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 Borexino from the North side of LNGS's underground Hall C in September 2015. It is shown close to being completely covered in thermal insulation (seen as a silvery wrapping), providing a relatively cost-effective way to further improve its unprecedented radiopurity levels. | |
| Detector characteristics | |
|---|---|
| Location | Laboratori Nazionali del Gran Sasso |
| Start of data-taking | 2007 |
| End of data-taking | 2021 |
| Detection technique | Elastic scattering on liquid scintillator (PC+PPO) |
| Height | 16.9 m |
| Width | 18 m |
| Active mass(volume) | 278 tonnes (315 m3) ≈100 tonnes fiducial |
Borexino is a deep underground particle physics experiment to study low energy (sub-MeV) solar neutrinos. The detector is the world's most radio-pure liquid scintillator calorimeter and is protected by 3,800 meters of water-equivalent depth (a volume of overhead rock equivalent in shielding power to that depth of water). The scintillator is pseudocumene and PPO which is held in place by a thin nylon sphere. It is placed within a stainless steel sphere which holds the photomultiplier tubes (PMTs) used as signal detectors and is shielded by a water tank to protect it against external radiation. Outward pointing PMT's look for any outward facing light flashes to tag incoming cosmic muons[1] that manage to penetrate the overburden of the mountain above. Neutrino energy can be determined through the number of photoelectrons measured in the PMT's. While the position can be determined by extrapolating the difference in arrival times of photons at PMT's throughout the chamber.[2]
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, opacity, 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. Borexino is a member of the Supernova Early Warning System.[3] Searches for rare processes and potential unknown particles are also underway.
The name Borexino is the Italian diminutive of BOREX (Boron solar neutrino Experiment), after the original 1 kT-fiducial experimental proposal with a different scintillator (TMB), was discontinued because of a shift in focus in physics goals as well as financial constraints.[4] 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, Russia and Ukraine.[5] The experiment is funded by multiple national agencies; the principal ones are INFN (National Institute for Nuclear Physics, Italy) and NSF (National Science Foundation, USA). In May 2017, Borexino reached 10 years of continuous operation since the start of its data-taking period in 2007.
The SOX experiment was a sub-project designed to study the possible existence of sterile neutrinos or other anomalous effects in neutrino oscillations at short ranges through the use of a neutrino generator based on radioactive cerium-144 placed under the water tank of the Borexino detector. This project was cancelled in early 2018 due to the cancellation in 2017 of the contract for cerium-144 by the Russian Mayak fuel reprocessing plant. The cancellation is thought to be connected to the anomalous airborne radioactivity increase in Europe during the autumn of 2017, whose source was eventually localized to the Mayak reprocessing plant.
The entire Borexino experiment was terminated in October 2021.[6]
- ^ Cite error: The named reference
:2was invoked but never defined (see the help page). - ^ Agostini, M.; Altenmüller, K.; Appel, S.; Atroshchenko, V.; Bagdasarian, Z.; Basilico, D.; Bellini, G.; Benziger, J.; Biondi, R.; Bravo, D.; Caccianiga, B.; Calaprice, F.; Caminata, A.; Cavalcante, P.; Chepurnov, A. (November 2020). "Experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun". Nature. 587 (7835): 577–582. arXiv:2006.15115. Bibcode:2020Natur.587..577B. doi:10.1038/s41586-020-2934-0. ISSN 1476-4687. PMID 33239797. S2CID 227174644.
- ^ Borexino Collaboration (2009). "The Borexino detector at the Laboratori Nazionali del Gran Sasso". Nuclear Instruments and Methods in Physics Research Section A. 600 (3): 568–593. arXiv:0806.2400. Bibcode:2009NIMPA.600..568B. doi:10.1016/j.nima.2008.11.076. S2CID 18786899.
- ^ 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 978-0226702728.
- ^ "Borexino Experiment Official Website".
- ^ "About".