In 1993, worm underground at the Los Alamos National Laboratory in New Mexico, a few flashes of light inside a bus-sized tank of oil set off a detective story that has yet to be concluded.
The Liquid Scintillator Neutrino Detector (LSND) is looking for bursts of radiation produced by neutrinos, the lightest and most elusive of all known elementary particles. “We were surprised, that’s what we saw,” said Bill Louis, one of the people who led the trial.
The problem is they have seen too much. Theorists have recognized that neutrinos can oscillate between types as they fly along – a hypothesis that explains different astronomical observations. The LSND began testing this idea by directing a beam of muon neutrinos, one of three known, at the oil barrel, and counting the number of electron neutrinos that got there. However, Louis and his team detected far more incoming electron neutrinos in the pool than the simple theory of neutrino oscillations had predicted.
Since then, dozens of other neutrino experiments have been built, each more epic than the last. In the mountains, unused mining caves, and the ice beneath Antarctica, physicists have erected sanctuaries for these famous slippery particles. But as these experiments probed neutrinos from all angles, they repeatedly presented conflicting pictures of how particles behave. “The plot just kept thickening,” Louis said.
“It is a very confusing story. I call it the Garden of Forking Roads,” Carlos Argüelles-Delgado, a neutrino physicist at Harvard University. In Jorge Luis Borges’ 1941 short story of that title, time branches into an infinite number of possible futures. With neutrinos, conflicting results have led theorists along different paths, unsure of which data to trust and which might lead them astray. “Like any detective story, sometimes you see clues and they throw you in the wrong direction,” says Argüelles-Delgado.
The simplest explanation for the LSND anomaly is the existence of a new fourth type of neutrino, called a sterile neutrino, which mixes all types of neutrinos according to new rules. Sterile neutrinos will allow muon neutrinos to more easily oscillate into electronic neutrinos over short distances from the barrel of oil.
But as time went on, the sterile neutrino did not match the results of other experiments. “We had our championship theory, but the problem is that elsewhere it failed miserably,” said Argüelles-Delgado. “We were very deep in the forest, and we needed to get out.”
Forced to retrace their steps, physicists have been rethinking what lies behind the mess of hints and half-results. In recent years, they have devised new theories that are more complex than sterile neutrinos, but if true, would completely revolutionize physics — while also addressing anomalies in neutrino oscillation data and other great mysteries of physics. Equally important, the new models pose additional heavy neutrinos that could make up the dark matter, the invisible stuff that surrounds galaxies that appear to be four times more abundant than normal matter.
Now, four analytics released yesterday by MicroBooNE . test at the Fermi National Accelerator Laboratory near Chicago and another recent study from the IceCube detector at the South Pole, both suggest that these more complex neutrino theories may be on the right track — though the future remains unclear.
Argüelles-Delgado said: “I felt like something was floating in the air. “It’s a very stressful environment geared toward discovery.”
A desperate remedy
When Wolfgang Pauli recognized the existence of neutrinos in 1930 to explain where energy disappears during radioactive decay, he called it a “desperate cure”. His theoretical structure had no mass or charge, making him doubtful that an experiment could detect it. “That is something no theorist should do,” he wrote in his diary at the time. But in 1956, in an experiment no different from LSND, where the neutrino is.
Triumph soon became confused when physicists discovered neutrinos coming from the sun, a natural source of particles, and found less than half the number predicted by theoretical models of particle reactions. multiplier of stars. In the 1990s, it became clear that neutrinos were behaving strangely. Not only do solar neutrinos seem to mysteriously disappear, but neutrinos fall to Earth as cosmic rays collide with the upper atmosphere.
