Standard Solar Model Prediction Research Articles

Shedding light on neutrino self-interactions with solar antineutrino searches

Solar antineutrinos are absent in the standard solar model prediction. Consequently, solar antineutrino searches emerge as a powerful tool to probe new physics capable of converting neutrinos into antineutrinos. In this study, we highlight that neutrino self-interactions, recently gaining considerable attention due to their cosmological and astrophysical implications, can lead to significant solar antineutrino production. We systematically explore various types of four-fermion effective operators and light scalar mediators for neutrino self-interactions. By estimating the energy spectra and event rates of solar antineutrinos at prospective neutrino detectors such as JUNO, Hyper-Kamiokande, and THEIA, we reveal that solar antineutrino searches can impose stringent constraints on neutrino self-interactions and probe the parameter space favored by the Hubble tension.

First Directional Measurement of Sub-MeV Solar Neutrinos with Borexino.

We report the measurement of sub-MeV solar neutrinos through the use of their associated Cherenkov radiation, performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The measurement is achieved using a novel technique that correlates individual photon hits of events to the known position of the Sun. In an energy window between 0.54 to 0.74MeV, selected using the dominant scintillation light, we have measured 10 887_{-2103}^{+2386}(stat)±947(syst) (68%confidence interval) solar neutrinos out of 19 904 total events. This corresponds to a ^{7}Be neutrino interaction rate of 51.6_{-12.5}^{+13.9} counts/(day·100 ton), which is in agreement with the standard solar model predictions and the previous spectroscopic results of Borexino. The no-neutrino hypothesis can be excluded with >5σ confidence level. For the first time, we have demonstrated the possibility of utilizing the directional Cherenkov information for sub-MeV solar neutrinos, in a large-scale, high light yield liquid scintillator detector. This measurement provides an experimental proof of principle for future hybrid event reconstruction using both Cherenkov and scintillation signatures simultaneously.

Constraints on flavor-diagonal non-standard neutrino interactions from Borexino Phase-II

The Borexino detector measures solar neutrino fluxes via neutrino-electron elastic scattering. Observed spectra are determined by the solar-νe survival probability Pee(E), and the chiral couplings of the neutrino and electron. Some theories of physics beyond the Standard Model postulate the existence of Non-Standard Interactions (NSI’s) which modify the chiral couplings and Pee(E). In this paper, we search for such NSI’s, in particular, flavor-diagonal neutral current interactions that modify the νee and ντe couplings using Borexino Phase II data. Standard Solar Model predictions of the solar neutrino fluxes for both high- and low-metallicity assumptions are considered. No indication of new physics is found at the level of sensitivity of the detector and constraints on the parameters of the NSI’s are placed. In addition, with the same dataset the value of sin2θW is obtained with a precision comparable to that achieved in reactor antineutrino experiments.

New Solar Metallicity Measurements

In the past years, a systematic downward revision of the metallicity of the Sun has led to the “solar modeling problem”, namely the disagreement between predictions of standard solar models and inferences from helioseismology. Recent solar wind measurements of the metallicity of the Sun, however, provide once more an indication of a high-metallicity Sun. Because of the effects of possible residual fractionation, the derived value of the metallicity Z ⊙ = 0 . 0196 ± 0 . 0014 actually represents a lower limit to the true metallicity of the Sun. However, when compared with helioseismological measurements, solar models computed using these new abundances fail to restore agreement, owing to the implausibly high abundance of refractory (Mg, Si, S, Fe) elements, which correlates with a higher core temperature and hence an overproduction of solar neutrinos. Moreover, the robustness of these measurements is challenged by possible first ionization potential fractionation processes. I will discuss these solar wind measurements, which leave the “solar modeling problem” unsolved.

Low-energy electronic recoil in xenon detectors by solar neutrinos

Low-energy electronic recoil caused by solar neutrinos in multi-ton xenon detectors is an important subject not only because it is a source of the irreducible background for direct searches of weakly-interacting massive particles (WIMPs), but also because it provides a viable way to measure the solar pp and 7Be neutrinos at the precision level of current standard solar model predictions. In this work we perform ab initio many-body calculations for the structure, photoionization, and neutrino-ionization of xenon. It is found that the atomic binding effect yields a sizable suppression to the neutrino-electron scattering cross section at low recoil energies. Compared with the previous calculation based on the free electron picture, our calculated event rate of electronic recoil in the same detector configuration is reduced by about 23%. We present in this paper the electronic recoil rate spectrum in the energy window of 100 eV to 30 keV with the standard per ton per year normalization for xenon detectors, and discuss its implication for low energy solar neutrino detection as the signal and WIMP search as a source of background.

