Generation Neutrino Research Articles

K2K and a next generation neutrino oscillation experiment

Results of K2K and a plan of the next generation long baseline neutrino experiment is described. K2K experiment has confirmed neutrino oscillation in Δ m 2 ∼ 3 × 10 −3 eV 2 region by a well controlled accelerator neutrino experiment. As a next step of understanding neutrinos, T2K (Tokai to Kamioka) experiment has been approved. The experiment will use the high intensity neutrino beam from the JPARC(Japan Proton Accelerator Research Complex) 50 GeV proton synchrotron and Super-Kamiokande. An order of magnitude improvement of the sensitivity in the search of ν μ → ν e and a high precision measurement of ν μ disappearance will be the main objectives of the first stage of the experiment. With success in observing ν μ → ν e in the first stage, CP violation in the lepton sector can be investigated with a larger water Cherenkov detector (Hyper-Kamiokande) with upgraded PS in the future.

Thermal leptogenesis with triplet Higgs boson and mass varying neutrinos

We study the thermal leptogenesis in the scenario where the standard model is extended to include one $SU(2)_{L}$ triplet Higgs boson, in addition to three generations of the right-handed neutrinos. And in the model we introduce the coupling between the Quintessence and the right-handed neutrinos, the triplet Higgs boson, so that the light neutrino masses vary during the evolution of the universe. Assuming that the lepton number asymmetry is generated by the decays of the lightest right-handed neutrino $N_{1}$, we find the thermal leptogenesis can be characterized by four model independent parameters. In the case where the contribution of the triplet Higgs to the lepton asymmetry is dominant, we give the relation between the minimal $M_{1}$ and the absolute mass scale $\bar{m}$ of the light neutrinos, by solving the Boltzmann equations numerically. We will also show that with the varying neutrino masses, the reheating temperature can be lowered in comparison with the traditional thermal leptogenesis.

Symmetric Mass Matrix with Two Zeros in SUSY SO(10) GUT, Lepton Flavor Violations and Leptogenesis

We study the symmetric 2-zero texture of the neutrino mass matrix, which is obtained from the symmetric Dirac neutrino mass matrix with 2-zeros and right-handed Majorana neutrino mass matrix with the general form via the see-saw mechanism, for the SUSY SO(10) GUT model including the Pati-Salam symmetry. We show that the only one texture in our model, having degenerate mass spectrum for the 1st and 2nd generation of right-handed Majorana neutrino, can simultaneously explain the current neutrino experimental data, lepton flavor violating processes and baryon asymmetry of the Universe. Within such a framework, the predicted values of the light and heavy Majorana neutrino masses, together with $|U_{e3}|$, $J_{{\rm CP}}$ and $|< M_{ee} >|$, are almost uniquely determined.

MEGA: a low-background radiation detector

The multiple-element gamma assay (MEGA) is a low-background detector designed to support environmental monitoring and national security applications. MEGA also demonstrates technology needed for Majorana, a next generation neutrino mass experiment. It will employ active and passive shielding to reduce backgrounds. It will also exploit multicoincidence signatures to identify specific radioactive isotopes. MEGA is expected to begin testing in late 2003 for eventual installation at the Waste Isolation Pilot Plant, Carlsbad, NM.

GRB 941017: A Case Study of Neutrino Production in Gamma-Ray Bursts

GRB 941017, a gamma-ray burst of exceptional fluence, has recently been shown to have a high-energy component that is not consistent with the standard fireball phenomenology. If this component is the result of photomeson interactions in the burst fireball, it provides new and compelling support for substantial high-energy neutrino fluxes from this and similar sources. In this Letter, we consider what impact this new information has on the neutrino spectra of gamma-ray bursts and discuss how this new evidence impacts the prospects for detection of such events in next generation neutrino telescopes.

