Scientists prove a decades-old theory that could change particle physics

Neutrinos are among the most mysterious particles that exist. They are extremely difficult to detect because they tend to avoid other particles, but we know that they are expelled by supernovae, that one hundred trillion pass through our bodies every second at almost the speed of light, and that they could be similar to dark matter.

Now we know a little more: Scientists at the Department of Energy’s Oak Ridge National Laboratory have just proven a decades-old theory about neutrinos that has huge implications for astrophysics and even the “model.” standard” of particle physics.

Until now, we could only find neutrinos by tracking their interactions with protons. Such a collision causes the proton to decay into a neutron and an electron and this electron creates a small measurable flash of light.

We now have a new method of detection – although in a way it’s not new at all, as physicist Daniel Freedman theorized about it in a 1974 paper. He suspects that neutrinos interact with atomic nuclei as well as with protons. Forty years later, Freedman was finally right.

The Oak Ridge lab used a machine called the Spallation Neutron Source (SNS) to shoot neutrons onto a beamline, a process that creates neutrinos as a byproduct. They placed the SNS in front of a 20-foot-thick concrete wall that would block most particles but let neutrinos through.

“Because SNS produces pulsed neutron beams, the neutrinos are also pulsed, allowing easy separation of the signal from the background noise,” reads the press release. Physicists used these pulses to detect neutrinos hitting atomic nuclei, just as Freedman had postulated.

This tactic for finding neutrinos is much better than the old one: the chances of neutrinos interacting with nuclei are 100 times greater than the chances of them interacting with protons, simply because nuclei are much larger than protons.

What is the meaning of all this? This means that physicists can create neutrino detectors that are a a lot smaller and portable size. This – along with the fact that we now know that neutrinos can, indeed, interact with nuclei – has even bigger implications. In fact, we have just taken a major step towards a better understanding of supernovae and finally the identification of dark matter.

Dark matter is even harder to detect than neutrinos (so much so that we still don’t know what it is). Some scientists believe that dark matter particles are actually quite similar to neutrinos: that they also interact with nuclei and could be found by observing the reactions of these nuclei. If so, physicists will need to find a way to filter out the signals from neutrinos colliding with nuclei in order to focus on dark matter collisions. “Yesterday’s signal becomes today’s background,” said physicist Hirohisa Tanaka. WIRED. Now that scientists know more about neutrinos, they have a better idea of ​​what to filter out.

Supernovae – the expanding balls of gas that erupt when massive stars explode – are better understood than dark matter, but they remain enigmatic. Astronomers have modeled the ways these events can begin and unfold; more information about neutrinos will help corroborate or disprove these models, since 99% of supernova energy is emitted as neutrinos.

“When a massive star collapses and then explodes, neutrinos pour great energy into the stellar envelope,” COHERENT spokeswoman Kate Scholberg said in the press release. “Understanding the process helps to understand how these dramatic events happen.”

This new method of detecting neutrinos could even help scientists solve some of the problems of the so-called “standard model” of particle physics. The model seems to fit most phenomena, but physicists have found that it doesn’t quite fit neutrinos; according to the model, neutrinos should not have mass, but they do. Now that there’s a simpler, smaller, and lighter way to detect neutrinos, physicists might finally be able to figure out what’s wrong with the model.

As if all that weren’t enough, scientists could use this new method “to better understand the structure of the nucleus,” Scholberg said in the press release.

The implications are so vast that they are even difficult to comprehend, but we will see them play out in the years to come as physicists learn even more about neutrinos and use them to unlock the mysteries of our world and the planet. outer space.

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