The unique manifestation of neutrinos was explained after almost 10 years: why is it so important

Every second, 100 trillion neutrinos pass through the human body.

Particles travel vast distances in space, carrying information about their sources.

Neutrinos are a general name for neutral fundamental particles with half-integer spin that participate only in the weak and gravitational interactions and belong to the class of leptons.Currently, three types of neutrinos are known: electron, muon, and tau neutrinos, as well as their corresponding antiparticles. 

Neutrinos are produced in many processes, such as thermonuclear reactions in the interiors of stars and in supernova explosions.The problem is that these particles are incredibly difficult to detect. to detect them.

Where are neutrinos found?

The construction of the IceCube neutrino observatory at the South Pole was officially completed on December 18 , 2010.It was developed to search for high-energy cosmic neutrinos.of the 5,160 optical sensors — digital optical modules (DOMs) — placed per cubic kilometerAntarctic ice.

How does a neutrino manifest itself?

When a neutrino interacts with an ice molecule,the resulting secondary charged particles emit blue light through a process known as Cherenkov radiation. The light then passes through the ice and may reach some DOMs. As a result, the researchers reconstruct the energy and direction of the particle. This process is based on knowledge of the optical properties of ice. However, once this manifestation of neutrinos greatly surprised scientists.

Cherenkov radiation is a form of energywhich can be observed as a blue glow caused by the charged particles that make up atoms (electrons and protons) moving in a certain environment at speeds exceeding the speed of light.

Unique Phenomenon

In 2013, employees of the IceCube collaborationobserved a unique phenomenon where the observed brightness of the light source depended on the direction of the light. The effect is known as optical anisotropy of ice. Until now, researchers have tried to describe anisotropy using variations in absorption and scattering caused by impurities, but without success.

Anisotropy is the difference in the properties of a medium in differentdirections within this environment; as opposed to isotropy. With respect to some properties, the medium can be isotropic, and with respect to others, anisotropic; the degree of anisotropy may also vary.

In a new study publishedIn The Cryosphere magazine, IceCube staff explained it. It turned out that it appeared as a result of the birefringent properties of elongated ice crystals, which bend light in two directions. In other words, without birefringence, light comes radially from an isotropic light source, and with double refraction, it slowly deviates towards the axis of the ice “flow”.

Illustration showing a newly openedoptical effect: Without birefringence (top), light is emitted radially from an isotropic light source. With birefringence (bottom), light is slowly deflected toward the axis of the ice stream. 
Credit: Jack Pyrin/IceCube Collaboration

This discovery was used to create a newoptical model of ice based on birefringence - SpiceBFR. It is used in detector modeling and has already significantly improved the interpretation of light patterns that result from the interaction of particles in ice.

20 years of research

The optical model of ice that the IceCube collaboration uses has been developed since the early days of the previous AMANDA experiment.

AMANDA Experiment (Antarctic Muon And NeutrinoDetector Array is an Antarctic array of muon and neutrino detectors. In fact, this is a neutrino telescope located under the Amundsen-Scott South Pole Station. In 2005, after nine years of operation, AMANDA officially became part of the successor project, the IceCube neutrino observatory.

For more than 20 years, scientists have added new discoveriesto the known understanding of ice, including the disappearance of trapped air bubbles at depths well above the detector and that at depths, the South Pole Ice Sheet contains the purest ice on the planet.

To improve on previous attempts to describeanisotropy, collaborators carefully studied this effect, discovering its correlation with the deep development of the properties of ice crystals. This led scientists to believe that the many randomly selected small crystals that make up the ice play a role in the observed anisotropy.

What have the scientists done?

To investigate, physicists ran simulations,who modeled the different paths that light could take inside the detector. They then compared the simulated data with a large calibration data set taken from IceCube.

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The IceCube calibration data set containsdata from the 60 000 LEDs that all DOMs are equipped with. These, in turn, emit successive pulses of light into the ice and are then used to calibrate the optical properties of the ice.

What's next and why is it important?

Comparison of indicators helped scientists makeconclusion about the average shape and size of ice crystals inside the IceCube. This exciting new discovery encourages the creation of new simulations and the adaptation of current reconstruction methods to account for the SpiceBFR model.

The discovery will not only help IceCube improvereconstructed neutrino interactions. The research has implications for the field of glaciology as a whole. As the authors of the new work note, the properties of ice crystals are studied, in particular, to understand the mechanics of ice flow. This data can then be used to predict Antarctic mass balance and resulting sea level rise in a changing climate.

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On the cover: Vavilov-Cerenkov radiation in the coolant of the ATR research reactor at the Idaho National Laboratory. Photo: Argonne National Laboratory