Idea of ​​a mysterious fourth neutrino supported by new experiments

Image Credit: Barbol/

Image Credit: Barbol/

An anomaly previously observed in experiments has been confirmed by new work, adding to evidence that something is wrong with the Standard Model of particle physics. The work can give an idea of ​​what exactly is wrong.

The results come from an experiment looking for the hypothetical sterile neutrino: a fourth electrically neutral, low-mass particle believed to exist above the standard three neutrinos we know exist.

As reported in the magazines Physical Assessment Letters and Physical assessment C, the experiment confirms the earlier findings. The setup is made of irradiated chromium-51 disks (which do not form naturally), a major source of electron neutrinos. The disks are in two tanks made of gallium, and the electron neutrino bombardment turns some of the gallium atoms into germanium-71 atoms.

However, the measured rate of this reaction is between 20 and 24 percent lower than the theoretical modeling. One possibility for this shortage of electron neutrinos is that there is a fourth neutrino known as a sterile neutrino. Otherwise the theory is wrong.

“The results are very exciting,” said Steve Elliott, chief analyst for one of the teams that reviewed the data and a member of the Los Alamos physics division. pronunciation† “This definitely confirms the anomaly we’ve seen in previous experiments. But what this means is not clear. There are conflicting results now about sterile neutrinos. If the results show that fundamental nuclear or atomic physics is being misunderstood, so would be.” be very interesting.”

Neutrinos come in three flavors – a surprising technical term that has nothing to do with the sense of taste. There are electron neutrinos, muon neutrinos and tau neutrinos. One of the most fascinating aspects of neutrinos is that they oscillate, meaning they change from one flavor to another as they move through the universe.

They can move for a very long time. Having such a small mass and being electrically neutral means they interact very little. Every second 100 trillion neutrinos pass through your body as if you weren’t even there.

The Soviet-American Gallium Experiment (SAGE), which started in the late 1980s, pointed to a possible shortage of electron neutrinos. The Baksan Experiment on Sterile Transitions (BEST), the results of which we discuss here, confirms this.

One possibility is that the electron neutrino oscillates in a sterile neutrino, which could explain the reduced production of germanium. Alternatively, the electron neutrino cross section — the probability that a specific particle interaction would occur — might not be what the theory says it is.

The Standard Model of particle physics is one of the best sets of ideas ever created by mankind, allowing us to predict particles long before they were discovered, such as the Higgs boson. But it’s also limited, and physicists are now reaching those limits in hopes of revealing what lies beyond.

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