Solar neutrino problem
The solar neutrino problem concerned a large discrepancy between the flux of solar neutrinos as predicted from the Sun's luminosity and as measured directly. The discrepancy was first observed in the mid-1960s and was resolved around 2002.
The flux of
Particle physicists knew that a mechanism, discussed back in 1957 by
Several neutrino detectors aiming at different flavors, energies, and traveled distance contributed to our present knowledge of neutrinos. In 2002 and 2015, a total of four researchers related to some of these detectors were awarded the Nobel Prize in Physics.
Background
The Sun performs
In the late 1960s,
The expected number of solar neutrinos was computed using the standard solar model, which Bahcall had helped establish. The model gives a detailed account of the Sun's internal operation.
In 2002, Ray Davis and Masatoshi Koshiba won part of the Nobel Prize in Physics for experimental work which found the number of solar neutrinos to be around a third of the number predicted by the standard solar model.[2]
In recognition of the firm evidence provided by the 1998 and 2001 experiments "for neutrino oscillation",
Proposed solutions
Early attempts to explain the discrepancy proposed that the models of the Sun were wrong, i.e. the temperature and pressure in the interior of the Sun were substantially different from what was believed. For example, since neutrinos measure the amount of current nuclear fusion, it was suggested that the nuclear processes in the core of the Sun might have temporarily shut down. Since it takes thousands of years for heat energy to move from the core to the surface of the Sun, this would not immediately be apparent.
Advances in
Resolution
The solar neutrino problem was resolved with an improved understanding of the properties of neutrinos. According to the Standard Model of particle physics, there are three flavors of neutrinos: electron neutrinos, muon neutrinos, and tau neutrinos. Electron neutrinos are the ones produced in the Sun and the ones detected by the above-mentioned experiments, in particular the chlorine-detector Homestake Mine experiment.
Through the 1970s, it was widely believed that neutrinos were massless and their flavors were invariant. However, in 1968 Pontecorvo proposed that if neutrinos had mass, then they could change from one flavor to another.[8] Thus, the "missing" solar neutrinos could be electron neutrinos which changed into other flavors along the way to Earth, rendering them invisible to the detectors in the Homestake Mine and contemporary neutrino observatories.
The
Strong evidence for neutrino oscillation came in 1998 from the Super-Kamiokande collaboration in Japan.[10] It produced observations consistent with muon neutrinos (produced in the upper atmosphere by cosmic rays) changing into tau neutrinos within the Earth: Fewer atmospheric neutrinos were detected coming through the Earth than coming directly from above the detector. These observations only concerned muon neutrinos. No tau neutrinos were observed at Super-Kamiokande. The result made it, however, more plausible that the deficit in the electron-flavor neutrinos observed in the (relatively low-energy) Homestake experiment has also to do with neutrino mass.
One year later, the
References
- ISSN 1687-7357.
- ^ "The Nobel Prize in Physics 2002". Retrieved 2020-02-16.
- ^ "The Nobel Prize in Physics 2015". Retrieved 2020-02-16.
- ^ Webb, Jonathan (6 October 2015). "Neutrino 'flip' wins physics Nobel Prize". BBC News. Retrieved 6 October 2015.
- arXiv:1609.02386.
- ^ Adrian Cho: "Did the Nobel committee get the physics wrong?" Science, December 14, 2016, doi:10.1126/science.aal0508.
- ^ Haxton, W.C. Annual Review of Astronomy and Astrophysics, vol 33, pp. 459–504, 1995.
- .
- ^
W. David Arnett & Jonathan L. Rosner (1987). "Neutrino mass limits from SN1987A". PMID 10034569.
- ^ Edward Kearns, Takaaki Kajita, and Yoji Totsuka: "Detecting Massive Neutrinos". Scientific American, August 1999.
- ^ H.H. Chen, "Direct Approach to Resolve the Solar Neutrino Problem," Physical Review Letters 55, 1985, doi:10.1103/PhysRevLett.55.1534.
- ^ Q.R. Ahmad, et al., "Measurement of the Rate of Interactions νe + d → p + p + e− Produced by 8B Solar Neutrinos at the Sudbury Neutrino Observatory," Physical Review Letters 87, 2001, doi:10.1103/PhysRevLett.87.071301.
- arXiv:1602.02469.
External links
- Solar neutrino data
- Solving the Mystery of the Missing Neutrinos
- Raymond Davis Jr.'s logbook Archived 2006-10-02 at the Wayback Machine
- Nova – The Ghost Particle
- The Solar Neutrino Problem by John N. Bahcall
- The Solar Neutrino Problem, by L. Stockman
- A set of photos of different Neutrino detectors
- John Bahcall's web site