Total Neutrino Research Articles

Global Anisotropy versus Small‐Scale Fluctuations in Neutrino Flux in Core‐Collapse Supernova Explosions

Effects of small-scale fluctuations in the neutrino radiation on core-collapse supernova explosions are examined. Through a parameter study with a fixed radiation field of neutrinos, we find substantial differences between the results of globally anisotropic neutrino radiation and those with fluctuations. As the number of modes of fluctuations increases, the shock positions, entropy distributions, and explosion energies approach those of spherical explosion. We conclude that global anisotropy of the neutrino radiation is the most effective mechanism of increasing the explosion energy when the total neutrino luminosity is given. This supports the previous statement on the explosion mechanism by Shimizu and coworkers.

A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory

As photodisintegration of deuterons mimics the disintegration of deuterons by neutrinos , the accurate measurement of the radioactivity from thorium and uranium decay chains in the heavy water in the Sudbury Neutrino Observatory (SNO) is essential for the determination of the total solar neutrino flux. A radium assay technique of the required sensitivity is described that uses hydrous titanium oxide adsorbent on a filtration membrane together with a β−α delayed coincidence counting system. For a 200 tonne assay the detection limit for 232 Th is a concentration of ∼3×10 −16 g Th/g water and for 238 U of ∼3×10 −16 g U/g water. Results of assays of both the heavy and light water carried out during the first 2 years of data collection of SNO are presented.

High-resolution calculations of merging neutron stars - II. Neutrino emission

The remnant resulting from the merger of two neutron stars produces neutrinos in copious amounts. In this paper we present the neutrino emission results obtained via Newtonian, high-resolution simulations of the coalescence event. These simulations use three-dimensional smoothed particle hydrodynamics together with a nuclear, temperature dependent equation of state and a multi-flavour neutrino leakage scheme. We present the details of our scheme, discuss the neutrino emission results from a neutron star coalescence and compare them to the core-collapse supernova case where neutrino emission has been studied for several decades. The average neutrino energies are similar to those in the supernova case, but contrary to the latter, the luminosities are dominated by electron-type antineutrinos which are produced in the hot, neutron-rich, thick disk of the merger remnant. The cooler parts of this disk contain substantial fractions of heavy nuclei, which, however, do not influence the overall neutrino emission results significantly. Our total neutrino luminosities from the merger event are considerably lower than those found in previous investigations. This has serious consequences for the ability to produce a gamma-ray burst via neutrino annihilation. The neutrinos are emitted preferentially along the initial binary rotation axis, an event seen ``pole-on'' would appear much brighter in neutrinos than a similar event seen ``edge-on''.

Total cross section measurements for ν μ, [formula omitted]μ interactions in 3–30 GeV energy range with IHEP-JINR detector and future plans

The results of total cross sections measurements for neutrino and antineutrino interactions with isoscalar target in the 3–30 GeV energy range have been presented. The data were obtained with IHEP-JINR Neutrino Detector (ND) in the “natural” neutrino beam. Now ND is upgraded for study elastic scattering neutrino on protons for determination the contribution strange quarks to proton spin. It also will search ν μ — ν e oscillations with parameters: Pμe ≈ 6 · 10 −4 and ΔM 2 > 2–3 E ν 2. With upgraded ND is possible to measure quasi-elastic scattering (determination of M A ) and total cross section neutrino and antineutrino on nucleon in 1–5 GeV energy range.

New upper limit on the total neutrino mass from the 2 degree field galaxy redshift survey.

We constrain f(nu) identical with Omega(nu)/Omega(m), the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2 Degree Field Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos, and a cosmological constant. Adding constraints from independent cosmological probes we find f(nu)<0.13 (at 95% confidence) for a prior of 0.1<Omega(m)<0.5, and assuming the scalar spectral index n=1. This translates to an upper limit on the total neutrino mass m(nu,tot)<1.8 eV for "concordance" values of Omega(m) and the Hubble constant.

Influence of collective plasma processes on the theoretical flux of solar neutrinos

Calculations using a standard solar model show that the decrease in proton-proton chain nuclear reaction rates due to collective plasma processes increases the theoretical solar neutrino flux, while the decrease in the opacity of the solar interior associated with the same processes decreases this flux. Taking into account both of these effects decreases the total neutrino flux, easing the solar neutrino problem.

What have we learnt about the Sun from the measurement of the 8B neutrino flux?

Abstract By combining the results of SNO and Super-Kamiokande one can derive—in the absence of sterile neutrinos—the total neutrino flux produced from 8B decay in the Sun. We use this information to check the accuracy of several input parameters of solar model calculations. Opacity and p–p fusion cross section are constrained by the 8B flux measurement to the level of few per cent. The central solar temperature is determined to the one-percent level. We also find an upper limit for the flux on Earth of sterile neutrinos. We discuss the role of nuclear physics uncertainties on these determinations.

