The great neutrino mystery may point to missing particles

In 1993, the deep In the underground of Los Alamos National Laboratory in New Mexico, a few flashes in a bus-sized fuel tank opened up an unconclusive detective story.

The Liquid Scintillator Neutrino Detector (LSND) is looking for radiation bursts produced by neutrinos, which are the lightest and most elusive of all known elementary particles. “To our surprise, this is what we saw,” said Bill Louis, one of the leaders of the experiment.

The issue is They see too muchTheorists hypothesize that neutrinos may oscillate between different types during flight—a hypothesis that explains various astronomical observations. LSND has set out to test this idea by aiming a beam of mu neutrinos (one of three known types) at the fuel tank and counting the number of electron neutrinos that arrive there. However, Lewis and his team detected more electron neutrinos than the simple neutrino oscillation theory predicted.

Since then, dozens of neutrino experiments have been established, each of which is more ambitious than the previous one. In the mountains, abandoned mining caves and the ice below Antarctica, physicists built cathedrals for these notorious slippery particles. But when these experiments detect neutrinos from all angles, they continue to produce conflicting pictures of particle behavior. “The plot keeps getting deeper,” Louis said.

“This is a very confusing story. I call it the Fork Road Garden,” said Carlos Aguiles-Delgado, A neutrino physicist at Harvard University. In the 1941 short story of Jorge Luis Borges, time branches into countless possible futures. For neutrinos, conflicting results have led theorists on various paths, unsure of which data is trustworthy and which might lead them astray. Argüelles-Delgado said: “Like any detective story, sometimes you will see clues, but they will push you in the wrong direction.”

In 1993, the liquid scintillator neutrino detector at Los Alamos National Laboratory reported a large number of puzzling neutrino detections. Engineer Rick Bolton kneels between the photomultiplier tubes. Once filled with mineral oil, these photomultiplier tubes will detect light from the interaction of neutrinos in the tank.Provided by Los Alamos National Laboratory

The simplest explanation for the LSND anomaly is the existence of a new fourth type of neutrino, called an inert neutrino, which mixes all types of neutrinos according to the new rules. Sterile neutrinos will make it easier for meson neutrinos to oscillate into electron neutrinos within a short distance from the fuel tank.

But over time, sterile neutrinos did not match the results of other experiments. “We have our championship theory, but the problem is that it failed miserably elsewhere,” Argüelles-Delgado said. “We are deep in the forest, we need to come out.”

The physicists were forced to go back the same way, and have been rethinking what is behind the messy prompts and halfway. In recent years, they have devised new theories that are more complex than inert neutrinos, but if these theories are correct, they will revolutionize physics—at the same time solving anomalies in neutrino oscillation data and other major physics mysteries. More importantly, the new model assumes that a large number of extra neutrinos can explain dark matter. These invisible things envelop galaxies and seem to be four times larger than normal matter.

now, Four analyses released yesterday by the MicroBooNE experiment Fermi National Accelerator Laboratory near Chicago and Another recent study of the IceCube detector Both experiments in Antarctica indicate that these more complex neutrino theories may be on the right track-although the future is still very uncertain.

“I feel as if something is floating in the air,” Argüelles-Delgado said. “This is a very stressful environment, pointing towards discovery.”

Desperate remedy

When Wolfgang Pauli hypothesized in 1930 that there were neutrinos to explain where the energy disappeared during radioactive decay, he called it a “desperate remedy.” His theoretical structure has no mass or charge, which makes him doubt whether experiments can detect it. “This is something no theorist should do,” he wrote in his diary at the time. But in 1956, in an experiment different from LSND, There are neutrinos.

When physicists detected neutrinos from the sun (the natural source of particles) and found that the number of neutrinos was less than half of what the theoretical model of stellar nuclear reaction predicted, Triumph quickly fell into chaos. By the 1990s, it became clear that neutrinos behaved strangely. Not only did the sun’s neutrinos seem to mysteriously disappear, but the neutrinos that fell on the earth when cosmic rays collided with the upper atmosphere also mysteriously disappeared.

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