arXiv subjects

P. C. de Holanda

Publications and source records attributed to P. C. de Holanda.

32 records · Page 2Linked to original sources

arXiv2004

Homestake result, sterile neutrinos and low energy solar neutrino experiments

The Homestake result is about ~ 2 σlower than the Ar-production rate, Q_{Ar}, predicted by the LMA MSW solution of the solar neutrino problem. Also there is no apparent upturn of the energy spectrum (R \equiv N_{obs}/N_{SSM}) at low energies in SNO and Super-Kamiokande. Both these facts can be explained if a light, Δm^2_{01} ~ (0.2 - 2) \cdot 10^{-5} eV^2, sterile neutrino exists which mixes very weakly with active neutrinos: \sin^2 2α~ (10^{-5} - 10^{-3}). We perform both the analytical and numerical study of the conversion effects in the system of two active neutrinos with the LMA parameters and one weakly mixed sterile neutrino. The presence of sterile neutrino leads to a dip in the survival probability in the intermediate energy range E = (0.5 - 5) MeV thus suppressing the Be, or/and pep, CNO as well as B electron neutrino fluxes. Apart from diminishing Q_{Ar} it leads to decrease of the Ge-production rate and may lead to decrease of the BOREXINO signal and CC/NC ratio at SNO. Future studies of the solar neutrinos by SNO, SK, BOREXINO and KamLAND as well as by the new low energy experiments will allow us to check this possibility. We present a general analysis of modifications of the LMA energy profile due to mixing with new neutrino states.

hep-ph↗

arXiv2004

Effects of non-standard neutrino interactions on MSW-LMA solution to the solar neutrino problem

We show that the non-standard neutrino interactions can play a role as sub-leading effect on the solar neutrino oscillations. We observe that very small flavor universality violations of order of 0.1-0.2 G_F is sufficient to induce two phenomena: suppression of the eletronic neutrino earth regeneration and a shift of the resonance layer in the sun. We obtain these phenomena even in the absence of any flavor changing interactions. We discuss their consequences and confront with a global analysis of solar+KamLAND results. We conclude that a new compatibility region in the Delta m^2 x tan^2θ, which we call very low Large Mixing Angle region, is found for Delta m^2 ~ 1e-5 eV^2 and tan^2θ= 0.45.

hep-ph↗

arXiv2003

Solar neutrinos: the SNO salt phase results and physics of conversion

We have performed analysis of the solar neutrino data including results from the SNO salt phase as well as the combined analysis of the solar and the KamLAND results. The best fit values of neutrino parameters are Delta m^2 = 7.1e-5 eV^2, tan^2θ= 0.40 with the boron flux f_B = 1.04. New SNO results strongly disfavor maximal mixing and the h-LMA region (Delta m^2 > 1e-4 eV^2) which is accepted now at the 3-sigma level. We find the 3-sigma upper bounds: Delta m^2 < 1.7e-4$ eV^2 and tan^2θ< 0.64, and the lower bound Delta m^2 > 4.8e-5 eV^2. Non-zero 13-mixing does not change these results significantly. The present data determine quantitatively the physical picture of the solar neutrino conversion. At high energies relevant for SNO and Super-Kamiokande the deviation of the effective survival probability from the non-oscillatory value is about 10 - 14%. The oscillation effect contribution to this difference about 10% and the Earth regeneration is about 3 - 4%. At low energies (E < 1 MeV) the matter corrections to vacuum oscillation effect are below 5%. The predictions for the forthcoming measurements are given which include the spectral distortion and CC/NC ratio at SNO, the Day-Night asymmetry, the KamLAND spectrum and rate.

hep-ph↗

arXiv2003

Large mixing angle solution to the solar neutrino problem and random matter density perturbations

There are reasons to believe that mechanisms exist in the solar interior which lead to random density perturbations in the resonant region of the Large Mixing Angle solution to the solar neutrino problem. We find that, in the presence of these density perturbations, the best fit point in the (sin^2(2θ), Delta_m^2) parameter space moves to smaller values, compared with the values obtained for the standard LMA solution. Combining solar data with KamLAND results, we find a new compatibility region, which we call VERY-LOW LMA, where sin^2(2θ) ~ 0.6 and Delta_m^2~2e-5 eV^2, for random density fluctuations of order 5% < ξ< 8%. We argue that such values of density fluctuations are still allowed by helioseismological observations at small scales of order 10 - 1000 km deep inside the solar core.

hep-ph↗

arXiv2003

Status of a hybrid three-neutrino interpretation of neutrino data

We reanalyze the non-standard interaction (NSI) solutions to the solar neutrino problem in the light of the latest solar, atmospheric and reactor neutrino data. We show that such solutions, although preferred by the solar data and consistent with the oscillation description of the atmospheric neutrino data, are ruled out by the first results of the KamLAND reactor experiment, at more than 3_sigma.

