Electron Neutrino Flux Research Articles

The very low energy solar flux of electron and heavy-flavor neutrinos and antineutrinos

We calculate the thermal flux of low-energy solar neutrinos and antineutrinos of all flavors arising from a variety of neutrino pair processes: Compton production (including plasmon-pole diagrams), neutral current decay of thermally populated nuclear states, plasmon decay, and electron transitions from free to atomic bound states. The resulting flux density per flavor is significant (10 8–10 9/cm 2/sec/MeV) below ∼ 5 keV, and the distributions fill much of the valley between the high-energy edge of the cosmic background neutrino spectrum and the low energy tails of the pp-chain electron neutrino and terrestrial electron antineutrino spectra. Thermal neutrinos carry information on the solar core temperature distribution and on heavy flavor neutrino masses for m ν μ or m ν τ ≳ 1 keV. The detection of these neutrinos is a daunting but interesting challenge.

The asymmetry of solar-neutrino fluxes

With effective heliolatitude Leff(n) for each solar-neutrino run n we separate all available Homestake experimental data for more than two solar cycles (1970–1994) on three zones SOUTH, EQUATORIAL, and NORTH in dependence on the heliolatitude (where detected neutrinos cross the Sun’s surface). For each latitudinal zone, we determine the average solar electron neutrino flux and correlations with effective solar-activity parameters for asymmetrical latitudinal belts. The obtained results indicate that neutrino should have nonzero mass and nonzero magnetic moment.

The sun as a high energy neutrino source

Cosmic ray interactions in the solar atmosphere yield a flux of electron and muon neutrinos with energies greater than 10 GeV. We discuss the influence of neutrino oscillations on the event rates in water-based Čerenkov detectors due to this neutrino flux and comment on the possibility of detecting the sun as a high energy neutrino source.

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) detector is a 1000 tonne heavy water Cerenkov detector under construction near to Sudbury in Canada. The aim of the experiment is to detect neutrinos from the sun and other astrophysical sources. The use of heavy water allows both electron neutrinos and all types of neutrinos to be observed by three complementary reactions. The detector will be sensitive to the electron neutrino flux and energy spectrum shape and to the total neutrino flux irrespective of neutrino type. These measurements will provide information which should clarify the role of neutrino oscillations, neutrino magnetic moments and solar model predictions in explanations of the observed deficit in solar neutrino flux. In the event of a supernova it will be very sensitive to muon and tau neutrinos as well as the electron neutrinos emitted in the initial burst enabling sensitive mass measurements as well as providing details of the physics of stellar collapse.

The sudbury neutrino observatory project

The construction of the Sudbury Neutrino Observatory (SNO) project was completed in April, 1998 and the detector is presently in operation as it is being filled with light and heavy water. The SNO detector is a 1,000 tonne heavy water Cerenkov detector situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario, Canada. [1] The project is a Canadian, US and UK collaboration. Through the use of heavy water SNO will be able to detect a number of neutrino reactions, including one sensitive specifically to electron neutrinos and another one which is sensitive to all neutrino types. With these two reactions the detector will be used to search for solar neutrino flavour change without the requirement of electron neutrino flux normalization by solar model calculations. It will also provide unusual sensitivity for other measurements of solar neutrino properties, atmospheric neutrinos and supernova neutrinos.

Solar neutrino interactions with18Oin the SuperKamiokande water Cerenkov detector

The ratio of ${}^{18}\mathrm{O}$ nuclei to electrons in SuperKamiokande is quite small, about 1:5000. However, this nucleus provides two unpaired neutrons and a low threshold for solar neutrino absorption, resulting in an unusually large cross section. The ${}^{18}\mathrm{O}$ nuclei, together with ${}^{17}\mathrm{O}$ and deuterium, will produce in excess of 460 scattered electrons per year with energies above the initial SuperKamiokande threshold of 6.5 MeV, or about 6.7% of the total solar neutrino signal, for an electron neutrino flux scaled to the current SuperKamiokande counting rate. We explore whether this might complicate efforts to extract the neutrino spectrum from elastic scattering events and whether there might be any prospect of combining ${}^{18}\mathrm{O}$ and elastic scattering events to separate charged- and neutral-current interactions. Under current operating conditions the answers are no, as the Fermi, Gamow-Teller, and forbidden contributions to the ${}^{18}\mathrm{O}$ cross section conspire to produce a nearly isotropic cross section. Thus most of the events are indistinguishable from background. This result is relevant to SuperKamiokande detection of solar antineutrinos, which arise in certain oscillation scenarios.

Pulsar velocity with three-neutrino oscillations in non-adiabatic processes

We have studied the position dependence of neutrino energy on the Kusenko-Segr\`{e} mechanism as an explanation of the proper motion of pulsars. The mechanism is also examined in three-generation mixing of neutrinos and in a non-adiabatic case. The position dependence of neutrino energy requires the higher value of magnetic field such as $B\sim 3\times 10^{15}$ Gauss in order to explain the observed proper motion of pulsars. It is shown that possible non-adiabatic processes decrease the neutrino momentum asymmetry, whereas an excess of electron neutrino flux over other flavor neutrino fluxes increases the neutrino momentum asymmetry. It is also shown that a general treatment with all three neutrinos does not modify the result of the two generation treatment if the standard neutrino mass hierarchy is assumed.

