7Be Neutrinos Research Articles

Re-examination of constraints on the Maxwell-Boltzmann distribution by Helioseismology

Nuclear reactions in stars occur between nuclei in the high-energy tail of the energy distribution and are sensitive to possible deviations from the standard equilibrium thermal-energy distribution, the well-known Maxwell-Boltzmann Distribution (MBD). Strong constraints on such deviations were made previously with the detailed helioseismic information of the solar structure. With a small deviation parameterized with a factor exp[−δ(E/kT)2], it was shown δ restricted between −0.005 and +0.002. These constraints have been carefully re-examined in the present work. We find that a normalization factor was missed in the previous modified MBD. In this work, the normalization factor c is calculated as a function of δ. It shows the factor c is almost unity within the range 0<δ≤0.002, which supports the previous conclusion. However, it demonstrates that δ cannot take a negative value from the normalization point of view. As a result, a stronger constraint on δ is defined as 0≤ δ ≤0.002. The astrophysical implication on the solar neutrino fluxes is simply discussed based on a positive δ value of 0.003. The reduction of the 7Be and 8B neutrino fluxes expected from the modified MBD can possibly shed alternative light on the solar neutrino problem. In addition, the resonant reaction rates for the 14N(p, γ)15O reaction are calculated with a standard MBD and a modified MBD, respectively. It shows that the rates are quite sensitive even to a very small δ. This work demonstrates the importance and necessity of experimental verification or testing of the well-known MBD at high temperatures.

Planetary influence on the young Sun's evolution: the solar neutrino probe

Recent observations of solar twin stars with planetary systems like the Sun, have uncovered that these present a peculiar surface chemical composition. This is believed to be related to the formation of earth-like planets. This suggests that twin stars have a radiative interior that is richer in heavy elements than their envelopes. Moreover, the current standard solar model does not fully agree with the helioseismology data and solar neutrino flux measurements. In this work, we find that this agreement can improve if the Sun has mass loss during the pre-main sequence, as was previously shown by other groups. Despite this better agreement, the internal composition of the Sun is still uncertain, especially for elements heavier than helium. With the goal of inferring the chemical abundance of the solar interior, we tested several chemical compositions. We found that heavy element abundances influence the sound speed and solar neutrinos equally. Nevertheless, the carbon-nitrogen-oxygen (CNO;13N, 15O and 17F) neutrino fluxes are the most affected; this is due to the fact that contrarily to proton-proton (pp, pep, 8B and 7Be) neutrino fluxes, the CNO neutrino fluxes are less dependent on the total luminosity of the star. Furthermore, if the central solar metallicity increases by 30%, as hinted by the solar twin stars observations, this new solar model predicts that 13N, 15O and 17F neutrino fluxes increase by 25%-80% relative to the standard solar model. Finally, we highlight that the next generation of solar neutrino experiments will not only put constraints on the abundances of carbon, oxygen and nitrogen, but will also give some information about their radial distribution.

Probing the Sun’s inner core using solar neutrinos: A new diagnostic method

The electronic density in the Sun's inner core is inferred from the 8B, 7Be and pep neutrino flux measurements of the Super-Kamiokande, SNO and Borexino experiments. We have developed a new method in which we use the KamLAND detector determinations of the neutrino fundamental oscillation parameters: the mass difference and the vacuum oscillation angle. Our results suggest that the solar electronic density in the Sun's inner core (for a radius smaller than 10% of the solar radius) is well above the current prediction of the standard solar model, and by as much as 25%. A potential confirmation of these preliminary findings can be achieved when neutrino detectors are able to reduce the error of the electron-neutrino survival probability by a factor of 15.

Solar neutrino results from Borexino

Borexino is a large-volume liquid scintillator experiment for low energy neutrino detection, operating since May 2007, and installed at the National Laboratory of Gran Sasso. Borexino is the first experiment able to observe in real-time Solar neutrino interactions also in the sub-MeV range. We report with this work the main results achieved in the Solar neutrino sector by Borexino. In particular, we report the results on the measured interaction rates of 7Be, 8B, and pep neutrinos, and their impacts on the physics of neutrino oscillations.

About a possibility of measuring the central temperature of the Sun through the regeneration of the 7Be neutrinos in the Earth

The solar neutrino's 7Be line (Eν = 0.862 MeV) has a width of order the temperature in the center of the Sun (∼ 1 keV).The regeneration of neutrinos from remote structures of the Earth is suppressed due to the averaging of the effect over the width of the 7Be line (oscillation dying effect). We discuss a possibility of measuring the width of the beryllium line at large liquid scintillator detector (LENA) by measuring the electron neutrino flux at different nadir angles of neutrino trajectories.

