![Illustration visualizing the newly discovered optical effect: without birefringence (top), light flows radially from an isotropic light source. With birefringence (bottom), light is slowly bent towards the axis of the ice flow. Credit: Jack Pairin / IceCube Collaboration A team of scientists from Mainz manages to see through the diffuse ice of Antarctica](https://oponame.com/wp-content/uploads/2022/10/Newly-Discovered-Optical-Effect-Allows-IceCube-Neutrino-Observatory-to-Infer.jpg)
Illustration visualizing the newly discovered optical effect: without birefringence (top), light flows radially from an isotropic light source. With birefringence (bottom), light is slowly bent towards the axis of the ice flow. Credit: Jack Pairin / IceCube Collaboration
Every second, 100,000 billion neutrinos pass through the human body. These tiny, nearly massless particles travel enormous distances through space while carrying information about their sources and are created by some of the most energetic phenomena in the universe. But neutrinos are incredibly difficult to detect, requiring a one-of-a-kind detector that can “see” these nearly invisible particles.
On December 18, 2010, the IceCube neutrino observatory, located at the South Pole, was completed. Designed to search for high-energy cosmic neutrinos, the detector consists of an array of 5,160 optical sensors, called digital optical modules (DOMs), buried in one cubic kilometer of Antarctic ice. When a neutrino interacts with a molecule in the ice, blue light is emitted from the resulting secondary charged particles through a process called Cherenkov radiation. The light then travels through the ice and can reach some of the DOMs, where it is detected. Researchers can then reconstruct the energy and direction of the particle, a process that relies on knowledge of the optical properties of ice.
In 2013, the IceCube collaboration reported a unique observation where the observed brightness of a light source depends on the direction of the light, an effect called “optical ice anisotropy”. So far, researchers have attempted to describe anisotropy with impurity-induced variations in absorption and scattering with limited success.
In a new study submitted to The Cryosphere, IceCube reports an optical effect that has not been previously described. The effect is the result of the birefringent properties of elongated ice crystals which bend light in two directions. The new insights gained have been incorporated into a new birefringence-based optical model of ice used in detector simulation, SpiceBFR, which has significantly improved the interpretation of light patterns resulting from particle interactions in ice.
“The optical model of ice used by the IceCube collaboration has been in development since the early days of the previous AMANDA experiment,” said Dmitry Chirkin, associate scientist at the University of Wisconsin-Madison. “For more than 20 years we have added elements of discovery to our understanding of ice, including the disappearance of trapped air bubbles at depths well above the detector and that at deeper depths the The South Pole ice cap contains the cleanest ice on the planet. Another discovery is the optical anisotropy of ice, which is the main subject of the study that was prompted by the new understanding of our paper.”
To improve on previous attempts to describe anisotropy, the collaborators looked closely at the anisotropy effect, finding a correlation between the deep development of ice crystal properties and the anisotropy effect. This led the researchers to believe that the many small, randomly-assorted crystals that make up the ice were at play in the observed anisotropy.
“Things really started when we realized that curved photon trajectories with tiny subdegree deviations per meter would be able to accurately describe the data,” said Johannes Gutenberg University researcher Dr Martin Rongen. of Mainz (JGU) and leader on the an analysis. “Indeed, when calculating and simulating the scattering of light through polycrystalline ice as present in IceCube, where the crystals are on average elongated along the direction of ice flow , a mean deviation occurs.”
For the study, the researchers ran simulations that modeled different paths that light could travel through the detector. They then compared the simulated data with a large set of calibration data extracted from IceCube. The IceCube calibration dataset includes data from 60,000 LEDs, equipped with all DOMs, that emit coherent light pulses into the ice, which are then used to calibrate the optical properties of the ice. From the comparison, the researchers were able to deduce the average shape and size of the ice crystals in IceCube. This exciting new discovery prompts the generation of new simulations and the adaptation of current reconstruction methods to account for the SpiceBFR model.
Not only will this new understanding help IceCube improve reconstructed neutrino interactions, but it also has implications for the field of glaciology as a whole. “The properties of ice crystals are studied in particular to understand the mechanics of ice flow, which can then be used to predict the mass balance of Antarctica and the resulting sea level rise. in a changing climate,” Rongen said.
Probing high-energy neutrinos associated with a blazar
Rasha Abbasi et al, In Situ Estimation of Ice Crystal Properties at the South Pole Using LED Calibration Data from the IceCube Neutrino Observatory (2022). DOI: 10.5194/tc-2022-174
Provided by Universitaet Mainz
Quote: Newly Discovered Optical Effect Allows IceCube Neutrino Observatory to Infer Properties of Ice Crystals (2022, October 24) Retrieved October 24, 2022 from https://phys.org/news/2022-10-newly-optical -effect-icecube-neutrino. html
This document is subject to copyright. Except for fair use for purposes of private study or research, no part may be reproduced without written permission. The content is provided for information only.
#Newly #Discovered #Optical #Effect #IceCube #Neutrino #Observatory #Infer #Properties #Ice #Crystals