arXiv subjects

Joao Pulido

Publications and source records attributed to Joao Pulido.

31 records · Page 2Linked to original sources

arXiv2005

Low Energy Solar Neutrinos and Spin Flavour Precession

The possibility that the Gallium data effectively indicates a time modulation of the solar active neutrino flux in possible connection to solar activity is examined on the light of spin flavour precession to sterile neutrinos as a subdominant process in addition to oscillations. We distinguish two sets of Gallium data, relating them to high and low solar activity. Such modulation affects principally the low energy neutrinos ($pp$ and $^7 Be$) so that the effect, if it exists, will become most clear in the forthcoming Borexino and LENS experiments and will provide evidence for a neutrino magnetic moment. Using a model previously developed, we perform two separate fits in relation to low and high activity periods to all solar neutrino data. These fits include the very recent charged current spectrum from the SNO experiment. We also derive the model predictions for Borexino and LENS experiments.

hep-ph↗

arXiv2004

LMA and sterile neutrinos: a case for resonance spin flavour precession?

Open questions remain after the confirmation of LMA as the dominant solution to the solar neutrino deficit. These are the apparent time modulation of the solar neutrino event rates in the Homestake, Gallium and SuperKamiokande experiments, possibly related to solar magnetic activity, the discrepancy between the event rate in the Homestake experiment and its theoretical prediction and the absence of the electron spectrum upturn in SuperKamiokande at energies below 6-8 MeV. We search for a possible understanding of these questions in the context of resonant spin flavour precession to sterile neutrinos, assuming a class of magnetic field profiles anchored in the upper radiation/lower convection zone. We consider the simplest such model beyond the standard 2$ν$ flavour LMA one, with one single magnetic moment transition between active and sterile state and vanishing vacuum mixing. The preferred mass square difference is $Δm^2_{10}=O(10^{-8}eV^2)$. The Ga rate appears to be the most sensitive of all to solar activity. It is also found that a field profile extending within a longer region in the radial direction is favoured over another with a shorter span, and leads to a stronger suppression than in the LMA case of the intermediate energy neutrinos and some of the $^8 B$ ones.

hep-ph↗

arXiv2003

KamLAND and Solar Antineutrino Spectrum

We use the recent KamLAND observations to predict the solar antineutrino spectrum at some confidence limits. We find that a scaling of the antineutrino probability with respect to the magnetic field profile --in the sense that the same probability function can be reproduced by any profile with a suitable peak field value-- can be utilised to obtain a general shape of the solar antineutrino spectrum. This scaling and the upper bound on the solar antineutrino event rate, that can be derived from the data, lead to: 1) an upper bound on the solar antineutrino flux, 2) the prediction of their energy spectrum, as the normalisation of the spectrum can be obtained from the total number of antineutrino events recorded in the experiment. We get $ϕ_{\barν}<3.8\times 10^{-3}ϕ(^8B)$ or $ϕ_{\barν} <5.5\times 10^{-3}ϕ(^8B)$ at 95% CL, assuming Gaussian or Poissonian statistics, respectively. And for 90% CL these become $ϕ_{\barν}<3.4 \times 10^{-3}ϕ(^8B)$ and $ϕ_{\barν}<4.9\times 10^{-3}ϕ(^8B)$. It shows an improvement by a factor of 3-5 with respect to existing bounds. These limits are quite general and independent of the detailed structure of the magnetic field in the solar interior.

hep-ph↗

arXiv2003

KamLAND, solar antineutrinos and the solar magnetic field

In this work the possibility of detecting solar electron antineutrinos produced by a solar core magnetic field from the KamLAND recent observations is investigated. We find a scaling of the antineutrino probability with respect to the magnetic field profile in the sense that the same probability function can be reproduced by any profile with a suitable peak field value. In this way the solar electron antineutrino spectrum can be unambiguosly predicted. We use this scaling and the negative results indicated by the KamLAND experiment to obtain upper bounds on the solar electron antineutrino flux. We get $ϕ_{\barν}<3.8\times 10^{-3}ϕ(^8B)$ at 95% CL. For 90% CL this becomes $ϕ_{\barν}<3.4\times 10^{-3}ϕ(^8B)$, an improvement by a factor of 3-5 with respect to existing bounds. These limits are independent of the detailed structure of the magnetic field in the solar interior. We also derive upper bounds on the peak field value which are uniquely determined for a fixed solar field profile. In the most efficient antineutrino producing case, we get (95% CL) an upper limit on the product of the neutrino magnetic moment by the solar field $μB< 2.8\times 10^{-19}$ MeV or $B_0 \leq 4.9 \times 10^7 G$ for $μ_ν=10^{-12}μ_B$.

