For decades, physicists have hypothesized that the current best theory describing particle physics – the “Standard Model” – was not sufficient to explain how the universe works. In the search for physics beyond the Standard Model (BSM), elusive particles called neutrinos could lead the way.
Neutrinos are sometimes referred to as “ghost particles” because they so rarely interact with matter that they can pass through just about anything. However, as they travel through matter, they can be “slowed down”, depending on the type (or “flavor”) of the neutrino, in what is called a “matter effect”.
In many BSM models, neutrinos have additional interactions with matter due to new and heretofore unknown forces of nature. Different flavors of neutrinos can be affected to varying degrees by these interactions, and the strength of the resulting matter effects depends on the density of matter through which the neutrinos pass. If the researchers observe material effects that can be explained as “non-standard interactions” (NSI), it could point to new physics.
The IceCube Neutrino Observatory, a set of sensors embedded in the ice at the South Pole, was built to detect and study neutrinos from space. But at the center of IceCube is a subset of denser sensors called DeepCore; this region is sensitive to lower energy neutrinos formed in the Earth’s atmosphere which are potentially more strongly affected by the effects of non-standard matter. In an article published today in Physical examination D, the IceCube collaboration discusses an analysis in which they looked at three years of DeepCore data to see if atmospheric neutrinos have additional interactions with matter. This analysis places limits on all of the parameters used to describe NSI, an improvement over previous analyzes which were limited to only NSI regimes to which IceCube is most sensitive.
Valuable ambassadors of new physics
“Atmospheric neutrinos are an excellent probe for testing whether neutrinos have an NSI as they pass through the Earth, including its center, which has a very high density of matter,” says Elisa Lohfink, a graduate student at the University of Mainz in Germany and leader on this issue. Changes in matter density directly alter neutrino oscillation patterns – the way neutrinos change their flavor, or “oscillate” – and therefore what flavors of neutrinos arrive at the South Pole detector. IceCube DeepCore is sensitive to these matter effects due to the large number of atmospheric neutrinos it detects each year.
In this analysis, led by Thomas Ehrhardt, a graduate student at the University of Mainz, the researchers examined the oscillation patterns of the neutrinos that had arrived at DeepCore from all directions and determined whether they met the expectations of the Standard Model. or showed effects of one of the five effective parameters that measure how much a neutrino flavor interacts more than in the Standard Model. The researchers could then constrain the actual NSI parameters by testing how well the oscillation model fits different NSI scenarios.
First, Ehrhardt and coworkers looked at one effective parameter at a time, yielding the results shown in the figure above. Completely free INS were studied separately. Since the analysis was largely independent of any specific underlying model, the researchers were able to coerce NSI without relying on a model to be correct.
The researchers were able to individually set limits on each of the five possible NSI parameters at a sensitivity at least comparable to the combined limits of the world, an achievement described by Lohfink as “unprecedented”. More importantly, according to the researchers, the discovery that IceCube can probe patterns in which they match all parameters at once. “To our knowledge, no other experiment in the world can do this from a single measurement,” says Sebastian Böser, professor at the University of Mainz. “We can put limits on an unprecedented range of models for new physics in the neutrino sector.” The result is a major improvement over a previous IceCube analysis which looked at just one parameter.
The researchers hope the rest of the neutrino community will take up the results and incorporate them into the overall fits. And Lohfink and coworkers are already working on a follow-up analysis using a much larger data sample (eight years of data instead of three years) with much better sensitivity. They hope to have an improved limit soon.
“In the long term, the IceCube upgrade will be a real game-changer for this type of analysis,” says Böser. “Not only will the upgrade provide better calibration and reduce the impact of systematic uncertainties, it will also allow us to solve neutrino oscillations much, much better, and therefore allow us to see potential deviations from them much more clearly. to the standard model. I’m really excited about this! ”
In search of dark matter inside the Earth
R. Abbasi et al, All-flavor constraints on non-standard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data, Physical examination D (2021). DOI: 10.1103 / PhysRevD.104.072006
Provided by Universitaet Mainz
Quote: Analysis puts most general constraints on nonstandard neutrino interactions (2021, October 18) retrieved October 20, 2021 from https://phys.org/news/2021-10-analysis-constraints-nonstandard-neutrino -interactions.html
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