The Sun and solar neutrinos

We present the predictions of updated standard solar models and we briefly discuss the solar composition problem, i.e. the conflict between helioseismology and standard solar models implementing the state-of-the-art photospheric abundances, emphasizing the importance of measuring neutrinos produced in the CNO cycle for its comprehension.

Asymmetric dark matter in the Sun and diphoton excess at the LHC

It has been recently pointed out that a momentum-dependent coupling of the asymmetric Dark Matter (ADM) with nucleons can explain the broad disagreement between helioseismological observables and the predictions of standard solar models. In this paper, we propose a minimal simplified ADM model consisting of a scalar and a pseudoscalar mediator, in addition to a Dirac fermionic DM, for generating such momentum-dependent interactions. Remarkably, the pseudoscalar with mass around 750 GeV can simultaneously explain the solar anomaly and the recent diphoton excess observed by both ATLAS and CMS experiments in the early $\sqrt s=13$ TeV LHC data. In this framework, the total width of the resonance is naturally large, as suggested by the ATLAS experiment, since the resonance mostly decays to the ADM pair. The model predicts the existence of a new light scalar in the GeV range, interacting with quarks, and observable dijet, monojet and $t\bar{t}$ signatures for the 750 GeV resonance at the LHC.

The impact of Borexino on the solar and neutrino physics

The Borexino detector is characterized by a very low background level due to an unprecedented radio-purity, which allows to study the entire spectrum of solar neutrinos from very low energies (∼150 keV). The solar neutrino rates from pp, 7Be, pep, 8B (with a threshold down to 3 MeV) and a stringent limit of the CNO cycle rate have been already measured. In addition evidences of a null day/night asymmetry and of the solar neutrino flux seasonal variation have been reached.The contribution provided until now by Borexino in understanding the neutrino oscillation phenomenon concerns the first evidence of the oscillation in vacuum and the determination of the νe survival probability in vacuum: these results validate the paradigmatic MSW model in the vacuum regime.The Borexino results are also in good agreement with the Standard Solar Model predictions, but the metallicity puzzle is still unsolved. In addition the pp flux measured by Borexino shows a good agreement with the Solar luminosity.Evidence of geo-neutrinos has been also obtained at the level of 5.9σ C.L.Borexino is still taking data in order to: upgrade the precision of the solar neutrino rates already measured, increase the sensitivity to the neutrino flux from the CNO cycle and hopefully measure it (very challenging), and test the existence of very short base-line neutrino oscillations.

Be7solar neutrino measurement with KamLAND

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.

FIRST NEW SOLAR MODELS WITH OPAS OPACITY TABLES

Stellar seismology appears more and more as a powerful tool for a better determination of the fundamental properties of solar-type stars. However the particular case of Sun is still challenging. The helioseismic sound speed determination continues to disagree with the Standard Solar Model (SSM) prediction for about a decade, questioning the reliability of this model. One of the sources of uncertainty could be in the treatment of the transport of radiation from the solar core to the surface. In this letter, we use the new OPAS opacity tables, recently available for solar modelling, to address this issue. We discuss first the peculiarities of these tables, then we quantify their impact on the solar sound speed and density profiles using the reduced OPAS tables taken on the grids of the OPAL ones. We use the two evolution codes MESA and CLES that led to similar conclusions in the solar radiative zone. In comparison to commonly used OPAL opacity tables, the new solar models computed, for the most recent photospheric composition, with OPAS tables present improvements in the location of the base of the convective zone and in the description of the solar radiative zone in comparison to the helioseismic observations, even if the differences in the Rosseland mean opacity do not exceed 6 %. We finally carry out a comparison to a solar model computed with the OP opacity tables.

7Be solar neutrino observation with KamLAND

The result of 7Be solar neutrino observation with KamLAND was reviewed based on the latest KamLAND publication [A. Gando et al., (KamLAND collaboration), arXiv:1405.6190 (2014)]. Prior to the observation, the 4 orders of reduction of significant background sources against 7Be solar neutrinos; 210Bi, 210Po, (and their mother isotopes), 85Kr and 40K were done by means of fractional distillation and nitrogen purging. Even though the fiducial volume had faced background intrusions due to convection of the liquid scintillator, 165.4 kton⋅days exposure within 616 days livetime leads 7Be solar neutrino rate as 582±90(kton⋅days)−1. With analysis based on a global three flavor neutrino oscillation, 7Be solar neutrino flux is interpreted as (5.82±0.98)×109 cm−2s−1, which confirms the consistency to the standard solar model predictions.

