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

Abstract

We report the measurement of ν-e elastic scattering from 8 B 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 Φ ES 8 B = 2.4 ± 0.4± 0.1×10 6 cm −2 s −1 , in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the 8 B neutrino flux predicted by the high metallicity Standard Solar Model, the average 8 B νe survival probability above 3 MeV is measured to be 0.29±0.10. The survival probabilities for 7 Be and 8 B neutrinos as measured by Borexino differ by 1.9 σ. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar νe survival probability Pee between the low energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.PACS numbers: 14.60. St, 26.65.+t, 95.55.Vj, 29.40.Mc INTRODUCTION Solar8 B-neutrino spectroscopy has been so far performed by the waterČerenkov detectors KamiokaNDE, SuperKamiokaNDE,. The first two experiments used elastic ν-e scattering for the detection of neutrinos, whereas SNO also exploited nuclear reaction channels on deuterium with heavy water as target. These experiments provided robust spectral measurements with ∼5 MeV threshold or higher for scattered electrons; a recent SNO analysis reached a 3.5 MeV threshold [5].We report the first observation of solar 8 B-neutrinos with a liquid scintillator detector, performed by the Borexino experiment [6,7] via elastic ν-e scattering. Borexino is the first experiment to succeed in suppressing all major backgrounds, above the 2.614 MeV γ from the decay of 208 Tl, to a rate below that of electron scatterings from solar neutrinos. This allows to reduce the energy threshold for scattered electrons by 8 B solar neutrinos to 3 MeV, the lowest ever reported for the electron scattering channel. To facilitate a comparison to the results of SuperKamiokaNDE [3] and SNO D 2 O phase [4], we also report the measured 8 B neutrino interaction rate with 5 MeV threshold.Since Borexino also detected low energy solar 7 Be neutri-2 nos [8,9], this is the first experiment where both branches of the solar pp-cycle have been measured simultaneously in the same target. The large mixing angle solution (LMA) of the MSW effect [10] predicts a transition in the ν e survival probability from the vacuum oscillation regime at low energies to the matter dominated regime at high energies. Results on solar 7 Be and 8 B neutrinos from Borexino, combined with prediction on the absolute neutrino fluxes from the Standard Solar Model [11][12][13], confirm that our data are in agreement with the MSW-LMA prediction within 1σ. EXPERIMENTAL APPARATUS AND ENERGY THRESHOLDThe Borexino detector is located at the underground Laboratori Nazionali del Gran Sasso (LNGS) in central Italy, at a depth of 3600 m.w.e.. Solar neutrinos are detected in Borexino exclusively via elastic ν-e scattering in a li...

A Search for Low-energy Neutrinos Correlated with Gravitational Wave Events GW 150914, GW 151226, and GW 170104 with the Borexino Detector

“…A detailed description of the detector could be found elsewhere [17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…Borexino first detected and then precisely measured the flux of the 7 Be solar neutrinos [20,21,30], has ruled out any significant day-night asymmetry of their interaction rate [26], has measured the 8 B-neutrino rate with 3 MeV threshold [23], has made the first direct observation of pep neutrinos [27], has made the first spectral measurement of pp-neutrinos [28] and has set the best upper limit on the flux of solar neutrinos produced in the CNO cycle [27]. The uniquely low background level of the Borexino detector made it possible to set new limits on the effective magnetic moment of the neutrino [21], on the stability of the electron for decay into a neutrino and a photon [31], on the heavy sterile neutrino mixing in 8 B decay [32], on the possible violation of the Pauli exclusion principle [33], on the flux of high energy solar axions [34], on antineutrinos from the Sun and other unknown sources [35], on Gamma-Ray bursts neutrino and antineutrino fluences [36] and on some other rare processes.…”

Solar neutrinos: an update

“…High energy 8 B neutrinos have been the first detected solar neutrinos in the Homestake experiment in the 60s [7]; their detection with different interaction channel in SNO led to the confirmation of solar neutrino oscillation [8] [9]. The first time detection of 8 B neutrinos with a 3 MeV threshold (kinetic energy of electron recoil) has been performed in Borexino [10]. The energy production in the CNO cycle only constitutes a small contribution to the total luminosity in the Sun (of the order of ∼ 1% in the Solar Standard Models).…”

“…Borexino reported in 2010 the measurement of electron neutrino elastic scattering from 8 B solar neutrinos with 3 MeV energy threshold [10]. 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 ton, which corresponds to the equivalent unoscillated flux of (2.4 ± 0.4(stat) ± 0.1(syst)) × 10 6 cm −2 s −1 , in good agreement with measurements from SNO and Super-KamiokaNDE.…”

Constraints and consequences of reducing small scale structure via large dark matter-neutrino interactions

“…Because the KamLAND experiment, while very constraining of ∆m 2 12 , is not as sensitive to U e2 , the theoretical calculation of the 8 B flux currently gives the best precision on this determination. Experimentally, a combination of electron scattering and neutral current measurements are used to calibrate the flux [64,65] and the sterile neutrino component could affect this. Since the 8 B flux is theoretically known to about the 15% level currently [66], we obtain a limit of |sin θ τ | 0.6.…”