Every other week, Ruchi Shah, a biology major, will take a look at Stony Brook-related research and science news.
Scientists from Stony Brook University that are part of the international team at the IceCube South Pole Neutrino Observatory were first to detect particles called neutrinos that originated from astrophysical sources.
This feat, which was recently published in Science, involved more than seven years of construction and data collection in one of the coldest places on Earth, the South Pole.
As Dr. Joanna Kiryluk, assistant professor of physics at Stony Brook University, explained, the IceCube detector that was built to detect neutrinos is one cubic kilometer in size and is buried 1.5 kilometers deep in the Antarctic ice. IceCube is the largest neutrino detector ever built and the rationale behind its location was two-fold.
First, ice was selected as the medium because of its excellent optical properties. Second, there is plenty of free material—ice—available for use in Antarctica. The detector is comprised of 86 uniformly placed holes and in each hole there is a string attached to 60 “balls” (Digital Optical Modules, DOMs). These DOMs are equipped with photomultipliers, which detect light emitted by particles created in the process of neutrinos interacting in the ice.
Essentially, the DOMs record the intensity of light as a function of time and send corresponding data back to the base for analysis. Scientists like Kiryluk then piece together the charge recorded by each optical module to produce an overall picture of the pattern. They can then deduce if the pattern is a result of background material or a result of a specific type (“flavor”) of neutrino.
The way that the neutrinos’ events are characterized and analyzed is similar to using a blender to make juice. When a tomato hits the blade of a blender, a red juice is created. Likewise, a blueberry creates a characteristic blue juice, and pineapple creates yellow juice.
In the same way, Kiryluk is interested in three different types or flavors of neutrinos, each of which create their own characteristic pattern when they hit particles inside the nuclei of atoms that comprise ice.
For example, electron neutrinos produce light in a spherical pattern when they hit, muon neutrinos produce light that propagates in a line, and tau neutrinos produce light that—depending on their energy—can be one of those two patterns.
This IceCube detector can be seen simply as a type of telescope. As opposed to telescopes, which normally capture direct light from distant astronomical objects, this detector is built to capture neutrinos. Neutrinos are tiny, almost massless subatomic particles that travel at almost the speed of light. What makes them special is that they travel in a straight line from their source without being deflected by magnetic fields or being absorbed by matter. Therefore, they carry a vast amount of information with them regarding their origin.
Neutrinos are also fascinating because they are emitted from some of the least understood events in the universe like black holes, supernovas and active galactic nuclei. IceCube was built to analyze neutrinos coming from such astrophysical sources.
Kiryluk and her team analyze the IceCube data to select astrophysical neutrinos to better understand the mechanism and rules that govern the astrophysical objects that emitted the neutrinos.
The IceCube usually encounters and detects hundreds of thousands of neutrino events in a year. Almost all of them are created in the Earth atmosphere and are considered to be background for cosmic neutrinos.
So far IceCube detected two large (high energy) electron-type neutrino events along with others. The two large events, spanning the size of more than one-fourth of the entire Stony Brook campus, had about 1,000 times the amount of energy produced by the Large Hadron Collider, where the Higgs particle was discovered.
These events, named after the Sesame Street characters Bert and Ernie, are the highest energy neutrino events ever observed. The events, reported in Nov. 22, 2013 issue of Science magazine, are the first evidence for astrophysical neutrinos, even though their origin is not yet known.
The analysis of future data collected with the IceCube detector will provide Kiryluk and her team with a better understanding of astrophysical objects in the Universe.