Astrophysical implications of the proton–proton cross section updates

The p(p,e+νe)H2 reaction rate is an essential ingredient for theoretical computations of stellar models. In the past several values of the corresponding S-factor have been made available by different authors. Prompted by a recent evaluation of S(E), we analysed the effect of the adoption of different proton–proton reaction rates on stellar models, focusing, in particular, on the age of mid and old stellar clusters (1–12 Gyr) and on standard solar model predictions. By comparing different widely adopted p(p,e+νe)H2 reaction rates, we found a maximum difference in the temperature regimes typical of main sequence hydrogen-burning stars (5×106–3×107 K) of about 3%. Such a variation translates into a change of cluster age determination lower than 1%. A slightly larger effect is observed in the predicted solar neutrino fluxes with a maximum difference, in the worst case, of about 8%. Finally we also notice that the uncertainty evaluation of the present proton–proton rate is at the level of few ‰, thus the p(p,e+νe)H2 reaction rate does not constitute anymore a significant uncertainty source in stellar models.

New opacity measurement principle for LMJ-PETAL laser facility

Stellar seismology reveals some interior properties of thousands of solar-type stars but the solar seismic sound speed stays puzzling since a decade as it disagrees with the Standard Solar Model (SSM) prediction. One of the explanations of this disagreement may be found in the treatment of the transport of radiation from the solar core to the surface. As the same framework is used for other stars, it is important to check precisely the reliability of the interacting cross sections of photons with each species in order to ensure the energy transport for temperature T > 2–106 K and density ρ > 0.2 g/cm3. In this paper, we propose a new technique to reach the domain of temperature and density found in the solar radiative interior. This technique called the Double Ablation Front (DAF) is based on a high conversion of the laser energy into X-rays thanks to moderated Z material irradiated by laser intensity between 1.5 × 1015 W/cm2 and 4 × 1015 W/cm2. This high conversion creates, in addition to the electronic front a second ablation front in the moderated Z material. Between the two fronts there is a plateau of density and temperature that we exploit to heat a sample of iron or of oxide. The first simulations realized with the hydrodynamic code CHIC show that this technique allows to reach conditions equivalent to half the radiative zone of the Sun with high stability both in time and space. We examine the possibility to measure both iron and oxygen absorption spectra.

Using the standard solar model to constrain solar composition and nuclear reactionSfactors

While standard solar model (SSM) predictions depend on approximately 20 input parameters, SSM neutrino flux predictions are strongly correlated with a single model output parameter, the core temperature $T_c$. Consequently, one can extract physics from solar neutrino flux measurements while minimizing the consequences of SSM uncertainties, by studying flux ratios with appropriate power-law weightings tuned to cancel this $T_c$ dependence. We re-examine an idea for constraining the primordial C+N content of the solar core from a ratio of CN-cycle $^{15}$O to pp-chain $^8$B neutrino fluxes, showing that nonnuclear SSM uncertainties in the ratio are small and effectively governed by a single parameter, the diffusion coefficient. We point out that measurements of both CN-I cycle neutrino branches -- $^{15}$O and $^{13}$N $\beta$-decay -- could in principle lead to separate determinations of the core C and N abundances, due to out-of-equilibrium CN-cycle burning in the cooler outer layers of the solar core. Finally, we show that the strategy of constructing "minimum uncertainty" neutrino flux ratios can also test other properties of the SSM. In particular, we demonstrate that a weighted ratio of $^7$Be and $^8$B fluxes constrains a product of S-factors to the same precision currently possible with laboratory data.

News from the opacity consortium OPAC

The international OPAC consortium (see list below) was formed three years ago. It is composed of astrophysicists, plasma physicists and experimentalists from different laboratories b . This consortium examines specific opacity calculations used in stellar physics. They contribute to solve the problems suggested by the astrophysical community in performing new calculations and new experiments with laser installation. We show here the specific example of the iron opacity peak that plays an important role in the envelope of intermediate-mass and massive stars and we present our first conclusions on iron and nickel. 1. OPEN PROBLEMS COMING FROM SEISMIC OBSERVATIONS The stellar community hopes to progress on the internal dynamics of stars thanks to the space-borne seismic missions SoHO, CoRoT and Kepler. But good identification and interpretation of acoustic frequencies are based on a proper microscopic physics. Along the last decade, some questions on energy transfer, linked to plasma opacities, have arisen and two cases have retained our attention. 1. The extraction of the solar internal sound speed and density has revealed clear discrepancies with the Standard Solar Model predictions (1-3). These discrepancies are not explained by the transport of momentum by rotation during the main sequence evolution (4). So the energy balance and (or) energy transfer stay clearly under suspicion. In parallel, the recent OPAS calculations (5) have revealed large differences in individual element spectra with previous calculations and in particular with OP (6, 7). OPAS calculations also show some compensation effects between low Z nuclei and the iron group contributions in the Rosseland mean opacity values. All these facts encourage further works and experimental verifications. 2. The second case concerns massive stars. SPB and Cephei stars are interesting pulsators that might put important constraints on rotation and magnetic fields, two key actors for massive stars. Presently, the 40 stars observed by Kepler show acoustic and gravity modes probably up to � = 20 (deformed stars) that are difficult to identify (8). The first difficulty comes from the iron group opacities, which drive their pulsations. The observed modes do not agree with the stability of modes deduced from the OP or OPAL tables (9), which suggests that those opacities are underestimated (10, 11). Up to now, our effort is dedicated to the second case. The first analysis of the OPAC consortium confirms an underestimate of these opacities through comparison with more recent opacity calculations based on old and new measurements (12-15). We shall here present our first conclusions and new orientations for the coming years.

