Scientists Just Spotted a 1-In-10-Billion Quantum Physics Phenomenon
When protons smash against a beryllium target in CERN’s Super Proton Synchrotron (SPS), the resulting subatomic chaos produces a smattering of kaons—a kind of subatomic particle.
Physicists predict that from these kaons, roughly one in 10 billion will decay into a positively-charged pion a neutrino/antineutrino pair. And now, they’ve successfully detected it.
This particular decay is a ripe candidate for discovering entirely new particle physics.
Quarks are quirky. The building blocks of all matter, these subatomic particles have a tendency to completely reform into different things when subjected to incredible collisions in a particle accelerator. Roughly six percent of the time, that recombination will result in a kaon, a different kind of subatomic particle.
This is where things begin to get strange. Roughly one out of 10 billion times, a positively-charged kaon decays into a positively-charged pion and a neutrino-antineutrino pair. Even though nearly one billion secondary particles are produced each second of these experiments, it takes a significant amount of time to find the lone exception to what appears to be a rule of our current understanding of the Standard Model of Physics. Now, physicists who are part of the NA62 collaboration—a group dedicated to studying rare kaon decays—has announced at a CERN seminar that their team successfully documented this “ultra rare particle decay.”
“This observation is the culmination of a project that started more than a decade ago,” Giuseppe Ruggiero, a researcher with NA62, said in a press statement. “Looking for effects in nature that have probabilities of happening of the order of 10-11 is both fascinating and challenging. After rigorous and painstaking work, we have finally seen the process NA62 was designed and built to observe.”
To make these kaons, you need some seriously specialized equipment. In particular, you need the Super Proton Synchrotron (SPS)—the second largest machine in the CERN accelerator complex (second only to the Large Hadron Collider, of course). The SPS fires a stream of high-energy protons at a beryllium target, producing a secondary beam that is just six percent kaons. The particles enter a vacuum tank where a silicon-pixel detector measures the resulting subatomic chaos.
Studying kaons—and, in particular, these specific decay behaviors—is critical to our understanding of physics because they are “extremely sensitive to deviations from the Standard Model prediction,” according to the researchers. This makes kaon to pion-and-neutrino-antineutrino decay one of the few areas in which new particle physics could be discovered. Although the researchers say that their results are 50 percent larger than the Standard Model predicts, the measurements are potentially accurate, as they are in the realm of uncertainty.
“Searching for hints of new physics in this decay requires more data, but this result is a leap forward and further strengthens the strong interest in this line of research,” Karim Massri, NA62 physics coordinator, said in a press statement.
This pion-neutrino pair decay has been predicted by the Standard Model and has even technically been detected before, but this is the first time the team measured the event with a statistical significance of just five standard deviations (measured in sigma). The higher the sigma, the less likely the detection is to be a fluke or glitch and the more likely the hypothesis is true. Crossing the five sigma threshold usually denotes a discovery—the detection of the Higgs boson, for example, was only announced when a reading had been captured with a statistical significance beyond five sigma.
Now that the physicists have confirmed this event, and the confirmation was deemed statistically significant, they can now push forward and study the unknown attributes of this ultra-rare event.
“This measurement relies on identifying the one-in-10-billion K+ decay that is our signal and making sure it is not one of the other 9,999,999,999 decays that can mimic the signal,” Joel Swallow, lead data analyst on the project, said in a press statement. “The whole NA62 collaboration has made this almost impossible result possible.”
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