hep-ph↗

arXiv2002

Resonance Spin Flavour Precession of Solar Neutrinos After SNO NC Data

We present an analysis of the solar neutrino data assuming the deficit of solar neutrinos to be originated from the interaction of their transition magnetic moments with the solar magnetic field. We perform fits to the rates only and global fits and consider separately the existing data prior to the announcement of the SNO NC results, and present data. Predictions for the Borexino experiment are also derived. The solar field profiles are taken both in the radiation zone and core of the sun, and in the convective zone. The latter are chosen so as to exhibit a rapid increase across the bottom of the convective zone and a moderate decrease towards the surface. Regarding the field profiles in the radiative zone and core, it is found that the data show a preference for those cases in which a strong field rests at the solar centre with a steep decrease thereafter. For these, the quality of the global fits is as good as the one from the best oscillation solutions and the same as for the convective zone profiles examined. It is also found that the $χ^2$ of the fits increases when the most recent data are considered, owing to the smaller errors involved. This in turn provides more precise predictions for Borexino than previous ones, thus resulting in a clearer possible distinction between magnetic moment and the currently favoured oscillation solutions.

hep-ph↗

arXiv2002

Solar Neutrinos with Magnetic Moment: Rates and Global Analysis

A statistical analysis of the solar neutrino data is presented assuming the solar neutrino deficit to be resolved by the resonant interaction of the neutrino magnetic moment with the solar magnetic field. Four field profiles are investigated, all exhibiting a rapid increase across the bottom of the convective zone, one of them closely following the requirements from recent solar physics investigations. First a 'rates only' analysis is performed whose best fits appear to be remarkably better than all fits from oscillations. A global analysis then follows with the corresponding best fits of a comparable quality to the LMA one. Despite the fact that the resonant spin flavour precession does not predict any day/night effect, the separate SuperKamiokande day and night data are included in the analysis in order to allow for a direct comparison with oscillation scenarios. Remarkably enough, the best fit for rates and global analysis which is compatible with most astrophysical bounds on the neutrino magnetic moment is obtained from the profile which most closely follows solar physics requirements. Allowing for a peak field value of $3\times10^5G$, it is found in this case that $Δm^2_{21}=1.45\times10^{-8}eV^2$, $μ_ν=3.2\times10^{-12}μ_{B}$ (65%CL). The new forthcoming experiments on solar neutrino physics (Kamland and Borexino) will be essential to ascertain whether this fact is incidental or essential.

hep-ph↗

arXiv2001

Global Analysis of Solar Neutrinos with Magnetic Moment and Solar Field Profiles

A global statistical analysis of the pre-SNO solar neutrino data including the rates and recoil electron spectrum in SuperKamiokande is made assuming the solar neutrino deficit to be resolved by the interaction of the neutrino magnetic moment with the solar magnetic field. Given the general characteristics of the field profiles known to lead to the best event rate predictions, several specific choices of profiles are assumed and global fits investigated. Whereas previous studies revealed an excellent quality of the rate fits within the magnetic moment solution to the solar neutrino problem, the global fits are found to be only of reasonable quality and comparable to the global oscillation fits. This is related to the difficulty of any theoretical model to provide at present an adjustable prediction to the spectral data.

hep-ph↗

arXiv2001

Solar neutrinos with magnetic moment and solar field profiles

A statistical analysis of the pre-SNO solar neutrino data is made assuming the solar neutrino deficit to be resolved by the interaction of the neutrino magnetic moment with the solar magnetic field. Given the general characteristics of the field profiles known to lead to the best event rate predictions, several specific choices of profiles are assumed and fits to the rates, to the electron recoil spectrum in SuperKamiokande and to the combined rates and spectrum are performed. Both the rate and spectrum fits are remarkably better than in a previous analysis of the magnetic moment solution which used a former standard solar model and previous data, and in particular, rate fits are far better than those from oscillations. The global analysis also reflects the general very good quality of the fits.

