hard · LSAT Reading Comprehension
For decades, the standard model of particle physics held that neutrinos—tiny, nearly massless particles produced in nuclear reactions—had no mass at all. However, this model was challenged by the 'solar neutrino problem': detectors on Earth were recording only a fraction of the neutrinos predicted to be coming from the sun. The solution came with the discovery of neutrino oscillations. Neutrinos exist in three types, or 'flavors.' As they travel through space, they can spontaneously transform from one flavor into another. Because the early detectors were only sensitive to one flavor, they were missing the neutrinos that had switched during their journey. For this oscillation to occur, quantum mechanics requires that neutrinos must possess a non-zero mass. This discovery forced a significant revision of the standard model and opened new questions about the nature of dark matter, as neutrinos' mass, though tiny, could have significant gravitational effects across the universe.
Which one of the following, if true, would most seriously weaken the explanation that neutrino oscillation is the cause of the solar neutrino problem?
- Detectors built to register all three flavors at once still tally far fewer neutrinos than the sun is predicted to emit.
- Neutrinos from non-solar sources, such as nearby nuclear reactors, also reliably display flavor-to-flavor oscillation.
- Updated solar models now predict the sun emits even more neutrinos than thought, widening the gap with the early single-flavor counts.
- The neutrino's rest mass has turned out to be even smaller than the current lower-bound estimates, yet remains firmly above zero.
- Neutrino oscillation has been formally shown to be physically impossible under every known version of quantum mechanics.
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