Measurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector
O. Y. Smirnov, M. Agostini, S. Appel, G. Bellini, J. Benziger, D. Bick, G. Bonfini, D. Bravo, B. Caccianiga, F. Calaprice, A. Caminata, P. Cavalcante, A. Chepur… 展开作者
O. Y. Smirnov, M. Agostini, S. Appel, G. Bellini, J. Benziger, D. Bick, G. Bonfini, D. Bravo, B. Caccianiga, F. Calaprice, A. Caminata, P. Cavalcante, A. Chepurnov, K. Choi, D. D'Angelo, S. Davini, A. Derbin, L. Di Noto, I. Drachnev, A. Empl, A. Etenko, K. Fomenko, D. Franco, F. Gabriele, C. Galbiati, C. Ghiano, M. Giammarchi, M. Goeger-Neff, A. Goretti, M. Gromov, C. Hagner, E. Hungerford, Aldo Ianni, Andrea Ianni, K. Jedrzejczak, M. Kaiser, V. Kobychev, D. Korablev, G. Korga, D. Kryn, M. Laubenstein, B. Lehnert, E. Litvinovich, F. Lombardi, P. Lombardi, L. Ludhova, G. Lukyanchenko, I. Machulin, S. Manecki, W. Maneschg, S. Marcocci, E. Meroni, M. Meyer, L. Miramonti, M. Misiaszek, P. Mosteiro, V. Muratova, B. Neumair, L. Oberauer, M. Obolensky, F. Ortica, K. Otis, L. Pagani, M. Pallavicini, L. Papp, L. Perasso, A. Pocar, G. Ranucci, A. Razeto, A. Re, A. Romani, R. Roncin, N. Rossi, S. Schönert, D. Semenov, H. Simgen, M. Skorokhvatov, A. Sotnikov, S. Sukhotin, Y. Suvorov, R. Tartaglia, G. Testera, J. Thurn, M. Toropova, E. Unzhakov, R. B. Vogelaar, F. von Feilitzsch, H. Wang, S. Weinz, J. Winter, M. Wojcik, M. Wurm, Z. Yokley, O. Zaimidoroga, S. Zavatarelli, K. Zuber, G. Zuzel
Neutrino produced in a chain of nuclear reactions in the Sun starting from the fusion of two protons, for the first time has been detected in a real-time detector in spectrometric mode. The unique properties of the Borexino detector provided an oppurtunity to disentangle pp-neutrino spectrum from the background components. A comparison of the total neutrino flux from the Sun with Solar luminosity in photons provides a test of the stability of the Sun on the 10$^{5}$ years time scale, and sets a strong limit on the power production in the unknown energy sources in the Sun of no more than 4\% of the total energy production at 90\% C.L.
Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso in Italy. Since the start of its data taking in May 2007, it has provided several measurements of low-energy neutrinos from various sources. At the base of its success, lie unprecedented levels of radio-purity and extensive thermal stabilisation, both resulting from a years-long effort of the collaboration. Solar neutrinos, emitted in the hydrogen-to-helium fusion in the solar core, are important for the understanding of our star, as well as neutrino properties. Borexino is the only experiment…
The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. The primary reaction is the fusion of two protons into a deuteron, a positron and a neutrino. These neutrinos constitute the vast majority of neutrinos reaching Earth, providing us with key information about what goes on at the core of our star. Several experiments have now confirmed the observation of neutrino oscillations by detecting neutrinos from secondary nuclear processes in the Sun; this is the first direct spectral measurement of the neutrinos from the keystone proton-proton fusion. This ob…
The main goal of the Borexino detector, in its final phase of construction in the Gran Sasso underground laboratory, is the direct observation and measurement of the low energy component of neutrinos coming from the Sun. The unique low energy sensitivity and ultra-low background bring new capabilities to attack problems in neutrino physiscs other than solar ones. Investigation about the study of Supernoavae neutrinos and neutrino coming from the Earth (Geoneutrinos) are here resumed.