Measuring flavor ratios of high-energy astrophysical neutrinos

We discuss the prospects for next generation neutrino telescopes, such as IceCube, to measure the flavor ratios of high-energy astrophysical neutrinos. The expected flavor ratios at the sources are φνe:φνμ:φντ=1:2:0, and neutrino oscillations quickly transform these to 1:1:1. The flavor ratios can be deduced from the relative rates of showers (νe charged current, most ντ charged current, and all flavors neutral current), muon tracks (νμ charged current only), and tau lepton lollipops and double bangs (ντ charged current only). The peak sensitivities for these interactions are at different neutrino energies, but the flavor ratios can be reliably connected by a reasonable measurement of the spectrum shape. Measurement of the astrophysical neutrino flavor ratios tests the assumed production mechanism and also provides a very long baseline test of a number of exotic scenarios, including neutrino decay, CPT violation, and small-δm2 oscillations to sterile neutrinos. © The American Physical Society.

Invisible Higgs boson decay into massive neutrinos of fourth generation

Results from several recent experiments provide inderect evidences in the favor of existence of a 4th generation neutrino. Such a neutrino of mass about 50 GeV is compatible with current physical and astrophysical constraints and well motivated in the framework of superstring phenomenology. If sufficiently stable the existence of such a neutrino leads to the drastic change of Higgs boson physics: for a wide range of Higgs boson masses the dominant mode of Higgs boson decay is invisible and the branching ratios for the most promising modes of Higgs boson search are significantly reduced. The proper strategy of Higgs boson searches in such a framework is discussed. It is shown that in the same framework the absence of a signal in the search for invisible Higgs boson decay at LEP means either that the mass of Higgs is greater than 113.5 GeV or that the mass difference between the Higgs mass and doubled neutrino mass is small.

PRIMORDIAL4He OVERPRODUCTION DUE TO NEUTRINO OSCILLATIONS

The production of 4He during cosmological nucleosynthesis in the presence of active-sterile oscillations, v e ↔ v 5, which is efficient after decoupling of the electron neutrino, is analysed. The oscillation effects on primordial nucleosynthesis, namely neutrino spectrum distortion, depletion of the electron neutrino number density and generation of neutrino-antineutrino asymmetry, are precisely taken into account. The maximal primordial 4He is calculated, in a self-consistent study of the kinetics of the nucleons and the oscillating neutrinos, for the full range of parameters of the discussed oscillation model. The maximal relative increase of 4He, up to 14% for non-resonant oscillations and up to 32% for resonant oscillations is found. Cosmological constraints on oscillation parameters are discussed.

Single- and multi-photon production in ee collisions at $\sqrt{s}$ up to 209 GeV

Events containing only energetic photons are analysed in a sample of \(628 \mathrm{pb}^{-1}\) of data recorded from \(\rm e^+e^-\) collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The \(e^+ e^-\to \nu\bar{\nu}\gamma(\gamma)\) and \(e^+ e^-\to \gamma\gamma(\gamma)\) cross sections are measured and found to be in agreement with the standard model predictions. The number of light neutrino generations is determined to be \(N_\nu = 2.86 \pm 0.09\). Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits are also set on the parameters of models with extra spatial dimensions, with contact interactions and with excited electrons.

IceCube — the next generation neutrino telescope at the South Pole

IceCube is a large neutrino telescope of the next generation to be constructed in the Antarctic Ice Sheet near theSouth Pole. We present the conceptual design and the sensitivity of the IceCube detector to predicted fluxes of neutrinos, both atmospheric and extra-terrestrial. A complete simulation of the detector design has been used to study the detector's capability to search for neutrinos from sources such as active galaxies, and gamma-ray bursts.