How large is the7Beneutrino flux from the Sun?

On the basis of present solar neutrino observations and relaxing the constraints from solar models it is possible that most (or nearly all) of the flux of electron neutrinos detected comes from electron capture in $^7{Be}$. These solutions arise from neutrino oscillations in which $\nu_e$ $-$ $\nu_\tau$ mixing suppresses high energy $\nu_e$ and $\nu_e - \nu_\mu$ mixing suppresses low energy $\nu_e$ as qualitatively suggested from some SO(10) grand unified models. The importance of future observations is emphasized.

Constraints on energy independent solutions of the solar neutrino problem

We analyze the latest published solar neutrino data assuming an arbitrary neutrino oscillation/conversion mechanism suppresses the electron neutrino flux from the Sun independent of energy. For oscillations/transitions into active (sterile) neutrinos such mechanisms are ruled out at 99.96 (99.9997)% C.L. assuming the standard solar model by Bahcall and Pinnsoneault '95 correctly predicts all solar neutrino fluxes within their estimated uncertainties. Even if one allows for 8B and 7Be solar neutrino fluxes that are vastly different from the ones in contemporary standard solar models these mechanisms are disfavored by the data.

How well do we (and will we) know solar neutrino fluxes and oscillation parameters?

Assuming neutrino oscillations occur, the pp electron neutrino flux is uncertain by at least a factor of two, the ${\rm ^8B}$ flux by a factor of five, and the ${\rm ^7Be}$ flux by a factor of forty-five. Calculations of the expected results of future solar neutrino experiments (SuperKamiokande, SNO, BOREXINO, ICARUS, HELLAZ, and HERON) are used to illustrate the extent to which these experiments will restrict the range of the allowed neutrino mixing parameters. We present an improved formulation of the ``luminosity constraint'' and show that at 95\% confidence limit this constraint establishes the best available limits on the rate of creation of pp neutrinos in the solar interior and provides the best upper limit to the ${\rm ^7Be}$ neutrino flux.

Neutrino mass and oscillation angle phenomena within the asymmetric left-right models

The light and heavy Majorana neutrinos which appear naturally in the SU(2${)}_{\mathit{L}}$\ifmmode\times\else\texttimes\fi{}SU(2${)}_{\mathit{R}}$\ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathit{B}\mathrm{\ensuremath{-}}\mathit{L}}$ model are investigated. The analysis of the electron neutrino flux propagating through magnetic and matter fields is presented. The cross section of the reaction ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{W}}_{\mathit{k}}^{\mathrm{\ensuremath{-}}}$${\mathit{W}}_{\mathit{n}}^{\mathrm{\ensuremath{-}}}$ is calculated and its dependence on the mass of the right-handed neutrino and the oscillation angle is investigated. The process ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{W}}_{\mathit{k}}^{+}$${\mathit{W}}_{\mathit{n}}^{\mathrm{\ensuremath{-}}}$ is also included in our analysis. \textcopyright{} 1995 The American Physical Society.

Neutrino oscillations in noisy media.

We develop the Redfield equation for \ensuremath{\delta}-correlated Gaussian noise and apply it to the case of two neutrino flavor or spin precession in the presence of a noisy matter density or magnetic field, respectively. The criteria under which physical fluctuations can be well approximated by the \ensuremath{\delta}-correlated Gaussian noise for the above cases are examined. Current limits on the possible neutrino magnetic moment and solar magnetic field suggest that a reasonably noisy solar magnetic field would not appreciably affect the solar electron-neutrino flux. However, if the solar electron density has fluctuations of a few percent of the local density and a small enough correlation length, the MSW effect is suppressed for a range of parameters.

Intrinsic neutrino properties (Physics of anomalous phenomena)

There are several anomalies or “deficits” in neutrino physics: the deficit of the electron neutrino flux from the Sun, the deficit of the muon neutrinos in the atmospheric flux, the 17 kev anomaly in beta spectra etc. The anomalies can be considered as the indications on nonzero values of the neutrino masses, mixing and/or magnetic moments. In this connection we will review some new theoretical ideas related to these neutrino properties.

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) detector is a 1000 ton heavy water (D 2O) Cherenkov detector designed to study neutrinos from the sun and other astrophysical sources. The use of heavy water allows both electron neutrinos and all other types of neutrinos to be observed by three complementary reactions. The detector will be sensitive to the electron neutrino flux and energy spectrum shape and to the total neutrino flux irrespective of neutrino type. These measurements will provide information on both vacuum neutrino oscillations and matter-enhanced oscillations, the MSW effect. In the event of a supernova it will be very sensitive to muon and tau neutrinos as well as the electron neutrinos emitted in the initial burst, enabling sensitive mass measurements as well as providing details of the physics of stellar collapse.