hep-ph↗

arXiv2000

Neutrino Magnetic Moment Solution for the Solar Neutrino Problem and the SNO Experiment

The motivations for the magnetic moment solution to the solar neutrino problem are briefly reviewed and the expected values for a number of observables to be measured by the SNO experiment are calculated assuming three different solar magnetic field profiles. The observables examined are the charged current event rate, the ratio of the neutral current to the charged current event rates and the charged current electron spectrum as well as their first and second moments. The dependence of results on the hep neutrino flux is also analysed and a comparison is made with the corresponding oscillation results.

hep-ph↗

arXiv1998

Solar Magnetic Field Profiles and SuperKamiokande Data

The distortion of the energy spectrum of recoil electrons in SuperKamiokande resulting from several solar magnetic field profiles that are consistent with data and standard solar models is investigated. The aim is to provide a test of the general common features of these field profiles derived in a previous work on the basis of the resonant spin flip flavour mechanism. It is found that the distortion may be visible in the data, becoming possibly clearer when the energy threshold succeeds in being reduced and distinct from the ones resulting from oscillations.

hep-ph↗

arXiv1998

Energy Dependence of Solar Neutrino Suppression and Bounds on the Neutrino Magnetic Moment

An analysis of neutrino electron scattering as applied to the SuperKamiokande solar neutrino experiment with the data from the Homestake experiment leads to an upper bound on the neutrino magnetic moment in the range $μ_{ν_e}\leq(2.9-3.7)\times 10^{-10}μ_{B}$. This range is determined by the spread in the flux predictions from six different standard solar models. We assume equal magnetic moments for all neutrino flavours. This limit is obtained when neutrinos do not undergo any "disappearance" mechanism other than the magnetic moment conversion due to the solar magnetic field and for a total or nearly total suppression of the intermediate energy neutrinos. We also point out that the limit may be further reduced if the threshold energy of the SuperKamiokande detector is decreased.

hep-ph↗

arXiv1998

Possible Tomography of the Sun's Magnetic Field with Solar Neutrinos

The data from solar neutrino experiments together with standard solar model predictions are used in order to derive the possible profile of the magnetic field inside the Sun, assuming the existence of a sizeable neutrino magnetic moment and the resonant spin flavour mechanism. The procedure is based on the relationship between resonance location and the energy dependent neutrino suppression, so that a large neutrino suppression at a given energy is taken to be connected to a large magnetic field in a given region of the Sun. In this way it is found that the solar field must undergo a very sharp increase by a factor of at least 6 - 7 over a distance no longer than 7 - 10% of the solar radius, decreasing gradually towards the surface. The range in which this sharp increase occurs is likely to be the bottom of the convective zone. There are also indications in favour of the downward slope being stronger at the start and more moderate on approaching the solar surface. Typical ranges for the magnetic moment are from a few times 10^{-13}μ_B to its laboratory upper bounds while the mass square difference between neutrino flavours is of order (0.6-1.9) x 10^{-8}eV^2.

astro-ph↗

arXiv1997

Neutrino Magnetic Moment Upper Bound From Solar Neutrino Observations

Using the data from SuperKamiokande, Kamiokande and Homestake solar neutrino experiments we derive an upper bound on the magnetic moment of the neutrino and find $μ_{ν_e}\leq(2.2-2.3)\times 10^{-10}μ_{B}$, within four different standard solar models. We assume equal magnetic moments for all neutrino flavours. This limit is obtained when neutrinos do not undergo any "disappearence" mechanism other than the magnetic moment conversion due to the solar magnetic field and for a total or nearly total suppression of the intermediate energy neutrinos. In our work we consider an energy dependent suppression of solar neutrinos. We also point out that the limit may be further reduced if the detector threshold energy in $ν_{e,x}e^{-}$ scattering with solar neutrinos is decreased.

hep-ph↗