up to twelve silicon microstrip detectors. These modules were built for the instrumented Silicon Target (STAR) that has been installed in the NOMAD spectrometer. Laboratory and test beam results are compared with model predictions. For a module of nine detectors, test beam results indicate a signal--to--noise ratio of 19, a hit finding efficiency of 99.8\% and a spatial resolution of 6.0 $\mu$m. Laboratory measurements indicate that modules of twelve detectors exhibit a signal--to--noise ratio of the order of 16.
Oscillations of Dirac and Majorana neutrinos in matter and a magnetic field
2008
We study the evolution of massive mixed Dirac and Majorana neutrinos in matter under the influence of a transversal magnetic field. The analysis is based on relativistic quantum mechanics. We solve exactly the evolution equation for relativistic neutrinos, find the neutrino wave functions, and calculate the transition probability for spin-flavor oscillations. We analyze the dependence of the transition probability on the external fields and compare the cases of Dirac and Majorana neutrinos. The evolution of Majorana particles in vacuum is also studied and correction terms to the standard oscillation formula are derived and discussed. As a possible application of our results we discuss the s…
Sterile neutrino signals from supernovae
2007
We investigate the effects of a mixing of active and sterile neutrinos on the ratios of supernova electron neutrino flux ($F_e$) and antineutrino flux ($F_{\bar e}$) to the total flux of the other neutrino and antineutrino flavours ($F_a$). We assume that the heaviest (in the normal hierarchy) Standard Model neutrino $\nu_3$ mixes with a sterile neutrino resulting in a pair of mass eigenstates with a small mass gap. Using the density matrix formalism we solve numerically the the evolution of neutrino states in the envelope of a supernova and determine the flux ratios $F_e/F_a$ and $F_{\bar{e}}/F_a$ as a function of the active-sterile mixing angle and for the experimentally allowed range of …
Minimal models with light sterile neutrinos
2011
We study the constraints imposed by neutrino oscillation experiments on the minimal extensions of the Standard Model (SM) with $n_R$ gauge singlet fermions ("right-handed neutrinos"), that can account for neutrino masses. We consider the most general coupling to SM fields of the new fields, in particular those that break lepton number and we do not assume any a priori hierarchy in the mass parameters. We proceed to analyze these models starting from the lowest level of complexity, defined by the number of extra fermionic degrees of freedom. The simplest choice that has enough free parameters in principle (i.e. two mass differences and two angles) to explain the confirmed solar and atmospher…
Low-scale seesaw models versusNeff
2014
We consider the contribution of the extra sterile states in generic low-scale seesaw models to extra radiation, parametrized by ${N}_{\text{eff}}$. We find that the value of ${N}_{\text{eff}}$ is roughly independent of the seesaw scale within a wide range. We explore the full parameter space in the case of two extra sterile states and find that these models are strongly constrained by cosmological data for any value of the seesaw scale below $\mathcal{O}(100\text{ }\text{ }\mathrm{MeV})$.
The Minimal 3 + 2 Neutrino Model vs. Higgs Decays
2016
Abstract The minimal 3+2 neutrino model is a Type-I seesaw model with two Weyl fermions, singlets under the Standard Model. Apart from light neutrino masses and mixings, this model can be fully described by four additional parameters. In this work, we study the minimal 3+2 neutrino model in scenarios where the singlets have masses at the GeV scale. This can lead to Higgs decays into heavy neutrinos, which could be observable as displaced vertices at the LHC.
Neutrino conversions in hot plasma
1995
We discuss the excitation of sterile neutrinos in the early universe using general quantum kinetic equations, which also incorporate a possible primordial magnetic field $B$. We find a new contribution to the excitation propability, which has its origin in the shrinkage of the spin vector. In the absence of $B$ nucleosynthesis implies the constraint $\mid \Delta m^2\mid\sin^22\theta_0\lsim 1.6\times 10^{-6}~{\rm eV}^2$ which is more restrictive than previous estimates. We also present examples of possible stringent limits for $B\ne 0$.
Sterile neutrino models and nonminimal cosmologies
2012
Cosmological measurements are affected by the energy density of massive neutrinos. We extend here a recent analysis of current cosmological data to nonminimal cosmologies. Several possible scenarios are examined: a constant $w\ensuremath{\ne}\ensuremath{-}1$ dark energy equation of state, a nonflat universe, a time-varying dark energy component and coupled dark matter-dark energy universes or modified gravity scenarios. When considering cosmological data only, ($3+2$) massive neutrino models with $\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{eV}$ sterile species are allowed at 95% confidence level. This scenario has been shown to reconcile reactor, LSND and MiniBooNE positive signals with nu…