Prompt neutrino production in 400 GeV proton-copper interactions

A new beam-dump experiment has been performed at the CERN Super Proton Synchrotron using the CHARM neutrino detector. The instrumentation and the statistics have been significantly improved with respect to earlier experiments. For a neutrino energy above 20 GeV the asymmetry of the prompt muon-neutrino and electron-neutrino fluxes\([(v_\mu + \bar v_\mu ) - (v_e + \bar v_e )]/[(v_\mu + \bar v_\mu ) + (v_e + \bar v_e )]\) is found to be 0.20±0.10 (stat.)±0.05 (syst.), and the asymmetry of prompt antineutrino and neutrino fluxes for muonneutrinos\((v_\mu - \bar v_\mu )/(v_\mu + \bar v_\mu )\) is 0.02±0.16 (stat.)±0.02 (syst.) in agreement with our previous results. For the cross-section times branching ratio for charm production and semileptonic decay we obtain a value of\(\sigma \times BR\left[ {D(\bar D) \to v_e (\bar v_e ) X} \right] = 1.9 \pm 0.2 \pm 0.2\mu b\) per nucleon. We find no evidence forv τ orv x interactions. The\((v_\tau + \bar v_\tau )\) flux is less than 21% of the total prompt neutrino flux. We derive an improved limit on the branching ratio\(\pi ^0 \to v\bar v\) of 6.5×10−6, and as a verification of the universality of the neutral weak coupling we find\(g_{v_e \bar v_e } /g_{v_\mu \bar v_\mu } = 1.05_{ - 0.18}^{ + 0.15} \).

The mass matrix of neutral fermions and application in some SUSY E6-GUT

The fermion mass spectrum remains one of the outstanding problems of grand unification. The authors discuss the mass matrix of neutral fermions, which arises in three SUSY E6-breaking patterns by including the contributions of the five-dimensional superpotential terms. The solar neutrino puzzle is solved in the breakdown through SU3C*SU3L*SU3R. The model is shown to lead naturally to large oscillations of the doublet neutrino into a sterile fermion leading to the possibility of substantial depletion of the solar electron neutrino flux.

Implications of the mikheyev-smirnov-wolfenstein (MSW) mechanism of amplification of neutrino oscillations in matter

Mikheyev and Smirnov have recently proposed a novel and plausible solution of the solar neutrino problem, based on the resonant amplification of the neutrino oscillations in matter. We comment on several aspects of this mechanism. (i) For the values of neutrino masses and mixing angles predicted by the seesaw model of grand unified theories, the MSW effect may take place naturally in the Sun, leading to a considerable reduction of the flux of solar electron neutrinos, with the dominant transition being v e → v τ (rather than v e → v μ ). (ii) Oscillations between the ordinary neutrinos ( v e, v μ , v τ ) can affect primordial nucleosynthesis, but the effect is small (i.e., the abundance of 4He is predicted to change by less than 1.3 × 10 −3). (iii) A comparison of some of the general properties of neutrino oscillations in matter and in vacuum is given.

Solar neutrino oscillations from superstrings

A recently proposed model of neutrino mass based on the heterotic superstring is shown to lead naturally to large oscillations of the SU(2)-doublet neutrino into sterile fermions leading to the possibility of substantial depletion of the solar electron neutrino flux as suggested by Davis' results. The model also leads to a psuedo-Dirac nuetrino with m v = 10–20 eV, without conflict with null searches for neutrinoless double beta decay.

Prompt neutrino production in 400 GeV proton copper interactions

The prompt electron neutrino and muon neutrino fluxes from proton copper interactions at 400 GeV/ c proton momentum have been measured. The asymmetry between the prompt electron (anti) neutrino and the prompt muon (anti) neutrino event rates above 20 GeV is A eμ = (N e − N μ (N c + N μ) = 0.07 ± 0.08 corresponding to an N e/ N μ ratio of 1.14 −0.16 −0.19. The cross section weighted charge asymmetry for electrons and muons combined is A ν ν = 0.15 ± 0.08 . The number of D decays into ν e and ν μ is (4.1 ± 0.9) × 10 −4 per incident proton. No evidence for ν τ interactions was found.

Direct approach to resolve the solar-neutrino problem.

A direct approach to resolve the solar-neutrino problem would be to observe neutrinos by use of both neutral-current and charged-current reactions. Then, the total neutrino flux and the electron neutrino flux would be separately determined to provide independent tests of the neutrino-oscillation hypothesis and the standard solar model. A large heavy-water Cherenkov detector, sensitive to neutrinos from /sup 8/B decay via the neutral-current reaction ..nu..+d..--> nu..+p+n and the charged-current reaction ..nu../sub e/+d..-->..e/sup -/+p+p is suggested for this purpose.