Borexino is a massive calorimetric liquid scintillation detector whose installation has been completed in the underground Gran Sasso Laboratory. The focus of the experiment is on the direct and real time measurement of the flux of neutrinos produced in the $^{7}Be$ electron capture reaction in the Sun. Furthermore, recent studies about the reduction of the $^{11}C$ background through suitable rejection techniques demonstrated the possibility to open an interesting additional observation window in the energy region of the pep and CNO solar neutrinos. Beyond the solar neutrino program, the detec…
Measuring all neutrino components is the most direct way to test the standard solar model (SSM). Despite the great results obtained so far, important questions such as the solar metallicity remain open. A precise measurement of the solar pp chain and the CNO cycle would settle this controversy between high (HZ) and low (LZ) metallicity compositions of the Sun. Solar neutrinos allow the determination of oscillation parameters, in particular the $θ_{12}$ mixing angle and, to a lesser degree the $Δm^2_{12}$ mass splitting. Furthermore the measurement of the electron neutrino survival probability …
We report on the search for anti-neutrinos of yet unknown origin with the Borexino detector at the Laboratori Nazionali del Gran Sasso. In particular, a hypothetical anti-neutrino flux from the Sun is investigated. Anti-neutrinos are detected through the neutron inverse $β$ decay reaction in a large liquid organic scintillator target. We set a new upper limit for a hypothetical solar $\barν_e$ flux of 760 ${\rm cm}^{-2}{\rm s}^{-1}$, obtained assuming an undistorted solar $^8$B energy spectrum. This corresponds to a limit on the transition probability of solar neutrinos to anti-neutrinos of $1…
We discuss the limits on the neutrino magnetic moment and hypothetical interactions with a hidden unparticle sector, coming from the first neutrino data release of the Borexino experiment. The observed spectrum in Borexino depends weakly on the solar model used in the analysis, since most of the signal comes from the mono-energetic 7Be neutrinos. This fact allows us to calibrate the nu-e scattering cross section through the spectral shape. In this way, we have derived a limit on the magnetic moment for the neutrinos coming from the Sun (in which a nu_mu and nu_tau component is present): mu_nu<…
We present the most recent results from the two currently running solar neutrino experiments, Borexino at the Gran Sasso laboratory in Italy and SuperK at Kamioka mine in Japan. SuperK has released the most precise yet measurement of the 8B solar neutrino interaction rate, with a precision better than 2\%, consistent with a constant solar neutrino emission over more than a decade. Borexino has released refined measurements of all neutrinos produced in the pp fusion chain. For the first time, one single detector has measured the entire range of solar neutrinos at once. These new data weakly fav…
Borexino is an experiment for low energy neutrino spectroscopy at the Gran Sasso underground laboratories. It is designed to measure the mono-energetic $^7$Be solar neutrino flux in real time, via neutrino-electron elastic scattering in ultra-pure organic liquid scintillator. Borexino has the potential to also detect neutrinos from the \emph{pep} fusion process and the CNO cycle. For this measurement to be possible, radioactive contamination in the detector must be kept extremely low. Once sufficiently clean conditions are met, the main background source is $^{11}$C, produced in reactions indu…
We explore the implications of the Borexino experiment's real time measurements of the lowest energy part of the neutrino spectrum from the primary pp fusion process up to 0.420 MeV through the 7^Be decay at 0.862 MeV to the pep reaction at 1.44 MeV. We exploit the fact that at such low energies, the large mixing angle solution to the Mikheyev-Smirnov-Wolfenstein matter effects in the sun are small for 7^Be and pep and negligible for pp. Consequently, the neutrinos produced in the sun change their flavor almost entirely through vacuum oscillations during propagation from the sun's surface and …
Neutrinos are elementary particles which are known since many years as fundamental messengers from the interior of the Sun. The Standard Solar Model, which gives a theoretical description of all nuclear processes which happen in our star, predicts that roughly 99% of the energy produced is coming from a series of processes known as the "pp chain". Such processes have been studied in detail over the last years by means of neutrinos, thanks also to the important measurements provided by the Borexino experiment. The remaining 1% is instead predicted to come from a separate loop-process, known as …
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 MeV to 0.74 MeV, selected using the dominant scintillation light, we have measured 10887$^{+2386}_{-2103} (\mathrm{stat.})\pm 947 (\mathrm{syst.})$ ($68\%$ confidence interval) solar neutrinos out of 19904 total events. This corresponds to a…
Standard solar models (SSMs) provide a reference framework across a number of research fields: solar and stellar models, solar neutrinos, particle physics the most conspicuous among them. The accuracy of the physical description of the global properties of the Sun that SSMs provide has been challenged in the last decade by a number of developments in stellar spectroscopic techniques. Over the same period of time, solar neutrino experiments, and Borexino in particular, have measured the four solar neutrino fluxes from the pp-chains that are associated with 99\% of the nuclear energy generated i…