Precision measurement of the 7Be solar neutrino flux and its day-night asymmetry with Borexino

Borexino measures the 7Be solar neutrino flux on 740 live days of data-taking to be 46±1.5+1.6−1.5 events/(day · 100 tons) which corresponds to an equivalent unoscillated flux on Earth of (3.11±0.10+0.11−0.10)·109sec −1 cm−2. This result excludes the no-oscillation hypothesis at 5 σ and provides a precise measurement of the survival probability Pee in the vacuum dominated oscillation regime Pee = 0.51±0.07. Borexino also measures the day-night asymmetry of the 7Be neutrino rate with a total error of 1.4% and finds it to be consistent with zero. This result is in agreement with the MSW-LMA hypothesis and disfavours at more than 8.5 σ the so-called LOW region of the oscillation parameter space.

Precision measurement of the7Be solar neutrino flux and its day-night asymmetry with Borexino

Borexino measures the 7Be solar neutrino flux on 740 live days of data-taking to be 46±1.5+1.6−1.5 events/(day · 100 tons) which corresponds to an equivalent unoscillated flux on Earth of (3.11±0.10+0.11−0.10)·109sec −1 cm−2. This result excludes the no-oscillation hypothesis at 5 σ and provides a precise measurement of the survival probability Pee in the vacuum dominated oscillation regime Pee = 0.51±0.07. Borexino also measures the day-night asymmetry of the 7Be neutrino rate with a total error of 1.4% and finds it to be consistent with zero. This result is in agreement with the MSW-LMA hypothesis and disfavours at more than 8.5 σ the so-called LOW region of the oscillation parameter space.

High precision 7Be solar neutrinos measurement and day night effect obtained with Borexino

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso and the search for a day–night asymmetry of this interaction rate. The interaction rate of the 0.862MeV 7Be neutrinos is 46±1.6(stat)−1.6+1.5(syst) counts/(day · 100ton). The hypothesis of no oscillation for this solar neutrinos is inconsistent with our measurement at the 5.8σ C.L. Our result is the first direct measurement of solar neutrinos with an accuracy better than 5%. We report the survival probability for solar νe in the transition region between matter-enhanced and vacuum-driven oscillations. The measured day night asymmetry is Adn=0.001±0.012 (stat)±0.007 (syst), in agreement with the predicition of MSW–LMA neutrino [13] oscillations. This result discourages MSW oscillations with mixing parameters in the LOW region at more than 8.5σ, meaning that this region is, for the first time, strongly rejected without the assumption of CPT symmetry. The result can also be used to constrain some neutrino oscillation scenarios involving new physics.

Experimental evidence of electron neutrino oscillations and validation of MSW–LMA model with Borexino

We report the real time measurements of 7Be and 8B solar neutrino fluxes performed with the Borexino experiment at the Laboratori Nazionali del Gran Sasso. The achievement of these measurements was possible thanks to the excellent levels of the radiopurity reached. The measurement of the 7Be in real time is the first direct measurements of the survival probability for solar electron neutrinos in the vacuum region. For 8B we reached a threshold energy of 3MeV which is the lowest achieved so far in real time. For the first time, the same apparatus can measure two different oscillation regions (vacuum-driven and matter-enhanced) predicted by the MSW–LMA model. Borexino also quotes the ratio between the survival probabilities, corresponding to 1.93 ± 0.75, and validates the presence of the transition region between the two oscillation regimes, according to the MSW–LMA solution. In addition, a preliminary result on the Day–Night Asymmetry (ADN) for the 7Be neutrino flux is presented and corresponds to 0.007 ± 0.073. This measurement makes Borexino able to give once more an independent confirmation of the MSW–LMA solution.

First results of the Borexino experiment

Data of the Borexino experiment on the detection of the reaction involving elastic solar-neutrino scattering on an electron are presented. The fraction of electron neutrinos in the fluxes of 7Be and 8B neutrinos is in agreement with the LMA MSW oscillation solution. The uniquely low level of the Borexino detector background made it possible to set new limits on the effective magnetic moment of the neutrino, on the possible violation of the Pauli exclusion principle, and on some other rare processes.

Measurement of the solarB8neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector

We report the measurement of electron neutrino elastic scattering from 8B solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran Sasso (Italy). The rate of solar neutrino-induced electron scattering events above this energy in Borexino is 0.217 +- 0.038 (stat) +- 0.008 (syst) cpd/100 t, which corresponds to the equivalent unoscillated flux of (2.4 +- 0.4 (stat) +- 0.1 (syst))x10^6 cm^-2 s^-1, in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the 8B neutrino flux predicted by the high metallicity Standard Solar Model, the average 8B neutrino survival probability above 3 MeV is measured to be 0.29+-0.10. The survival probabilities for 7Be and 8B neutrinos as measured by Borexino differ by 1.9 sigma. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar electron neutrino survival probability between the low energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.