hep-ph↗

arXiv2002

LMA MSW solution of the solar neutrino problem and first KamLAND results

The first KamLAND results are in a very good agreement with the predictions made on the basis of the solar neutrino data and the LMA realization of the MSW mechanism. We perform a combined analysis of the KamLAND (rate, spectrum) and the solar neutrino data with a free boron neutrino flux f_B. The best fit values of neutrino parameters are Delta m^2 = 7.3e-5 eV^2, tg^2 theta = 0.41 and f_B = 1.05 with the 1 sigma intervals: Delta m^2 = (6.2 - 8.4)e-5 eV^2, tg^2 theta = 0.33 - 0.54. We find the 3 sigma upper bounds: Delta m^2 < 2.8e-4 eV^2 and tg^2 theta < 0.84, and the lower bound Delta m^2 > 4e-5 eV^2. At 99% C.L. the KamLAND spectral result splits the LMA region into two parts with the preferred one at Delta m^2 < 1e-4 eV^2. The higher Delta m^2 region is accepted at about 2 sigma level. We show that effects of non-zero 13-mixing, sin^2 theta_{13} < 0.04, are small leading to a slight improvement of the fit in higher Delta m^2 region. In the best fit point we predict for SNO: CC/NC = 0.33 +0.05-0.03 and A_{DN}(SNO) = 2.8+-0.8 % (68% C.L.), and A_{DN}(SNO) < 9 % at the 3 sigma level. Further improvements in the determination of the parameters are discussed and implications of the solar neutrino and KamLAND results are considered.

hep-ph↗

arXiv2002

Searches for sterile component with solar neutrinos and KamLAND

Possible mixing of the active and sterile neutrinos has been considered both in the single Delta m^2 approximation and in the case of more than one Delta m^2. We perform global fit of the available solar neutrino data with free boron neutrino flux in the single Delta m^2 context. The best fit value corresponds to zero fraction of sterile component eta=0. We get the upper bounds: eta<0.26 (0.64) at 1σ(3 sigma). Due to degeneracy of parameters no one individual experiment restricts eta. The bound appears as an interplay of the SNO and Gallium as well as SuperKamiokande data. Future measurements of the NC/CC ratio at SNO can strengthen the bound down to eta<0.5 (3 sigma). If KamLAND confirms the LMA solution with its best fit point a combined analysis of the KamLAND and solar neutrino results will lead to eta<0.19 (0.56) at 1 sigma (3 sigma). We find that existence of sterile neutrino can explain the intermediate value of suppression of the KamLAND event rate: R_{KL}~0.75-0.90 in the case when more than one Delta m^2 is involved.

hep-ph↗

arXiv2002

Solar neutrinos: global analysis with day and night spectra from SNO

We perform global analysis of the solar neutrino data including the day and night spectra of events at SNO. In the context of two active neutrino mixing, the best fit of the data is provided by the LMA MSW solution with Delta m^2 = 6.15 10^{-5} eV^2, tan^2θ= 0.41, f_B = 1.05, where f_B is the boron neutrino flux in units of the corresponding flux in the Standard Solar Model (SSM). At 3 sigma level we find the following upper bounds: tan^2θ< 0.84 and Delta m^2 < 3.6 10^{-4} eV^2. From 1 sigma-interval we expect the day-night asymmetries of the charged current and electron scattering events to be: A_{DN}^{CC} = 3.9 +3.6-2.9 and A_{DN}^{ES} = 2.1 +2.1-1.4. The only other solution which appears at 3 sigma-level is the VAC solution with Delta m^2 = 4.5 10^{-10} eV^2, tan^2θ= 2.1 and f_B=0.75. The best fit point in the LOW region, with Delta m^2 = 0.93 10^{-7} eV^2 and tan^2θ= 0.64, is accepted at 99.95% (3.5 sigma) C.L. . The least chi^2 point from the SMA solution region, with Delta m^2 = 4.6 10^{-6} eV^2 and tan^2θ= 5 10^{-4}, could be accepted at 5.5 sigma-level only. In the three neutrino context the influence of theta_{13} is studied. We find that with increase of theta_{13} the LMA best fit point shifts to larger Delta m^2, mixing angle is practically unchanged, and the quality of the fit becomes worse. The fits of LOW and SMA slightly improve. Predictions for KamLAND experiment (total rates, spectrum distortion) have been calculated.

hep-ph↗

arXiv2002

Global Analysis of the post-SNO Solar Neutrino Data for Standard and Non-Standard Oscillation Mechanisms

What can we learn from solar neutrino observations? Is there any solution to the solar neutrino anomaly which is favored by the present experimental panorama? After SNO results, is it possible to affirm that neutrinos have mass? In order to answer such questions we analyze the current available data from the solar neutrino experiments, including the recent SNO result, in view of many acceptable solutions to the solar neutrino problem based on different conversion mechanisms, for the first time, using the same statistical procedure. This allows us to do a direct comparison of the goodness of the fit among different solutions, from which we can discuss and conclude on the current status of each proposed dynamical mechanism. These solutions are based on different assumptions: (a) neutrino mass and mixing, (b) non-vanishing neutrino magnetic moment, (c) the existence of non-standard flavor-changing and non-universal neutrino interactions and (d) the tiny violation of the equivalence principle. We investigate the quality of the fit provided by each one of these solutions not only to the total rate measured by all the solar neutrino experiments but also to the recoil electron energy spectrum measured at different zenith angles by the Super-Kamiokande collaboration. We conclude that several non-standard neutrino flavor conversion mechanisms provide a very good fit to the experimental data which is comparable with (or even slightly better than) the most famous solution to the solar neutrino anomaly based on the neutrino oscillation induced by mass.