Status of a supersymmetric flavor violating solution to the solar neutrino puzzle with three generations

We present a general study of a three neutrino flavour transition model based on the supersymmetric interactions which violate R-parity. These interactions induce flavour violating scattering reactions between solar matter and neutrinos. The model does not contain any vacuum mass or mixing angle for the first generation neutrino. Instead, the effective mixing in the first generation is induced via the new interactions. The model provides a natural interpretation of the atmospheric neutrino anomaly, and is consistent with reactor experiments. We determine all R-parity violating couplings which can contribute to the effective neutrino oscillations, and summarize the present laboratory bounds. Independent of the specific nature of the (supersymmetric) flavour violating model, the experimental data on the solar neutrino rates and the recoil electron energy spectrum are inconsistent with the theoretical predictions. The confidence level of the $\chi^2$-analysis ranges between $\sim 10^{-4}$ and $\sim 10^{-3}$. The incompatibility, is due to the new SNO results, and excludes the present model. We conclude that a non-vanishing vacuum mixing angle for the first generation neutrino is necessary in our model. We expect this also to apply to the solutions based on other flavour violating interactions having constraints of the same order of magnitude.

A water Cherenkov calorimeter for long baseline neutrino oscillation experiments

We propose a water-based large homogeneous calorimeter as the next generation neutrino detector for ν factories and/or conventional ν beams. The Cherenkov light produced in water is sufficient to have good energy resolution, and the pattern recognition is realized by a modular water tank structure. Monte Carlo simulations show that the detector performance is excellent for identifying neutrino CC events while rejecting backgrounds.

The effective Lagrangian for the seesaw model of neutrino mass and leptogenesis

The effective Lagrangian for the seesaw model is derived including effects due to CP-violation. Besides the usual dimension-5 operator responsible for light neutrino masses, a dimension-6 operator is obtained. For three or less heavy neutrino generations, the inclusion of both operators is necessary and sufficient for all independent physical parameters of the high-energy seesaw Lagrangian to appear in the low-energy effective theory, including the CP-odd phases relevant for leptogenesis. The dimension-6 operator implies exotic low-energy couplings for light neutrinos, providing a link between the high-energy physics and low-energy observables.

NUCLEAR DEVICES AND BASIC NEUTRINO-OSCILLATION RESEARCH

An appropriately placed array of new generation neutrino detectors, in conjunction with the use of nuclear devices as a source of intense flux of neutrinos, can serve as a powerful precision probe of neutrino–oscillation parameters. If such detectors are made mobile by placing them on a criss-crossing grid of railway tracks, one may under certain hostile circumstances use them to locate nuclear powered vehicles like submarines, aircraft carriers and any other strong neutrino sources. Since neutrinos cannot be shielded, it may not be possible to escape detection.

Limits on neutrino masses from tritium β decay

The presently lowest limit for the mass of the electron neutrino is mν < 2.2 eV (95 % C.L.) derived from measurements at Mainz up to 1999. The data taken in 2000 are not fully analyzed yet but limits of possible distortions as reported by the Troitsk group can be given. The next generation neutrino mass experiment KATRIN is briefly discussed.

Neutrino generation by high-intensity lasers

This paper proposes a new concept for generating controlled, high-flux pulses of neutrinos. Laser-induced generation of relativistic protons, followed by pion production and decay, provides the neutrino source. By conservative estimate, the source will yield nanosecond-range pulses of muon–neutrinos, with fluxes of ∼1019 νμ s−1 sr−1 and energies of ∼20 MeV or higher. Concept feasibility depends upon further progress in high-intensity lasers; the process assumes a driving laser with pulse energy ∼8 kJ, providing an irradiance of ∼9 × 1022 W cm−2. The study of the KARMEN time anomaly and neutrino oscillations would be the possible applications of the source.

