The proposed large-volume detector LENA (Low Energy Neutrino Astronomy) is a multi-purpose liquid-scintillator experiment. Its sensitive mass of 50 kt allows for high-statistic measurements of ...astrophysical and terrestrial low-energy neutrino sources. Moreover, new limits might be put on the lifetime of the proton decay channel into K+ .
In the core of the Sun, energy is released through sequences of nuclear reactions that convert hydrogen into helium. The primary reaction is thought to be the fusion of two protons with the emission ...of a low-energy neutrino. These so-called pp neutrinos constitute nearly the entirety of the solar neutrino flux, vastly outnumbering those emitted in the reactions that follow. Although solar neutrinos from secondary processes have been observed, proving the nuclear origin of the Sun's energy and contributing to the discovery of neutrino oscillations, those from proton-proton fusion have hitherto eluded direct detection. Here we report spectral observations of pp neutrinos, demonstrating that about 99 per cent of the power of the Sun, 3.84 × 10(33) ergs per second, is generated by the proton-proton fusion process.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The rate of neutrino-electron elastic scattering interactions from 862 keV Be7 solar neutrinos in Borexino is determined to be 46.0±1.5(stat)-1.6+1.5(syst)counts/(day*100ton). This corresponds to a ...νe-equivalent Be7 solar neutrino flux of (3.10±0.15)×109cm-2s-1 and, under the assumption of νe transition to other active neutrino flavours, yields an electron neutrino survival probability of 0.51±0.07 at 862 keV. The no flavor change hypothesis is ruled out at 5.0σ. A global solar neutrino analysis with free fluxes determines Φpp=6.06-0.06+0.02×1010cm-2s-1 and ΦCNO<1.3×109cm-2s-1 (95% C.L.). These results significantly improve the precision with which the Mikheyev-Smirnov-Wolfenstein large mixing angle neutrino oscillation model is experimentally tested at low energy.
We observed, for the first time, solar neutrinos in the 1.0-1.5 MeV energy range. We determined the rate of pep solar neutrino interactions in Borexino to be 3.1±0.6{stat}±0.3{syst} counts/(day·100 ...ton). Assuming the pep neutrino flux predicted by the standard solar model, we obtained a constraint on the CNO solar neutrino interaction rate of <7.9 counts/(day·100 ton) (95% C.L.). The absence of the solar neutrino signal is disfavored at 99.97% C.L., while the absence of the pep signal is disfavored at 98% C.L. The necessary sensitivity was achieved by adopting data analysis techniques for the rejection of cosmogenic {11}C, the dominant background in the 1-2 MeV region. Assuming the Mikheyev-Smirnov-Wolfenstein large mixing angle solution to solar neutrino oscillations, these values correspond to solar neutrino fluxes of (1.6±0.3)×10{8} cm{-2} s^{-1} and <7.7×10{8} cm{-2} s{-1} (95% C.L.), respectively, in agreement with both the high and low metallicity standard solar models. These results represent the first direct evidence of the pep neutrino signal and the strongest constraint of the CNO solar neutrino flux to date.
Observation of geo-neutrinos Bellini, G.; Benziger, J.; Bonetti, S. ...
Physics letters. B,
04/2010, Letnik:
687, Številka:
4-5
Journal Article
Recenzirano
Odprti dostop
Geo-neutrinos, electron anti-neutrinos produced in β decays of naturally occurring radioactive isotopes in the Earth, are a unique direct probe of our planet's interior. We report the first ...observation at more than 3σ C.L. of geo-neutrinos, performed with the Borexino detector at Laboratori Nazionali del Gran Sasso. Anti-neutrinos are detected through the neutron inverse β decay reaction. With a 252.6 ton yr fiducial exposure after all selection cuts, we detected 9.9+4.1−3.4(+14.6−8.2) geo-neutrino events, with errors corresponding to a 68.3% (99.73%) C.L. From the lnL profile, the statistical significance of the Borexino geo-neutrino observation corresponds to a 99.997% C.L.
Our measurement of the geo-neutrinos rate is 3.9+1.6−1.3(+5.8−3.2) events/(100 ton yr).
The observed prompt positron spectrum above 2.6 MeV is compatible with that expected from European nuclear reactors (mean base line of approximately 1000 km). Our measurement of reactor anti-neutrinos excludes the non-oscillation hypothesis at 99.60% C.L. This measurement rejects the hypothesis of an active geo-reactor in the Earth's core with a power above 3 TW at 95% C.L.
We present a measurement of the geo-neutrino signal obtained from 1353 days of data with the Borexino detector at Laboratori Nazionali del Gran Sasso in Italy. With a fiducial exposure of ...(3.69±0.16)×1031 proton × year after all selection cuts and background subtraction, we detected (14.3±4.4) geo-neutrino events assuming a fixed chondritic mass Th/U ratio of 3.9. This corresponds to a geo-neutrino signal Sgeo=(38.8±12.0) TNU with just a 6×10−6 probability for a null geo-neutrino measurement. With U and Th left as free parameters in the fit, the relative signals are STh=(10.6±12.7) TNU and SU=(26.5±19.5) TNU. Borexino data alone are compatible with a mantle geo-neutrino signal of (15.4±12.3) TNU, while a combined analysis with the KamLAND data allows to extract a mantle signal of (14.1±8.1) TNU. Our measurement of 31.2−6.1+7.0 reactor anti-neutrino events is in agreement with expectations in the presence of neutrino oscillations.
The solar neutrino experiment Borexino, which is located in the Gran Sasso underground laboratories, is in a unique position to study muon-induced backgrounds in an organic liquid scintillator. In ...this study, a large sample of cosmic muons is identified and tracked by a muon veto detector external to the liquid scintillator, and by the specific light patterns observed when muons cross the scintillator volume. The yield of muon-induced neutrons is found to be Y sub(n) = (3.10 + or - 0.11) times 10 super(-4) sub(n)/( mu times (g/cm super(2))). The distance prole between the parent muon track and the neutron capture point has the average value lambda = (81.5 + or - 2.7) cm. Additionally the yields of a number of cosmogenic radioisotopes are measured for super(12)N, super(12)B, super(8)He, super(9)C, super(9)Li, super(8)B, super(6)He, super(8)Li, super(11)Be, super(10)C and super(11)C. All results are compared with Monte Carlo simulation predictions using the Fluka and GEANT4 packages. General agreement between data and simulation is observed for the cosmogenic production yields with a few exceptions, the most prominent case being super(11)C yield for which both codes return about 50% lower values. The predicted mu -n distance prole and the neutron multiplicity distribution are found to be overall consistent with data.
We have measured the muon flux at the underground Gran Sasso National Laboratory (3800 m w.e.) to be (3.41 + or - 0.01) times 10 super(-4)m super(-2)s super(-1) using four years of Borexino data. A ...modulation of this signal is observed with a period of (366 + or - 3) days and a relative amplitude of (1.29 + or - 0.07)%. The measured phase is (179 + or - 6) days, corresponding to a maximum on the 28 super(th) of June. Using the most complete atmospheric data models available, muon rate fluctuations are shown to be positively correlated with atmospheric temperature, with an effective coefficient alpha sub(T) = 0.93 + or - 0.04. This result represents the most precise study of the muon flux modulation for this site and is in good agreement with expectations.
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