Measurements of 8B Solar Neutrinos – Results and Prospects from SNO and SuperKamiokande

Measurements of 8 B solar neutrinos at the Sudbury Neutrino Observatory (SNO) and at SuperKamiokande (SK) result in a model independent proof that electron neutrinos born in the Sun undergo active flavor transformation. Large mixing angle, matter enhanced neutrino oscillations are responsible for this flavor transformation and the total flux of 8 B solar neutrinos measured is in agreement with standard solar model predictions. The long-standing solar neutrino problem is resolved. In this paper the salient results from measurements of 8 B solar neutrinos at SNO and SK are summarized, including recent analyses looking for potential temporal variations in the solar neutrino fluxes and a new limit on the hep solar neutrino flux. The field of solar neutrino physics has entered a new era of precision with measurements aimed at the elucidation of fundamental neutrino properties and our basic understanding of how the Sun shines. Future goals and prospects of the SNO and SK experiments are discussed.

Measurement of the8B solar neutrino flux with the KamLAND liquid scintillator detector

We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5-MeV analysis threshold is 1.49 ± 0.14(stat) ± 0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77 ± 0.26(stat) ± 0.32(syst) ×106 cm−2s−1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with standard solar model predictions which include matter-enhanced neutrino oscillation.Received 8 June 2011DOI:https://doi.org/10.1103/PhysRevC.84.035804©2011 American Physical Society

LINEAR SOLAR MODELS

We present a new approach to study the properties of the sun. We consider small variations of the physical and chemical properties of the sun with respect to Standard Solar Model predictions and we linearize the structure equations to relate them to the properties of the solar plasma. By assuming that the (variation of) the present solar composition can be estimated from the (variation of) the nuclear reaction rates and elemental diffusion efficiency in the present sun, we obtain a linear system of ordinary differential equations which can be used to calculate the response of the sun to an arbitrary modification of the input parameters (opacity, cross sections, etc.). This new approach is intended to be a complement to the traditional methods for solar model calculation and allows to investigate in a more efficient and transparent way the role of parameters and assumptions in solar model construction. We verify that these Linear Solar Models recover the predictions of the traditional solar models with an high level of accuracy.

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.

Determination of theνeand totalB8solar neutrino fluxes using the Sudbury Neutrino Observatory Phase I data set

This article provides the complete description of results from the Phase I data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is based on a 0.65 kt-year exposure of heavy water to the solar $^8$B neutrino flux. Included here are details of the SNO physics and detector model, evaluations of systematic uncertainties, and estimates of backgrounds. Also discussed are SNO's approach to statistical extraction of the signals from the three neutrino reactions (charged current, neutral current, and elastic scattering) and the results of a search for a day-night asymmetry in the $\nu_e$ flux. Under the assumption that the $^8$B spectrum is undistorted, the measurements from this phase yield a solar $\nu_e$ flux of $\phi(\nu_e) = 1.76^{+0.05}_{-0.05}{(stat.)}^{+0.09}_{-0.09} {(syst.)} \times 10^{6}$ cm$^{-2}$ s$^{-1}$, and a non-$\nu_e$ component $\phi(\nu_{\mu\tau}) = 3.41^{+0.45}_{-0.45}{(stat.)}^{+0.48}_{-0.45} {(syst.)} \times 10^{6}$ cm$^{-2}$ s$^{-1}$. The sum of these components provides a total flux in excellent agreement with the predictions of Standard Solar Models. The day-night asymmetry in the $\nu_e$ flux is found to be $A_{e} = 7.0 \pm 4.9 \mathrm{(stat.)^{+1.3}_{-1.2}}% \mathrm{(sys.)}$, when the asymmetry in the total flux is constrained to be zero.