In the 1990s, an experiment to study neutrinos found some strange phenomena: too many particles appeared in the detector. In 2002, scientists began another experiment to find out what happened. The experiment also obtained surprising results in another way. Then a third test was conducted in 2015. The measurement results released last week did not solve these two puzzles, but deepened the mystery.
These projects all focus on neutrinos, the most abundant particles in nature, except photons (light particles). These tiny, uncharged particles flow out of the sun like supernovae and other cosmic events, and about one trillion particles pass through your hand every second. They are known to have three types, or three flavors: electron neutrinos μ Neutrino sum τ Neutrinos. But many scientists hope that a fourth type of “sterile neutrino” will appear. If neutrinos exist, sterile neutrinos may help solve several mysteries in physics. For example, the theory predicts that neutrinos should not have mass, but why neutrinos have mass, and what is the composition of invisible dark matter all over the universe. The puzzling excess particles in early experiments excited researchers because they looked like possible signs that sterile neutrinos interfered with the taste of normal neutrinos.
This hypothetical neutrino is called “sterile” neutrino because they can only interact with other particles through gravity, and the three known neutrinos can also interact through weak forces. But they may affect other neutrinos, because these particles have a strange characteristic: they can “oscillate” or change their taste. For example, a particle starting with an electron neutrino can be transformed into τ or μ Neutrinos, and vice versa. Usually, this transition occurs when neutrinos move a certain distance, but it seems to occur faster in the liquid scintillation neutrino detector (LSND) at Los Alamos National Laboratory and its subsequent experiment, the miniboone booster neutrino experiment at Fermilab, in badavia, Illinois. Scientists believe that, μ Neutrinos may oscillate into sterile neutrinos, and then oscillate into electronic neutrinos. This process may be simpler than that μ Sub to electronic flavor switches occur faster.
The latest findings come from mini animal experiments carried out by Minnie Boone’s successor at Fermilab. The physicists there had a wave μ Meson neutrino streams and shoot them at the detector 470 meters away. The detector is a huge container filled with 170 metric tons of pure liquid argon, waiting to catch neutrinos hitting the nucleus of one of the argon atoms. Such collisions are very rare, and their only sign is the secondary particles produced by the interaction.
On October 27, scientists announced the results of microboone, saying they did not see the excess observed by microboone. “Yes, it’s a little strange,” said Bonnie Fleming, a co spokesman for Yale’s microblog. Early experiments saw additional particles that looked like electrons or photons, although they could not confirm both possibilities. However, the micro detector can more accurately observe the moving direction of particles in the detector and the energy they deposit. “This means that we can tell whether an object is an electron or a photon,” Fleming said. “A real victory of this experiment is that this technology works very well.” however, the result is that microsatellite scientists are very sure that there are no redundant electrons or photons everywhere they observe, thus eliminating the hope of some sterile neutrinos. if μ Meson neutrinos can be quickly transformed into sterile neutrinos, and then into electron neutrinos, then electrons will appear in micro pool. (the detector is not far from its source, ordinary μ Meson neutrino to electron neutrino oscillations do not occur.)
But if there are no extra electrons or photons, what are the extra particles seen by LSND and miniboone? One option is that in the early two experiments, unexplained neutrino collisions actually did not occur, while in the miniboone example, the researchers just missed some interference inside the experimental detector. “Maybe some aspects of the detector are not completely clear,” said Joachim Kopp, a theoretical physicist at CERN, the European particle physics laboratory near Geneva and Johannes Gutenberg University Mainz in Mainz, Germany. “But I don’t think these highly skilled people are likely to do that.”
Others agree. “The detector is unlikely to have some calibration errors,” said Andr é de gouv ê a, a theoretical physicist at Northwestern University. “There must be a new source of electrons or photons, or something that looks like electrons or photons,” he said. Maybe something more complex is happening. provide μ Neutrino neutrino sources can also produce heavier sterile neutrinos or other new particles rather than μ Neutrinos oscillate into sterile neutrinos, and then oscillate into electronic neutrinos. These particles may decay into other things, such as an ordinary neutrino and some strange things, such as “dark photon” (a close relative of an ordinary photon that has been theorized but never found). If this process happens, it will produce an electron and its antimatter partner, a positron, which will appear in a different signal than ordinary electrons. Miniature animals have not yet found such a pair.
Sterile neutrinos remain an attractive prospect for physicists. They are probably a by-product of the theory of trying to explain why neutrinos have mass. They can also help explain what dark matter is. Some kinds of sterile neutrinos may be candidates for dark matter itself, or they may be part of the “dark area” where dark matter particles are related to sterile neutrinos or decay into sterile neutrinos. “If you (among physicists) ask around and say, ‘do you think there are sterile neutrinos?’ I think everyone will say it’s possible,” de gouv ê a said. “But the devil lies in the details. Is it heavy or light, easy to see or difficult to see?”
Figuring out what happened in these neutrino experiments may be the first step to answer these larger questions. “It’s really interesting because all the obvious possibilities have been tested now,” Kop said. “The good news is that we have tools to further investigate this problem and hope to find the root cause of the problem.”
What Lies Ahead
The micro cell is part of a larger neutrino project at Fermilab, called the short baseline neutrino (SBN) project, which includes three liquid argon neutrino detectors with different distances from the neutrino source. The other two detectors are short baseline near detector (sbnd) only 110m away from the source and Icarus T600 detector further 600m away. In the middle of 470 meters, micro ketones begin to collect data. Icarus and sbnd will start this year and 2023 respectively.
“The plan aims to make a more inclusive measurement and find possible areas to allow parameters in a more global way,” said Ornella palamara of Fermilab, a co spokesman for sbnd. For example, if the correct explanation for the miniboone result is sterile neutrinos, scientists will see them on the far detector in addition to the emergence of electronic neutrinos μ The corresponding disappearance of the neutrino event because the particles move farther from the neutrino source. “This is the advantage of the SBN multi detector program, which cannot be achieved by a single detector,” palamara said. “We can do a lot of things. These analysis from microblog is just the beginning.”
Scientists say that the recent maturity of microbial analysis technology heralds the future. Marcela carena, head of Fermilab’s theory department, said: “this is very exciting because microsatellites have achieved an unprecedented level of knowledge in understanding these neutrino events.”. “This will enable future experiments to facilitate their physical search.”
So far, the conclusion on sterile neutrinos is still inconclusive. “I don’t think the idea of sterile neutrinos is dead,” Karena said. “The search for sterile neutrinos continues.”