The luminosity constraint on solar neutrino fluxes

A specific linear combination of the total solar neutrino fluxes must equal the measured solar photon luminosity if nuclear fusion reactions among light elements are responsible for solar energy generation. This luminosity constraint, previously used in a limited form in testing the no neutrino oscillation hypothesis, is derived in a generality that includes all of the relevant solar neutrino fluxes and which is suitable for analyzing the results of many different solar neutrino experiments. With or without allowing for neutrino oscillations, the generalized luminosity constraint can be used in future analyses of solar neutrino data. Accurate numerical values for the linear coefficients are provided.

Effect of Anisotropic Neutrino Radiation on Supernova Explosion Energy

Since SN 1987A, many observations have indicated that supernova explosions are not spherical. The cause of the asymmetric explosion is still controversial (e.g., asymmetry in the envelope, the convective engine in the central core or in the proto-neutron star). In our previous study, anisotropic neutrino radiation has been proposed as an explanation for this asymmetry. In this paper we carried out a series of systematic multidimensional numerical simulations in order to investigate the effect of anisotropic neutrino radiation itself on the supernova explosion energy. The neutrino luminosity and the degree of anisotropy in neutrino radiation were assumed as input parameters, and the numerical results for various parameters were compared with each other. It was found that only a few percent of anisotropy in the neutrino emission distribution is sufficient to increase the explosion energy by a large factor. The explosion energy calculated so far in many supernova models has tended to be too short to explain the observation. Anisotropy of 10% in neutrino radiation roughly corresponds to an enhancement of 4% in total neutrino luminosity as far as the explosion energy is concerned. The increase in the explosion energy due to anisotropic neutrino radiation can be explained as follows. Anisotropically emitted neutrinos locally heat the supernova matter and revive a stalled shock wave in the direction of enhanced radiation. The expansion of the gas by the shock propagation results in a decrease in the neutrino cooling (emission) rate that rapidly decreases with the matter temperature. It is this suppression of energy loss that contributes largely to the increase in explosion energy. The efficiency of neutrino heating (absorption) itself is almost unchanged between anisotropic and spherical models with available energy fixed for neutrinos. In order for a stalled shock wave to revive, enhancement of the local intensity in the neutrino flux is of great importance, rather than that of the total neutrino luminosity over all the solid angle. It is first pointed out that such local neutrino heating is capable of triggering a supernova explosion. Anisotropic neutrino radiation is considered to be a plausible mechanism for a successful explosion other than the so far suggested convective trigger.

Collective neutrino-pair emission due to Cooper pairing of protons in superconducting neutron stars

The neutrino emission due to formation and breaking of Cooper pairs of protons in superconducting cores of neutron stars is considered with taking into account the electromagnetic coupling of protons to ambient electrons. It is shown that collective response of electrons to the proton quantum transition contributes coherently to the complete interaction with a neutrino field and enhances the neutrino-pair production. Our calculation shows that the contribution of the vector weak current to the ν ν ̄ emissivity of protons is much larger than that calculated by different authors without taking into account the plasma effects. Partial contribution of the pairing protons to the total neutrino radiation from the neutron star core is very sensitive to the critical temperatures for the proton and neutron pairing. We show domains of these parameters where the neutrino radiation, caused by a singlet-state pairing of protons is dominating.

Enhancing mechanisms of neutrino transitions in a medium of nonperiodic constant-density layers and in the Earth

The enhancement of the transitions ${\ensuremath{\nu}}_{\ensuremath{\mu}}({\ensuremath{\nu}}_{e})\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}({\ensuremath{\nu}}_{\ensuremath{\mu};\ensuremath{\tau}}),$ ${\ensuremath{\nu}}_{2}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e},$ ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{s},$ ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s},$ etc. of neutrinos passing through a medium of nonperiodic density distribution, consisting of (i) two layers of different constant densities (e.g., Earth core and mantle), or (ii) three layers of constant density with the first and the third layers having identical densities and widths which differ from those of the second layer (e.g., mantle-core-mantle in the Earth), is studied. We find that, in addition to the known local maxima associated with the MSW effect and the neutrino oscillation length resonance (NOLR), the relevant two-neutrino transition probabilities have new resonance-like absolute maxima. The latter correspond to a new effect of total neutrino conversion and are absolute maxima in any independent variable: the neutrino energy, the layers widths, etc. We find the complete set of such maxima. We prove that the NOLR and the new absolute maxima are caused by a maximal constructive interference between the amplitudes of the neutrino transitions in the different density layers. We show that the strong resonance-like enhancement of the transitions in the Earth of the Earth-core-crossing solar and atmospheric neutrinos is due to the effect of total neutrino conversion.

Cancellations in neutrinoless double beta decay and the neutrino mass matrix

In a degenerate scheme with mass m 0 a complete analysis of the allowed range of the effective electron neutrino Majorana mass 〈m〉 is performed. Special attention is paid to effects of cancellations caused either by intrinsic CP parities of the eigenstates ( CP invariance) or by complex mixing matrix elements ( CP violation). We investigate all possibilities and give in each case constraints on the phases, the relative CP parities or the neutrino mass scale. A solar mixing angle sin 2 2θ smaller than 0.7 jeopardizes the degenerate mass scheme. A key value of 〈m〉/m 0 is identified, which is independent on the solar solution and would rule out certain schemes. Also it would answer the question regarding the presence of CP violation. Even if a total neutrino mass scale and an effective mass is measured, the value of the phases or parities is not fixed, unless in some special cases. The resulting uncertainty in the other mass matrix elements is at least of the same order than the one stemming from nuclear matrix elements calculations.

