Neutrino–nucleon cross section at intermediate energy from KM3 neutrino telescopes

The capability of a KM³ neutrino telescope to bounds the neutrino–nucleon cross section in the intermediate energy range (10⁵ GeV<E<10⁷ GeV) is studied. We use an observable which only makes use of the upward-going neutrino flux, so that the Earth filters the atmospheric muons, and it is only weakly dependent on the initial astrophysical flux uncertainties and experimental systematic. In order to study the sensitivity to departures from the standard model we have considered a cross section which is a version perturbed of the standard model one, dependent of two parameters. We present the results as regions for the allowed values for both, the parameters space and the cross section.     

Seasonal and energy dependence of solar neutrino vacuum oscillations

We make a global vacuum neutrino oscillation analysis of solar neutrino data, including the seasonal and energy dependence of the recent Super-Kamiokande 708-day results. The best fit parameters for ν_e oscillations to an active neutrino are δm²=4.42×10⁻¹⁰ eV², sin²2θ=0.93. The allowed mixing angle region is consistent with bi-maximal mixing of three neutrinos. Oscillations to a sterile neutrino are disfavored. Allowing an enhanced hep neutrino flux does not significantly alter the oscillation parameters.     

Solar neutrino oscillations in the quasi-vacuum regime

Motivated by recent experimental data, we study solar neutrino oscillations in the range δm²/E ε [10⁻¹⁰, 10⁻⁷] eV²/MeV. In this range vacuum oscillations become increasingly affected by (solar and terrestrial) matter effects for increasing δm², smoothly reaching the MSW regime. A numerical study of matter effects in such “quasi-vacuum” regime is performed. The results are applied to the analysis of the recent solar neutrino phenomenology.     

Limits on the neutrino magnetic moment from solar neutrino experiments

If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μ_νe ≤ (2.2 − 2.3) × 10⁻¹⁰μ_B, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the ν_e,χe⁻ scattering is decreased.     

Interpretation of the recent Kolar events

We give plausible interpretations of the unusual events seen in the proton decay detector at Kolar Gold Fields indicating the existence of a massive (≳2GeV) long lived (10⁻⁸−10⁻⁹s) particle. We show that it is possible to accommodate the particle in the standard model as a fourth generation neutrino, or inE ₆ grand unified theory as a neutral fermion occurring in27 representation or in supersymmetric theory as a scalar neutrino. However, there is a difficulty in explaining the large production rate for the particle.     

Neutrino Oscillations: Entanglement,Energy-Momentum Conservation and QFT

We consider several subtle aspects of the theory of neutrino oscillations which have been under discussion recently. We show that the S-matrix formalism of quantum field theory can adequately describe neutrino oscillations if correct physics conditions are imposed. This includes space-time localization of the neutrino production and detection processes. Space-time diagrams are introduced, which characterize this localization and illustrate the coherence issues of neutrino oscillations. We discuss two approaches to calculations of the transition amplitudes, which allow different physics interpretations: (i) using configuration-space wave packets for the involved particles, which leads to approximate conservation laws for their mean energies and momenta; (ii) calculating first a plane-wave amplitude of the process, which exhibits exact energy-momentum conservation, and then convoluting it with the momentum-space wave packets of the involved particles. We show that these two approaches are equivalent. Kinematic entanglement (which is invoked to ensure exact energy-momentum conservation in neutrino oscillations) and subsequent disentanglement of the neutrinos and recoiling states are in fact irrelevant when the wave packets are considered. We demonstrate that the contribution of the recoil particle to the oscillation phase is negligible provided that the coherence conditions for neutrino production and detection are satisfied. Unlike in the previous situation, the phases of both neutrinos from Z ⁰ decay are important, leading to a realization of the Einstein-Podolsky-Rosen paradox.     

Future atmospheric neutrino data from Super-Kamiokande

Expected sensitivity of future atmospheric neutrino data from Super-Kamiokande on neutrino oscillation physics is discussed. We expect that the accuracy of the sin ²θ₂₃ measurement will be improved with (exposure time) . By analyzing high energy fully contained events, it could be possible to statistically demonstrate the existence of charged current ν_τ interactions at the 3 standard deviation level with a few more years of data. Subdominant ν_μ → ν_e oscillations could be observed if θ₁₃ is near the present limit. However, significantly more data will be required to observe a 3 standard deviation effect.     

