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Borexino neutrino observatory
Borexino Detector in LNGS in September 2015
Borexino from the North side of LNGS's underground Hall C in September 2015. It is shown close to being completely wrapped in thermal insulation (seen as a silvery wrapping) as an additional effort to further improve its already unprecedented radiopurity levels.
Detector characteristics
Location Laboratori Nazionali del Gran Sasso
Start of data-taking 2007
Detection technique Liquid scintillator (PC+PPO)
Height 16.9 m
Width 18 m
Active mass(volume)

278 tonnes (315 m3)

~100 tonnes fiducial

Borexino is a particle physics experiment to study low energy (sub-MeV) solar neutrinos. The name Borexino is the Italian diminutive of BOREX (Boron solar neutrino experiment, the original experimental proposal with a different scintillator).[1] The experiment is located at the Laboratori Nazionali del Gran Sasso near the town of L'Aquila, Italy, and is supported by an international collaboration with researchers from Italy, the United States, Germany, France, Poland and Russia.[2] The experiment is funded by multiple national agencies including the INFN (National Institute for Nuclear Physics) and the NSF (National Science Foundation). In May 2017, Borexino reached 10 years of continuous operation since the start of its data-taking period in 2007.

The detector is a high-purity liquid scintillator calorimeter. It is placed within a stainless steel sphere which holds the signal detectors (photomultiplier tubes or PMTs) and is shielded by a water tank to protect it against external radiation and tag incoming cosmic muons that manage to penetrate the overburden of the mountain above. The primary aim of the experiment is to make a precise measurement of the individual neutrino fluxes from the Sun and compare them to the Standard solar model predictions. This will allow scientists to test and to further understand the functioning of the Sun (e.g., nuclear fusion processes taking place at the core of the Sun, solar composition, opacities, matter distribution, etc.) and will also help determine properties of neutrino oscillations, including the MSW effect. Specific goals of the experiment are to detect beryllium-7, boron-8, pp, pep and CNO solar neutrinos as well as anti-neutrinos from the Earth and nuclear power plants. The project may also be able to detect neutrinos from supernovae within our galaxy with a special potential to detect the elastic scattering of neutrinos onto protons, due to neutral current interactions. Searches for rare processes and potential unknown particles are also underway. The SOX project will study the possible existence of sterile neutrinos or other anomalous effects in neutrino oscillations at short ranges. Borexino is a member of the Supernova Early Warning System.[3]


As of May 2007, the Borexino detector started taking data.[4] The project first detected solar neutrinos in August 2007. This detection occurred in real-time.[5][6] The data analysis was further extended in 2008.[7]

In 2010, geoneutrinos from Earth's interior have been observed for the first time. These are anti-neutrinos produced in radioactive decays of uranium, thorium, potassium, and rubidium, although only the anti-neutrinos emitted in the 238U232Th chains are visible because of the inverse beta decay reaction channel Borexino is sensitive to.[8][9] Additionally, a multi-source detector calibration campaign took place,[10] where several radioactive sources were inserted in the detector to study its response to known signals which are close to the expected ones to be studied.

In 2011, the experiment published a precision measurement of the beryllium-7 neutrino flux,[11][12] as well as the first evidence for the pep solar neutrinos.[13][14]

In 2012, they published the results of measurements of the speed of CERN Neutrinos to Gran Sasso. The results were consistent with the speed of light.[15] See measurements of neutrino speed. An extensive scintillator purification campaign was also performed, achieving the successful goal of further reducing the residual background radioactivity levels to unprecedented low amounts (up to 15 orders of magnitude under natural background radioactivity levels).

The gray bands compare the regions where the three solar neutrino telescopes, that are able to measure the energy of the events, are sensitive. Note that the predictions of solar models are in logarithmic scale: Super-Kamiokande and SNO can observe about 0.02% of the total, while Borexino may observe each type of predicted neutrino.

In 2013, Borexino set a limit on sterile neutrino parameters.[16] They also extracted a signal of geoneutrinos,[17] which gives insight into radioactive element activity in the earth's crust,[18] a hitherto unclear field.[19]

In 2014, the experimental collaboration published an analysis of the proton–proton fusion activity in the solar core, finding solar activity has been consistently stable on a 105-year scale.[20][21] Once the phenomenon of neutrino oscillations, as described by MSW theory, is considered, the measurement of Borexino is consistent with the expectations from the standard solar model. The result of Borexino is a milestone in our understanding of the functioning of the Sun. It should be noted that the previous experiments sensitive to low energy neutrinos (SAGE, Gallex, GNO) have succeeded to count the neutrinos above a certain energy, but did not measure the individual fluxes.