Chizhov and petcov reply:

We have found in [1] new conditions for a total neutrino conversion in the case of neutrino oscillations taking place in a medium, consisting of n = 2 (or 3) alternating layers with constant densities $N_1$ and $N_2$. It is claimed in [4] that our results are particular case of enhancement of neutrino oscillations, which was suggested earlier by other authors and was widely discussed in the literature. We refute these claims, confirming the novelty of our results.

Comment on "New conditions for a total neutrino conversion in a medium"

We show that the conditions for total neutrino conversion found in [1] are equivalent to the conditions of maximal depth (parametric resonance) and ($\pi/2 + \pi k$) - phase of parametric oscillations. Therefore the effects considered in [1] are a particular case of the parametric resonance in neutrino oscillations. The existence of strong enhancement peaks in transition probability P rather than the condition P=1 is of physical relevance. We comment on possible realizations and implications of the parametric enhancement of neutrino oscillations.

Extracting matter effects, masses and mixings at a neutrino factory

We discuss and quantify different possibilities to determine matter effects, the value and the sign of $Delta m^2_{31}$, as well as the magnitude of $\sin^2 2\theta_{13}$ in very long baseline neutrino oscillation experiments. We study neutrino oscillation at a neutrino factory in the $\nu_\mu\to\nu_\mu$ disappearance and $\nu_e\to\nu_\mu$ appearance channels with and without muon charge identification. One possibility is to analyze the $\nu_e\to\nu_\mu$ appearance channels leading to wrong sign muon events, which requires however very good muon charge identification. Without charge identification it is still possible to operate the neutrino factory both with $\mu^-$ and $\mu^+$ beams and to analyze the differences in the total neutrino event rate spectra. We show that this leads already to a quite good sensitivity, which may be important if right sign charge rejection capabilities are insufficient. With muon charge identification one can study the $\nu_\mu\to\nu_\mu$ disappearance and the $\nu_e\to\nu_\mu$ appearance channels independently. The best method is finally achieved by combining all available information of the $\nu_\mu\to\nu_\mu$ disappearance and $\nu_e\to\nu_\mu$ appearance channels with charge identification and we show the sensitivity which can be achieved.

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.

New Conditions for a Total Neutrino Conversion in a Medium

A new effect of total neutrino conversion is possible when neutrino propagates through multi-layer medium of nonperiodic constant density layers. The effect can take place in the oscillations in the Earth of the Earth-core-crossing solar and atmospheric 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.

New physics potential with a neutrino telescope

Active Galactic Nuclei are considered as sources of neutrinos, with neutrino energies extending up to 10^{18} eV. It is expected that these highly energetic cosmic neutrinos will be detected by the neutrino telescopes, presently under construction. The detection process is very sensitive to the total muon neutrino cross-section. We examine how the total cross section changes at high energies, by the single production of excited fermions (excited muon and muon-neutrino). For parameters (masses, couplings) of the excited fermions allowed by the experimental constraints, we find that for energies of the incoming muon-neutrino above 100 TeV the cross-section for single production of (excited muon and muon-neutrino) supersedes the standard total cross-section.

A Seismic Solar Model Deduced from the Sound-Speed Distribution and an Estimate of the Neutrino Fluxes

Abstract We have deduced the density, pressure, temperature, and hydrogen profiles in the solar interior by solving the basic equations governing the stellar structure with the imposition that the sound-speed profile is that determined by the helioseismic data of Libbrecht et al. (1990; AAA 52.080.103) and Jiménez et al. (1988; AAA 45.080.041). This approach is completely different from that of the standard solar model, and is based on more experimentally well-determined data. We solved the equations by requiring that the mass and mean molecular weight at the surface match the solar mass and a certain fixed value, respectively, as the outer boundary conditions. Together with these conditions and the appropriate inner boundary conditions, these equations were reduced to a boundary-value problem. We examined whether the luminosity at the surface matches the observed value. The error levels were estimated by a Monte-Carlo simulation with Gaussian noise on the sound-speed profile. The thus-constructed seismic model marginally satisfies the luminosity condition, L(R⊙) = L⊙, at the 3σ level. Using this seismic model, we estimated the neutrino fluxes, and found that the 8B neutrino flux is about 60% of that of the standard solar model. This model does not seem to contradict the Kamiokande neutrino detection experiment. The 7Be neutrino flux of the model is about 20% smaller than the standard solar model, and the pp-neutrino flux of the model is almost the same as that of the standard solar model. We estimated the total neutrino capture rate of the chlorine experiment (Homestake) and that of the gallium experiments (GALLEX and SAGE), except for a contribution from the CNO cycle, by scaling the capture rates based on the standard solar model. The thus-estimated capture rates are 5.62 SNU and 117 SNU, respectively, and are higher than those observed at the 3σ error level.