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arXiv2000

On the massless "just-so" solution to the solar neutrino problem

We study the effect of the non-resonant, vacuum oscillation-like neutrino flavor conversion induced by non-standard flavor changing and non-universal flavor diagonal neutrino interactions with electrons in the sun. We have found an acceptable fit for the combined analysis for the solar experiments total rates, the Super-Kamiokande (SK) energy spectrum and zenith angle dependence. Phenomenological constraints on non-standard flavor changing and non-universal flavor diagonal neutrino interactions are considered.

hep-ph↗

arXiv2000

Status of the solution to the solar neutrino problem based on non-standard neutrino interactions

We analyze the current status of the solution to the solar neutrino problem based both on: a) non-standard flavor changing neutrino interactions (FCNI) and b) non-universal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the sun as well as in the earth provide a good fit not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration. This solution does not require massive neutrinos and neutrino mixing in vacuum. Stringent experimental constraints on FCNI from bounds on lepton flavor violating decays and on FDNI from limits on lepton universality violation rule out $ν_e \to ν_μ$ transitions induced by New Physics as a solution to the solar neutrino problem. However, a solution involving $ν_e \to ν_τ$ transitions is viable and could be tested independently by the upcoming $B$-factories if flavor violating tau decays would be observed at a rate close to the present upper bounds.

hep-ph↗

arXiv1999

Status of the MSW Solutions to the Solar Neutrino Problem

We present an updated global analysis of two-flavor MSW solutions to the solar neutrino problem in terms of conversions of nu_e into active or sterile neutrinos. We perform a fit to the full data set corresponding to the 825-day Super-Kamiokande data sample as well as to Chlorine, GALLEX and SAGE experiments. We use all measured total event rates as well as Super-Kamiokande data on the zenith angle dependence, energy spectrum and seasonal variation of the events. For conversions into active neutrinos we find that, although the data on the total event rates favours the Small Mixing Angle (SMA) solution, once the full data set is included both SMA and Large Mixing Angle (LMA) solutions give an equivalent fit to the data. The best-fit points for the combined analysis are Delta m^2=3.6 10^{-5} eV^2 sin^2(2theta)=0.79 with chi^2_min=35.4/30 d.o.f and Delta m^2=5.1~ 10^{-6} eV^2 and sin^2(2theta)=5.5 10^{-3} with chi^2_min=37.4/30 d.o.f. In contrast with the earlier 504-day study of Bahcall-Krastev-Smirnov our results indicate that the LMA solution is not only allowed, but slightly preferred. We also show that seasonal effects, although small, may still reach 8.5 % at the best-fit LMA solution without conflict with the hints of a day-night variation (6% is due to the eccentricity of the Earth's orbit). For conversions into sterile neutrinos only the SMA solution is allowed with best-fit point Delta m^2=5.0 10^{-6} eV^2 and sin^2(2theta)=3. 10^{-3} and chi^2_min=40.2/30 d.o.f. We also consider departures of the Standard Solar Model of Bahcall and Pinsonneault 1998 by allowing arbitrary 8^B and hep fluxes. Best fit is obtained for ^8B/^8B_SSM=0.61 (1.37) and hep/hep_SSM=12 (38) for the SMA (LMA) solution.

hep-ph↗

arXiv1999

Seasonal Dependence in the Solar Neutrino Flux

MSW solutions of the solar neutrino problem predict a seasonal dependence of the zenith angle distribution of the event rates, due to the non-zero latitude at the Super-Kamiokande site. We calculate this seasonal dependence and compare it with the expectations in the no-oscillation case as well as just-so scenario, in the light of the latest Super-Kamiokande 708-day data. The seasonal dependence can be sizeable in the large mixing angle MSW solution and would be correlated with the day-night effect. This may be used to discriminate between MSW and just-so scenarios and should be taken into account in refined fits of the data.

hep-ph↗

arXiv1998

Effects of magnetohydrodynamics matter density fluctuations on the solar neutrino resonant spin-flavor precession

Taking into account the stringent limits from helioseismology observations on possible matter density fluctuations described by magnetohydrodynamics theory, we find the corresponding time variations of solar neutrino survival probability due to the resonant spin-flavor precession phenomenon with amplitude of order O(10%). We discuss the physics potential of high statistics real time experiments, like as Superkamiokande, to observe the effects of such magnetohydrodynamics fluctuations on their data. We conclude that these observations could be thought as a test of the resonant spin-flavor precession solution to the solar neutrino anomaly.

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