If heavy neutrinos with mass $m_{ν_{H}}\geq$2$ m_e $ are produced in the Sun via the decay ${^8\rm{B}} \rightarrow {^8\rm{Be}} + e^+ + ν_H$ in a side branch of pp-chain, they would undergo the observable decay into an electron, a positron and a light neutrino $ν_{H}\rightarrowν_{L}+e^++e^-$. In the present work Borexino data are used to set a bound on the existence of such decays. We constrain the mixing of a heavy neutrino with mass 1.5 MeV $\leq m_{ν_{H}} \le$ 14 MeV to be $|U_{eH}|^2\leq (10^{-3}-4\times10^{-6})$ respectively. These are tighter limits on the mixing parameters than obtained …
Neutrinos emitted in the carbon, nitrogen, oxygen (CNO) fusion cycle in the Sun are a sub-dominant, yet crucial component of solar neutrinos whose flux has not been measured yet. The Borexino experiment at the Laboratori Nazionali del Gran Sasso (Italy) has a unique opportunity to detect them directly thanks to the detector's radiopurity and the precise understanding of the detector backgrounds. We discuss the sensitivity of Borexino to CNO neutrinos, which is based on the strategies we adopted to constrain the rates of the two most relevant background sources, pep neutrinos from the solar pp-…
Borexino is a liquid scintillator detector located at the Laboratori Nazionale del Gran Sasso, Italy with the main goal to measure solar neutrinos. The experiment recently provided the first direct experimental evidence of CNO-cycle neutrinos in the Sun, rejecting the no-CNO signal hypothesis with a significance greater than 5$σ$ at 99\%C.L. The intrinsic $^{210}$Bi is an important background for this analysis due to its similar spectral shape to that of CNO neutrinos. $^{210}$Bi can be measured through its daughter $^{210}$Po which can be distinguished through an event-by-event basis via puls…
Liquid scintillator detectors play a central role in the detection of neutrinos from various sources. In particular, it is the only technique used so far for the precision spectroscopy of sub-MeV solar neutrinos, as demonstrated by the Borexino experiment at the Gran Sasso National Laboratory in Italy. The benefit of a high light yield, and thus a low energy threshold and a good energy resolution, comes at the cost of the directional information featured by water Cherenkov detectors, measuring $^8$B solar neutrinos above a few MeV. In this paper we provide the first directionality measurement …
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 o…
We present an improved measurement of the CNO solar neutrino interaction rate at Earth obtained with the complete Borexino Phase-III dataset. The measured rate R$_{\rm CNO}$ = $6.7^{+2.0}_{-0.8}$ counts/(day$ \cdot$ 100 tonnes), allows us to exclude the absence of the CNO signal with about 7$σ$ C.L. The correspondent CNO neutrino flux is $6.6^{+2.0}_{-0.9} \times 10^8$ cm$^{-2}$ s$^{-1}$, taking into account the neutrino flavor conversion. We use the new CNO measurement to evaluate the C and N abundances in the Sun with respect to the H abundance for the first time with solar neutrinos. Our re…
We show that solar neutrino experiments set an upper limit of 7.8% (7.3% including the recent KamLAND measurements) to the fraction of energy that the Sun produces via the CNO fusion cycle, which is an order of magnitude improvement upon the previous limit. New experiments are required to detect CNO neutrinos corresponding to the 1.5% of the solar luminosity that the standard solar model predicts is generated by the CNO cycle.
Shanghai Jiao Tong University（上海交通大学）；SJTU Paris Elite Institute of Technology, Shanghai Jiao Tong University（上海交大巴黎卓越工程师学院）；Shanghai Jiao Tong University Sichuan Research Institute（上海交通大学四川研究院）
We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ($\barν_e$) are detected in an organic liquid scintillator through the inverse $β$-decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $\barν_e$ fluxes in t…
Solar neutrino experiments are highly sensitive to sources of $ν\to\overlineν$ conversions in the $^8$B neutrino flux. In this work we adapt these searches to non-minimal sterile neutrino models recently proposed to explain the LSND, MiniBooNE, and reactor anomalies. The production of such sterile neutrinos in the Sun, followed the decay chain $ν_4 \to νϕ\to νν\overlineν$ with a new scalar $ϕ$ results in upper limits for the neutrino mixing $|U_{e4}|^2$ at the per mille level. We conclude that a simultaneous explanations of all anomalies is in tension with KamLAND, Super-Kamiokande, and Borexi…
This paper reviews the constraints on the solar neutrino mixing parameters with data collected by the Homestake, SAGE, GALLEX, Kamiokande, SuperKamiokande, Borexino and SNO experiments. An emphasis will be given to the global solar neutrino analyses in terms of matter-enhanced oscillation of two and three active flavors. The results to-date, including both solar model dependent and independent measurements, indicate that electron neutrinos are changing to other active types on route to the Earth from the Sun. The total flux of solar neutrinos is found to be in very good agreement with solar mo…