Exceptional sensitivity to neutrino parameters with a two-baseline Beta-beam set-up

We examine the reach of a Beta-beam experiment with two detectors at carefully chosen baselines for exploring neutrino mass parameters. Locating the source at CERN, the two detectors and baselines are: (a) a 50 kton iron calorimeter (ICAL) at a baseline of around 7150 km which is roughly the magic baseline, e.g., ICAL@INO, and (b) a 50 kton Totally Active Scintillator Detector at a distance of 730 km, e.g., at Gran Sasso. We choose ⁸B and ⁸Li source ions with a boost factor γ of 650 for the magic baseline while for the closer detector we consider ¹⁸Ne and ⁶He ions with a range of Lorentz boosts. We find that the locations of the two detectors complement each other leading to an exceptional high sensitivity. With γ=650 for ⁸B/⁸Li and γ=575 for ¹⁸Ne/⁶He and total luminosity corresponding to 5×(1.1×10¹⁸) and 5×(2.9×10¹⁸) useful ion decays in neutrino and antineutrino modes respectively, we find that the two-detector set-up can probe maximal CP violation and establish the neutrino mass ordering if sin²2θ₁₃ is 1.4×10⁻⁴ and 2.7×10⁻⁴, respectively, or more. The sensitivity reach for sin²2θ₁₃ itself is 5.5×10⁻⁴. With a factor of 10 higher luminosity, the corresponding sin²2θ₁₃ reach of this set-up would be 1.8×10⁻⁵, 4.6×10⁻⁵ and 5.3×10⁻⁵ respectively for the above three performance indicators. CP violation can be discovered for 64% of the possible δ_CP values for sin²2θ₁₃10⁻³ (8×10⁻⁵), for the standard luminosity (10 times enhanced luminosity). Comparable physics performance can be achieved in a set-up where data from CERN to INO@ICAL is combined with that from CERN to the Boulby mine in United Kingdom, a baseline of 1050 km.     

New Exact Ground States for One-Dimensional Quantum Many-Body Systems

We consider one-dimensional quantum many-body systems with pair interactions in external fields and (re)investigate the conditions under which exact ground-state wave functions of product type can be found. Contrary to a claim in the literature that an exhaustive list of such systems is already known, we show that this list can still be enlarged considerably. In particular, we are able to calculate exact ground-state wave functions for a class of quantum many-body systems with Ax ^–2+Bx ² interaction potentials and external potentials given by sixth-order polynomials.     

Heavy sterile neutrinos and supernova explosions

We consider sterile neutrinos with rest masses 0.2 GeV and with vacuum flavor mixing angles θ²>10⁻⁸ for mixing with τ-neutrinos, or 10⁻⁸<θ²<10⁻⁷ for mixing with muon neutrinos. Such sterile neutrinos could augment core collapse supernova shock energies by enhancing energy transport from the core to the vicinity of the shock front. The decay of these neutrinos could produce a flux of very energetic active neutrinos, detectable by future neutrino observations from galactic supernova. The relevant range of sterile neutrino masses and mixing angles can be probed in future laboratory experiments.     

The Palo Verde reactor neutrino experiment a test for long baseline neutrino oscillations

Our collaboration has installed a long baseline neutrino oscillation experiment at the Palo Verde Nuclear Generating Station in Arizona. 12 tons of Gd loaded liquid scintillator, in a segmented detector, are used to search for oscillations at 740 m distance to three reactors. The anti-neutrino capture on the proton serves as detection reaction. The experiment is expected to reach a sensitivity of Δm² > 1.3 · 10⁻³ eV² and sin²2Θ > 0.1. Our range of sensitivity is tuned to test the ν_μ ↔ ν_e solution of the atmospheric neutrino anomaly.     

Inverse beta decay of arbitrarily polarized neutrons in a magnetic field

We calculate the cross-section of the inverse beta decay process,v _e+n → p+e, in a background magnetic field which is much smaller than m _p ^2/e . Using exact solutions of the Dirac equation in a constant magnetic field, we find the cross-section for arbitrary polarization of the initial neutrons. The cross-section depends on the direction of the incident neutrino even when the initial neutron is assumed to be at rest and has no net polarization. Possible implications of the result are discussed.     

Restrictions on the neutrino magnetic dipole moment

We examine mechanisms for producing neutrino magnetic moments from a wide class of particle theories which are extensions of the standard model. We show that it is difficult to naturally obtain a moment greater than ∼ 10⁻² electron Bohr magnetons. Thus models of phenomena requiring moments of order ∼ 10⁻¹⁰ magnetons, such as those proposed as a resolution to the solar neutrino puzzle, are in conflict with current perceptions in particle physics.     