In 2015, an updated spectral analysis of geoneutrinos was presented,[22] and the world best limit on the electric charge non-conservation (via e→γ+ν decay) was set.[23] Additionally, a versatile Temperature Management and Monitoring System was installed in several phases throughout 2015. It consists of the multi-sensor Latitudinal Temperature Probe System (LTPS), whose testing and first-phase installation occurred in late 2014; and the Thermal Insulation System (TIS), that minimized the thermal influence of the exterior environment on the interior fluids through the extensive insulation of the experiment's external walls. Later in 2015, Borexino also yielded the best available limit to the lifetime of the electron, providing the most stringent confirmation of charge conservation to date.

In 2017, Borexino provided the first wideband spectroscopic measurement of the solar neutrino spectrum, featuring the simultaneous and most precise measurements available of the 7Be, pep and pp neutrino fluxes, furthermore extracted from a single extended energy window (190-2930 keV). These measurements reached a precision of up to 2.7% (in the case of the beryllium solar neutrinos) and established a 5σ confirmation of the presence of pep neutrinos. The limit on the long sought-after CNO neutrinos was kept at the same significance level as in previous Borexino results, which hold the best limit so far, but with weaker assumptions, making the result more robust. Much enlarged statistics thanks to the extra years of exposure, as well as renewed analysis techniques and MonteCarlo state-of-the-art simulations of the whole detector and its physical processes were instrumental in this result. An improvement in the sensitivity to the seasonal modulation of the solar neutrino signal was also reported in 2017. That same year, the best direct-observation limit available for the neutrino magnetic moment was established by Borexino too. A neutrino signal related to the GW150914, GW151226 and GW170104 gravitational wave observations was rejected to within Borexino's sensitivity, as expected.

SOX project[edit]

The SOX experiment[24] aims at the complete confirmation or at a clear disproof of the so-called neutrino anomalies, a set of circumstantial evidences of electron neutrino disappearance observed at LSND, MiniBooNE, with nuclear reactors and with solar neutrino Gallium detectors (GALLEX/GNO, SAGE). If successful, SOX will demonstrate the existence of sterile neutrino components and will open a brand new era in fundamental particle physics and cosmology. A solid signal would mean the discovery of the first particles beyond the Standard Electroweak Model and would have profound implications in our understanding of the Universe and of fundamental particle physics. In case of a negative result, it is able to close a long-standing debate about the reality of the neutrino anomalies, would probe the existence of new physics in low energy neutrino interactions, would provide a measurement of neutrino magnetic moment, Weinberg angle and other basic physical parameters; and would yield a superb energy calibration for Borexino which will be very beneficial for future high-precision solar neutrino measurements.

SOX will use a powerful (~150 kCi) and innovative antineutrino generator made of Ce-144/Pr-144, and possibly a later Cr-51 neutrino generator, which would require a much shorter data-taking campaign. These generators will be located at short distance (8.5 m) from the Borexino detector -under it, in fact: in a pit built ex-profeso before the detector was erected, with the idea it could be used for the insertion of such radioactive sources- and will yield tens of thousands of clean neutrino interactions in the internal volume of the Borexino detector. The experiment is expected to start in 2017 and will take data for about two years.


  1. ^ Georg G. Raffelt (1996). "BOREXINO". Stars As Laboratories for Fundamental Physics: The Astrophysics of Neutrinos, Axions, and Other Weakly Interacting Particles. University of Chicago Press. pp. 393–394. ISBN 0226702723. 
  2. ^ "Borexino Experiment". Borexino Official Website. Gran Sasso. Archived from the original on 16 October 2007. Retrieved 12 August 2011. 
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  18. ^ "Borexino has new results on geoneutrinos". CERN COURIER. Retrieved 20 October 2014. 
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  20. ^ Borexino Collaboration (27 August 2014). "Neutrinos from the primary proton–proton fusion process in the Sun". Nature. 512 (7515): 383–386. Bibcode:2014Natur.512..383B. PMID 25164748. doi:10.1038/nature13702. Retrieved 20 October 2014. 
  21. ^ "Borexino measures the Sun’s energy in real time". CERN COURIER. Retrieved 20 October 2014. 
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External links[edit]

Coordinates: 42°28′N 13°34′E / 42.46°N 13.57°E / 42.46; 13.57