Next-generation experiments allow for the possibility to testing the neutrino flavor oscillation model to very high levels of accuracy. Here, we explore the possibility that the dark matter in the current universe is made of two particles, a sterile neutrino and a very light dark matter particle. By using a 3+1 neutrino flavor oscillation model, we study how such a type of dark matter imprints the solar neutrino fluxes, spectra, and survival probabilities of electron neutrinos. The current solar neutrino measurements allow us to define an upper limit for the ratio of the mass of a light dark m…
For most of their existence stars are fueled by the fusion of hydrogen into helium proceeding via two theoretically well understood processes, namely the $pp$ chain and the CNO cycle. Neutrinos emitted along such fusion processes in the solar core are the only direct probe of the deep interior of the star. A complete spectroscopy of neutrinos from the {\it pp} chain, producing about 99\% of the solar energy, has already been performed \cite{bib:Nature-2018}. Here, we report the direct observation, with a high statistical significance, of neutrinos produced in the CNO cycle in the Sun. This is …
We explore the effects of nonstandard neutrino interactions in the lower components of the solar neutrino spectrum which are predominant by the vacuum oscillations. The recent measurements of Borexino experiment between 2011 and 2015 provide a clean test to study the nonstandard neutrino interactions at the source (sun) and the at solar detector. In this work, first the possible standard model parameters are estimated from the combined data of the low energy regime and then the nonstandard effects at the source, at the detector, and from the interplay between source and detector parameters are…
We present updated standard solar models (SSMs) that incorporate the latest results for nuclear fusion rates, recently published. We show helioseismic results for high and low metallicity compositions and also for an alternative set of solar abundance, derived from 3D model atmospheres, which give intermediate results. For the high and low metallicity models, we show that current solar neutrino data can not differentiate between models and that a measurement of the CNO fluxes is necessary to achieve that goal. A few additional implications of a hypothetical measurement of CNO neutrinos, both i…
We describe the current status of solar neutrino measurements and of the theory -- both neutrino physics and solar astrophysics -- employed in interpreting measurements. Important recent developments include Super-Kamiokande's determination of the neutrino-electron elastic scattering rate for 8B neutrinos to 3%; the latest SNO global analysis in which the inclusion of low-energy data from SNO I and II significantly narrowed the range of allowed values for the neutrino mixing angle theta12; Borexino results for both the 7Be and pep neutrino fluxes, the first direct measurements constraining the…
Several next-generation experiments aim to make the first measurement of the neutrino flux from the Carbon-Nitrogen-Oxygen (CNO) solar fusion cycle. We calculate how much time these experiments will need to run for in order to measure this flux with enough precision to tell us the metal content of the Sun's core, and thereby help to solve the solar metallicity problem. For experiments looking at neutrino-electron scattering, we find that SNO+ will measure this CNO neutrino flux with enough precision after five years in its pure scintillator mode, provided its $^{210}$Bi background is measured …
The $ν$SOL experiment to operate a neutrino detector close to the Sun is building a small test detector to orbit the Earth to test the concept in space. This detector concept is to provide a new way to detect neutrinos unshielded in space. A double delayed coincidence on Gallium nuclei that have a large cross section for solar neutrino interactions emitting a conversion electron and converting the nuclei into an excited state of Germanium, which decays with a well-known energy and half-life. This unique signature permits operation of the detector volume mostly unshielded in space with a high s…
We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Se…
As is well known, dark matter direct detection experiments will ultimately be limited by a "neutrino floor," due to the scattering of nuclei by MeV neutrinos from, e.g., nuclear fusion in the Sun. Here we point out the existence of a new "neutrino floor" that will similarly limit indirect detection with the Sun, due to high-energy neutrinos from cosmic-ray interactions with the solar atmosphere. We have two key findings. First, solar atmospheric neutrinos $\lesssim 1$ TeV cause a sensitivity floor for standard WIMP scenarios, for which higher-energy neutrinos are absorbed in the Sun. This floo…
In this paper we use the conformal anomaly in QCD to derive the coupling of light radion to gluons in the Randall-Sundrum model and use it to compute the radion production cross section at hadron colliders by gluon fusion. We find that the radion production cross section by gluon fusion at LHC would exceed that of the higgs boson by a factor that lies between 7 and 8 over most of the range. The decay modes of the radion are similar to that of the SM higgs boson. But the striking feature is the enhancement of radion to 2-photon and radion to 2-gluon branching ratio over the SM case. Utilising t…