Results from the solar neutrino experiment BOREXINO

We report about recent results from the solar neutrino experiment BOREXINO. With BOREXINO solar neutrino spectroscopy in the sub-MeV range became possible. In particular we demonstrate the measured counting rate of solar 7Be neutrinos. Additionally we show data on solar 8B neutrinos with an energy threshold of 2.8 MeV and discuss the implications for solar and neutrino physics. Finally further prospects of BOREXINO are discussed.

KamLAND's precision measurement of neutrino oscillation parameters

The KamLAND experiment uses reactor antineutrinos to study the solar neutrino oscillation parameters. KamLAND recently updated the reactor neutrino measurement, with an almost fourfold increase of the exposure, an improved analysis technique and better understanding of the backgrounds and systematic uncertainties. Extending the analysis down to the inverse beta decay energy threshold gives a best-fit at Δm221 = 7.58+0.14-0.13(stat)+0.15-0.15(syst) × 10−5 eV2 and tan2 θ12 = 0.56+0.10-0.07(stat)+0.10-0.06(syst). Local Δχ2-minima at higher and lower Δm221 are now disfavored at >4σ. When combined with solar neutrino data, we obtain Δm221 = 7.59+0.21-0.21 × 10−5 eV2 and tan2 θ12 = 0.47+0.06-0.05. KamLAND is presently purifying the detector to measure solar 7Be neutrinos in the near future.

New results on solar neutrino fluxes from 192 days of Borexino data

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49±3stat±4syst counts/(day·100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4σ C.L. Our result is the first direct measurement of the survival probability for solar νe in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar νe, and the limit on the effective neutrino magnetic moment using solar neutrinos.

Cosmogenic 11C tagging in organic liquid scintillators

Borexino is a liquid scintillator based detector designed to measure the flux of sub-MeV solar neutrinos. Along with the recently published measurement of the 7Be neutrino, Borexino also has the potential to detect neutrinos from the pep fusion process and the CNO cycle. The observation of pep and CNO neutrinos relies on the suppression of the dominant background from cosmogenic 11C. We have been able to effectively tag 11C decays using the three-fold coincidence between the parent muon and the capture of the associated neutron on protons. This procedure will allow us to make the first real time measurements of the pep and CNO solar neutrino flux.

Direct Measurement of theBe7Solar Neutrino Flux with 192 Days of Borexino Data

We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos.

The Borexino experiment liquid scintillator purification and containment system

Borexino is a large volume, real-time, liquid scintillator detector located at the Gran Sasso National Laboratory in Italy. The principal objective of the detector is to measure mono energetic (862 keV) 7Be neutrinos from the sun present with a count rate of several tens of events per day. Measurement at this level requires an extremely low internal background due to natural radioactivity present in the detector components. In this paper the techniques used by Borexino to purify the scintillator and to build the nylon containment vessels are described. The unprecedented high radiopurity reached by Borexino permitted for the first time the realtime detection of 7Be neutrinos from the sun[1].

KamLAND status for solar neutrino phase

KamLAND has been trying to reduce backgrounds to observe neutrinos from the Sun. The first activities for the 7Be neutrino observation was performed form the spring to the summer of 2007. We report the status of the purification campaign and also describe studies for CNO neutrino measurement.

First real time detection of 7Be solar neutrinos by Borexino

This Letter reports a direct measurement of the 7Be solar neutrino signal rate performed with the Borexino low background liquid scintillator detector at the Laboratori Nazionali del Gran Sasso. This is the first real-time spectral measurement of sub-MeV solar neutrinos. The result for 0.862 MeV 7Be neutrinos is 47±7stat±12sys counts/(day ⋅ 100 ton), consistent with predictions of Standard Solar Models and neutrino oscillations with LMA-MSW parameters.

Artificial neutrino source based on the 37Ar isotope

In April 2004, a neutrino source was produced by irradiating a 330-kg piece of pressed calcium oxide at the fast-neutron reactor BN-600 (Zarechny, Russia) for six months. The 37Ar isotope was obtained via the (n, α) reaction on 40Ca, and 37Ar was extracted from an aqueous solution of nitric acid in which the solid target was dissolved. After that, 37Ar was purified and sealed into a capsule. This source was used to measure the neutrino-capture rate in metalic gallium for neutrinos from 37Ar decay, which have an energy close to that of the main line of solar 7Be neutrinos (863 keV). The target of the SAGE Gallium-Germanium Neutrino Telescope was irradiated by using this source at the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences). The source activity was measured by several methods during its production, in the course of irradiation, and after its completion. The weighted mean of the activity for six measurements was 409 ± 2 kCi at the beginning of irradiation of the gallium target (04:00 Moscow time, 30.04.2004). The scatter in the activity values obtained by different methods does not exceed 5%.