Solar neutrino results from Borexino and main future perspectives Pallavicini, Marco; Bellini, G.; Benziger, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2011, Letnik:
630, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Borexino is a solar neutrino experiment running at the Laboratori Nazionali del Gran Sasso, Italy. The radioactive background levels in the liquid scintillator target meet or even exceed design ...goals, opening unanticipated opportunities. The main results, so far, are the measurement of the
7Be solar neutrino flux (the first ever done) and the measurement of the
8B neutrino flux performed with electron energy threshold of 2.8
MeV. The short and medium term perspectives are summarized in the conclusions.
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 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.
The equation of state plays a critical role in the physics of the merger of two neutron stars. Recent numerical simulations with a microphysical equation of state suggest the outcome of such events ...depends on the mass of the neutron stars. For less massive systems, simulations favor the formation of a hypermassive, quasistable neutron star, for which the oscillations produce a short, high-frequency burst of gravitational radiation. Its dominant frequency content is tightly correlated with the radius of the neutron star, and its measurement can be used to constrain the supranuclear equation of state. In contrast, the merger of higher mass systems results in prompt gravitational collapse to a black hole. We have developed an algorithm that combines waveform reconstruction from a morphology-independent search for gravitational wave transients with the Bayesian model selection to discriminate between postmerger scenarios and accurately measure the dominant oscillation frequency. We demonstrate the efficacy of the method using a catalog of simulated binary merger signals in data from LIGO and Virgo, and we discuss the prospects for this analysis in advanced ground-based gravitational wave detectors. From the waveforms considered in this work, we find that the postmerger neutron star signal may be detectable by this technique to ~4-12 Mpc, for sources with random sky locations and orientations with respect to the Earth. We also find that we successfully discriminate between the postmerger scenarios with ~95% accuracy and determine the dominant oscillation frequency of surviving postmerger neutron stars to within ~10 Hz, averaged over all detected signals. This leads to an uncertainty in the estimated radius of a nonrotating 1.6 M sub(odot) reference neutron star of ~100 m.
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
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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.
A 4.8 m
3 unsegmented liquid scintillation detector at the underground Laboratori Nazionali del Gran Sasso has shown the feasibility of multi-ton low-background detectors operating to energies as low ...as 250 keV. Detector construction and the handling of large volumes of liquid scintillator to minimize the background are described. The scintillator, 1.5 g PPO/L-pseudocumene, is held in a flexible nylon vessel shielded by 1000 t of purified water. The active detector volume is viewed by 100 photomultipliers, which measure time and charge for each event, from which energy, position and pulse shape are deduced. On-line purification of the scintillator by water extraction, vacuum distillation and nitrogen stripping removed radioactive impurities. Upper limits were established of < 10
−7 Bq/kg-scintillator for events with energies 250 keV <
E < 800 keV, and < 10
−9 Bq/kg-scintillator due to the decay products of uranium and thorium. The isotopic abundance of
14C
12C
in the scintillator was shown to be approximately 10
−18 by extending the energy window of the detector to 25–250 keV. The
14C abundance and uranium and thorium levels in the CTF are compatible with the Borexino Solar Neutrino Experiment.
Gravitational wave parameter inference pipelines operate on data containing unknown sources, and run on distributed hardware with widely varying configurations and stochastic transient errors. For ...one specific analysis pipeline (RIFT), we have developed a flexible tool (RUNMON-RIFT) to mitigate the most common challenges introduced by uncertainties in source parameters and computational hardware. On the one hand, RUNMON provides mechanisms to adjust pipeline-specific run settings, including prior ranges, to ensure the analysis completes and encompasses the physical source parameters. On the other, it provides tools for identifying and adjusting to the realities of hardware uncertainties. We demonstrate both general features with controlled examples.
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.
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