THE NEUTRINOLESS DOUBLE β DECAY AND THE NEUTRINO MASS HIERARCHY

Recently the evidence of the neutrinoless double β (0νββ) decay has been announced. This means that neutrinos are Majorana particles and their mass hierarchy is forced to certain patterns in the diagonal basis of charged lepton mass matrix. We estimate the magnitude of 0νββ decay in the classification of the neutrino mass hierarchy patterns as Type A, m1,2 ≪ m3, Type B, m1 ~ m2 ≫ m3, and Type C, m1 ~ m2 ~ m3, where mi is the ith generation neutrino absolute mass. The data of 0νββ decay experiment suggest that the neutrino mass hierarchy pattern should be Type B or C. Type B predicts a small magnitude of 0νββ decay which is just edge of the allowed region of experimental value in 95% c.l., where Majorana CP phases should be in a certain parameter region. Type C can induce the suitably large amount of 0νββ decay which is consistent with the experimental data, where overall scale of degenerate neutrino mass plays a crucial role, and its large value can induce the large 0νββ decay in any parameter regions of Majorana CP phases.

Ambiguities of theoretical parameters andCPorTviolation in neutrino factories

We study the sensitivity to the CP/T-violation search in the presence of ambiguities of the theoretical parameters. Three generations of neutrinos are considered. The parameters whose ambiguities are considered are the differences of the squared masses, the mixing angles, and the density of matter. We first consider the statistics that are sensitive to the genuine CP-violation effect originating from the imaginary coupling. No ambiguity of the parameters is considered in this part. It is argued that the widely-adopted usual statistics are not necessarily sensitive to the genuine CP-violation effect. Two statistics that are sensitive to the imaginary coupling are proposed. The qualitative difference between these statistics and the usual one are discussed. Next we proceed to the case where the ambiguity of the parameters is present. The sensitivity of the CP-violation search is greatly spoiled when the baseline length is longer than about one thousand kilometers, which turns out to be due to the ambiguity of the matter effect. Thus the CP-violation search by use of CP conjugate channels turns out to require a low energy neutrino and short baseline length. It is also shown that such a loss of sensitivity is avoided by using T-conjugate oscillation channels.

Implications of a solar-system population of massive 4th generation neutrinos for underground searches of monochromatic neutrino-annihilation signals

Abstract It has been recently pointed out that any primary galactic population of Weakly Interacting Massive Particles (WIMP) generates, through collisions with solar matter, a secondary population of “slow” WIMPs trapped in the inner solar system. We show that taking into account this “slow” solar-system population dramatically enhances the possibility to probe the existence of stable massive neutrinos (of a 4th generation) in underground neutrino experiments. Though neutrinos, with mass in the 45–90 GeV range, can only represent a sparse subdominant component of galactic cold dark matter, a combination of enhancement factors makes it possible to discriminate their contribution to WIMP annihilation effects in the Earth. Our work suggests that a reanalysis of existing underground neutrino data should be able to bring extremely tight constraints on the possible existence of a stable massive 4th neutrino.

CP violation in the minimal supersymmetric seesaw model

We study CP violation in the lepton sector of the supersymmetric extension of the Standard Model with three generations of massive singlet neutrinos with Yukawa couplings Y ν to lepton doublets, in a minimal seesaw model for light neutrino masses and mixing. This model contains six physical CP-violating parameters, namely the phase δ observable in oscillations between light neutrino species, two Majorana phases φ 1,2 that affect ββ 0 ν decays, and three independent phases appearing in Y νY ν † , that control the rate of leptogenesis. Renormalization of the soft supersymmetry-breaking parameters induces observable CP violation at low energies, including T-odd asymmetries in polarized μ→ eee and τ→ℓℓℓ decays, as well as lepton electric dipole moments. In the leading-logarithmic approximation in which the massive singlet neutrinos are treated as degenerate, these low-energy observables are sensitive via Y ν †Y ν to just one combination of the leptogenesis and light-neutrino phases. We present numerical results for the T-odd asymmetry in polarized μ→ eee decay, which may be accessible to experiment, but the lepton electric dipole moments are very small in this approximation. To the extent that the massive singlet neutrinos are not degenerate, low-energy observables become sensitive also to two other combinations of leptogenesis and light-neutrino phases, in this minimal supersymmetric seesaw model.