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The universe should be a predictably symmetrical locus, according to a cornerstone of Einstein's special theory of relativity, known as Lorentz symmetry. This principle states that any scientist must observe the same laws of physics, in any direction, and regardless of his frame of reference, as long as this object is moving at a constant speed.
For example, due to Lorentz's symmetry, you should observe the same speed of light – 300 million meters per second – if you are an astronaut traveling in space or a molecule moving in the blood.
But for infinitesimal objects that operate at incredibly high energies over vast distances spanning the universe, the same rules of physics may not apply. At these extreme scales, there may be a violation of Lorentz symmetry, or Lorentz violation, in which a mysterious and unknown field distorts the behavior of these objects in a way that Einstein did not predict.
Lorentz violation in various phenomena, from photons to gravity, without definitive results. Physicists believe that if the Lorentz violation exists, it could also be seen in neutrinos, the lightest particles known in the universe, that can travel great distances and are produced by cataclysmic astrophysical phenomena at high levels. energy. Any confirmation that the Lorentz violation exists would reveal a whole new physics that can not be explained by Einstein's theory.
MIT scientists and their colleagues from the IceCube experiment conducted the most comprehensive investigation of the Lorentz violation in neutrinos. They analyzed two years of data collected by the IceCube Neutrino Observatory, a massive neutrino detector buried in the Antarctic ice. The team looked for variations in the normal oscillation of neutrinos that could be caused by a violent Lorentz field. According to their analysis, no anomaly of this type has been observed in the data, which includes the higher energy atmospheric neutrinos collected by any experiment.
The results of the team, published today in Nature Physics rule out possibility of violation of Lorentz in neutrinos in the high-energy range that researchers have analyzed. The results set the strictest limits to date on the existence of Lorentz violation in neutrinos. They also provide evidence that neutrinos behave as predicted Einstein's theory.
"People like the tests of Einstein's theory," says Janet Conrad, professor of physics at MIT and lead author of the paper. "I can not say if people are encouraging him to be right or wrong, but he wins in this one, and it's awesome. To be able to find a theory as versatile as that." he did it is an incredible thing "
Conrad's co-authors at MIT, who also led the search for the Lorentz violation, are postdoc Carlos Argüelles and graduate student Gabriel Collin, who collaborated closely with Teppei Katori, a former postdoc in the Conrad group who is now a lecturer in particle physics at Queen Mary University in London. Their co-authors on paper include the entire IceCube Collaboration, comprising more than 300 researchers from 49 institutions in 12 countries.
Change of Flavor
Neutrinos exist in three main varieties, or as particle physicists I like to call them "flavors": electron, muon and tau. When a neutrino moves in space, its flavor can oscillate or turn into any other aroma. The way neutrinos oscillate usually depends on the mass of a neutrino or the distance it has traveled. But if a Lorentz violating field exists somewhere in the universe, it could interact with the neutrinos crossing that field and affect their oscillations.
To test whether the Lorentz violation can be found in neutrinos, the researchers looked at the data collected by the IceCube Observatory. IceCube is a 1 gigatonne particle detector designed to observe high energy neutrinos produced from the most violent astrophysical sources in the universe. The detector is composed of 5,160 digital optical modules, or light sensors, each of which is attached to vertical ropes that are frozen in 86 boreholes arranged on a cubic kilometer of Antarctic ice.
Neutrinos circulate in space and the Earth can interact with ice that includes the detector or rock below. This interaction produces muon-charged particles that are heavier than electrons. Muons emit light as they pass through the ice, producing long paths that can traverse the entire detector. Based on the recorded light, scientists can follow the trajectory and estimate the energy of a muon, which they can use to recalculate the energy – and the expected oscillation – the original neutrino.
The team, led by Argüelles and Katori, decided to investigate the Lorentz violation in the higher energy neutrinos that are produced in the Earth 's atmosphere.
"Neutrino oscillations are a natural interferometer," says Katori. "The observed neutrino oscillations with IceCube act as the largest interferometer in the world to search for smaller effects such as a spatio-temporal deficit."
The team examined two years of data collected by IceCube, which included more than 35,000 interactions between a muon neutrino and the detector. If a Lorentz violating field exists, the researchers theorized that it should produce an abnormal pattern of oscillations from neutrinos arriving at the detector of a particular direction, which should become more relevant as the the energy increases. Such an abnormal oscillation pattern should correspond to an abnormally similar energy spectrum for muons.
The researchers calculated the gap in the energy spectrum that they would expect to see if the Lorentz violation existed, and compared that spectrum to the actual energy spectrum. observed, for the most energetic neutrinos in the atmosphere.
"We are looking for a deficit of muon neutrinos along the direction that crosses large portions of the Earth," says Argüelles. "This disappearance-induced violation of Lorentz is expected to increase with the increase of energy."
If the Lorentz violation exists, physicists believe that it should have a more obvious effect on objects at extremely high energies. The atmospheric neutrino dataset analyzed by the team is that of the most energetic neutrinos collected by an experiment.
"We were trying to find out if a violation of Lorentz caused a deviation, and we did not see it." "This closes the book on the possibility of Lorentz violation for a series of high-energy neutrinos, for a very long time."
A Limit of Violation
The team's findings set the toughest limit yet on how neutrinos can be affected by a violent Lorentz field. The researchers calculated, based on IceCube data, that a violating field with an associated energy greater than 10-36 GeV-2 should not affect the oscillations of a neutrino. Let .01 with 35 other zeros preceding the 1, one-billionth a square electronvolt – an extremely weak force that is much weaker than the normally weak interactions of neutrinos with the rest of the matter, which is at the level of 10-5 GeV -2-
"We have been able to set limits to this hypothetical domain that are much, much better than those that have been produced before," says Conrad. "It was an attempt to go out and look at a new territory that we had not looked at before and see if there are any problems in this space, and there are not, but that does not stop us from going further. " 19659002] At this stage, the group plans to investigate the Lorentz violation in even more energetic neutrinos produced from astrophysical sources. IceCube records astrophysical neutrinos, as well as atmospheric neutrinos, but scientists do not have a complete understanding of their behavior, such as their normal oscillations. Once they can better model these interactions, Conrad says that the team will have a better chance of looking for models that deviate from the norm.
"Every article that comes out of particle physics assumes that Einstein is right, and all the rest our work relies on that," says Conrad. "And at a very good approximation, he has reason, it's a fundamental structure of our theory, so trying to understand where there are deviations is a very important thing to do. "
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