Solar neutrino oscillation phenomenology

This article summarises the status of the solar neutrino oscillation phenomenology at the end of 2002 in the light of the SNO and KamLAND results. We first present the allowed areas obtained from global solar analysis and demonstrate the preference of the solar data towards the large-mixing-angle (LMA) MSW solution. A clear confirmation in favour of the LMA solution comes from the KamLAND reactor neutrino data. The KamLAND spectral data in conjunction with the global solar data further narrows down the allowed LMA region and splits it into two allowed zones a low Δm ² region (low-LMA) and high Δm ² region (high-LMA). We demonstrate through a projected analysis that with an exposure of 3 kton-year (kTy) KamLAND can remove this ambiguity.     

Update on the search for μ→ e oscillations by the 2 experiment

The neutrino experiment sets the most stringent exclusion limits for _μ→ _e oscillations. Analyzing the data set recorded from Feb.1997 up to March 2000 with the upgraded experimental configuration, the search of _e appearance via the p( _e, e⁺)n reaction yields no hints for neutrino oscillations. Applying a likelihood method to the measured event sample of 11 events (background expectation 12.3 events), we deduce an upper limit of sin² (2Θ) < 1.3 · 10⁻³ for large Δm² > 100 eV² and Δm² < 0.049 eV² for sin² (2Θ)=1.     

Preliminary results and status of the MUNU experiment

We built a low background detector to measure the _ee⁻ elastic cross section at low energy. The detector has been installed close to a nuclear reactor in Bugey and it is running since almost one year. After having reduced the electron background by more than 2 orders of magnitude we are now taking data to be sensitive to a neutrino magnetic moment in the region below 10⁻¹⁰ Bohr magnetons.     

Non-standard interactions using the OPERA experiment

We investigate the implications of non-standard interactions on neutrino oscillations in the OPERA experiment. In particular, we study the non-standard interaction parameter ε _{μ τ} . We show that the OPERA experiment has a unique opportunity to reduce the allowed region for this parameter compared with other experiments such as the MINOS experiment, mostly due to the higher neutrino energies in the CNGS beam compared to the NuMI beam. We find that OPERA is mainly sensitive to a combination of standard and non-standard parameters and that a resulting anti-resonance effect could suppress the expected number of events. Furthermore, we show that running OPERA for five years each with neutrinos and anti-neutrinos would help in resolving the degeneracy between the standard parameters and ε _{μ τ} . This scenario is significantly better than the scenario with a simple doubling of the statistics by running with neutrinos for ten years.     

KARMEN: Neutrino oscillation limits and new results with the upgrade

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS which provides ν_μ's, ν_e's and from the π⁺−μ⁺-decay at rest. The oscillation channels ν_{μ → νe} and are investigated with a 56 t liquid scintillation calorimeter. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin²(2Θ) < 8.5 · 10⁻³ ( ) and sin²(2Θ) < 4.0 · 10⁻² (ν_μ → ν_e) for Δm² > 100 eV². In 1996, the experiment has been upgraded by an additional veto counting system with a total coverage of 300 m². The new system allows the identification of cosmic muons in the vicinity of the detector. Vetoing these muons suppresses energetic neutrons from deep inelastic scattering of muons as well as from μ-capture by a factor of 40. Up to 1996, these neutrons represented the main background for oscillation search. The experimental sensitivity for will be significantly enhanced towards sin²(2Θ) 1.0 · 10⁻³ after a further measuring period of 2–3 years.     

Radiative decays of charged leptons in arbitrary order

In radiative decays of charged leptons induced by non-degenerate neutrino masses and consequent lepton flavour-mixing, the dominant suppression factor at the 1-loop level is (Σ m _a ² )/m _W ² ,m _a being the mass of theath neutrino. We show that this suppression factor is presentin all orders in a class of models including the standard model.     

Radiative neutrino decays in very strong magnetic fields

The radiative decay ν_H → ν_L + γ of massive neutrinos is analyzed in the framework of the standard model with lepton mixing for very strong magnetic fields B B_cr = m²_e/e 4.14 × 10¹³ G. The analysis is based on the approximate decay amplitude obtained by Gvozdev et al. Numerical results as well as analytical approximations for the decay rate are obtained for energies of the initial neutrino below and above the electron-positron pair creation threshold 2m_e.