On December 1930, groups of extraordinary and unknown microscopic particles were first observed by an Austrian physicist named Wolfgang Pauli. Since their discovery, these unveiled particles have been fascinating to numerous physicists and have alluded to them the solutions to the universe’s most misunderstood phenomenon. Eventually, scientists and researchers started to believe these particles, called neutrinos, were “Messengers from the space”. Neutrinos approached to physicists interestingly for some of the same reasons that pottery shards are important to archaeologists. Physicists now view Neutrinos as “key particles” that contain answers to  incomprehensible astrophysical phenomenon and have installed numbers of neutrino observatories around the world. Given the nature of these mysterious particles that travel fast as light, researchers in neutrino observatories are struggling to figure out questions beyond the neutrinos. But why are scientists so obsessive about this particle? What specifically are neutrinos? How and where are the scientists working to solve their curiosities?  For many years, physicists around the world have tried to reveal the secrets of universe through the study of these fascinating, but yet mysterious, particles: and neutrinos, the messengers, will unveil mysteries of universe.

  • History of Neutrinos

Even before the modern science technologies were adopted, Scientists started discussing about this “ghost” particle. This subatomic and massless particles gave scientists a great confusion when they knew nothing about its identities. An Austrian physicist Wolfgang Pauli (April 25, 1900 ~ December 5, 1958) first came up with an idea of neutrinos’ identity on December, 1930 while he was trying to explain the energy spectrum of beta decays. Wolfgang theorized the existence of this undetected particle when he saw the difference between the energy and angular momentum of the initial and final particles carried away by some undetected particles. Although the neutrinos were first theorized to exist in 1930, it took 26 years to prove its existence. In 1956, Clyde Cowan, F. B. Harrison, A. D. McGuire, Frederick Reines, and H. W. Kruse published their report on the experiment to prove neutrinos’ existence. Their report, known as “Detection of the Free Neutrino: a Confirmation” won them a Nobel prize in physics in 1995 and included series of experiment results. One experiment, titled “Cowan – Reines Neutrino Experiment”, was conducted at the Savannah River Plant near Augusta, Georgia for its suitable condition to shield a nuclear reactor against cosmic rays. Using nuclear reactor and a tank full of water, Cowan and Reines produced neutrino fluxes through beta decay in the reactor. Then they made neutrinos to react with protons in the water tank to produce neutrons and positrons. Following to this experiment, Cowan and Reines conducted another experiment to make their theory even more conclusive. Instead of water, they filled a tank with Cadmium Chloride (CdCl2) to absorb neutrinos since the Cadmium performs best to absorb neutrinos and eject gamma rays out when it comes into contact with neutrinos; It was used to conclude Cowan and Reines’ theory about the existence of neutrinos. It was not until 1962 when group of physicists, including Melvin Schwartz, Leon M. Lederman, and Jack Steinberger confirmed that more than one type of neutrinos exists. Existence of the “Muon Neutrino” was confirmed during their experiment at the Brookhaven National Lab near Upton, NY. The third and last type of neutrino, the Tau lepton was detected in 1978 at the Stanford Linear Accelerator. In 1985, The IMB Detector  was installed at Fairport Harbor, Ohio. Built 2000 feet underground, this gigantic neutrino observatory was primarily built to observe proton decay. 1987 was the year that this colossal observatory first detected simultaneous burst of 8 neutrinos that was emitted from Supernova 1987a. The year of 1996 was a year when the AMANDA Neutrino Telescope completed its installation near Amundsen-Scott station at Geographic South Pole. Unlike the other observatory, this telescope was specifically built for only neutrino detection. Containing optical modules that each contains a single photomultiplier tube, the telescope was built 1900 meters under an Antarctic icecap. In 1998, the Japanese neutrino observatory, Super-KamioKande detected the Neutrino Oscillation, which is known as one of the greatest discoveries from the history of neutrino studies. The first actual detection of tau neutrino was announced in the year of 2000 by the DONUT collaboration. After a decade, The NSF and University of Wisconsin-Madison completed construction of IceCube South Pole Neutrino Observatory, next to the AMANDA.

  • Neutrino Observatories and Discoveries   

Studying neutrino is one of the most challenging scrutiny that physicists are conducting in the history of science. Since neutrino is the one of the fastest and the lightest particles that barely interacts with other electrically charged particle, it takes extreme effort to detect a minute amount of neutrino, despite the installation of numerous detectors around the globe. In addition to the IceCube way down south, observatories, detectors and telescopes are installed all around the globe covering from USA to China, Japan, India, Argentina and Greece. Out of all those detectors around the world, the IceCube Neutrino Observatory and the Super-Kamiokande Observatory from Japan are the most recognized ones. The Super-Kamiokande Detector is a stainless-steel tank, 39.3m diameter and 41.4m tall, filled with 50,000 tons of ultra pure water. About 13,000 photo-multipliers are installed on the tank wall. The detector is located at 1,000 meter underground Hida-city, Gifu, Japan. The Super-KamioKande Observatory is recognized for the discovery of neutrino oscillation and the detection of neutrino from supernova burst in 1987 after the explosion of supernova 1987a. The neutrino oscillation was discovered by Super-KamioKande observatory in 1998 which verified that the neutrino actually had finite mass although it is extremely infinitesimal. This observatory began its observation on the first day of April 1996 after 5 years of construction. While The Super-Kamiokande detector is known for its discovery of neutrino oscillation, the IceCube Neutrino Observatory is known for its size, and uniqueness. What special about the IceCube is that it is built on a Geographic South Pole. It is built adjacent to the Amundsen-Scott South Pole station, and the AMANDA telescope for South Pole’s perfect condition to preserve neutrinos under the pure, clear and stable Antarctic ice sheet. The detector is buried 2500 meters under the Antarctic ice sheets, covering a cubic kilometer of ice. The detector is comprised of 86 cables each consisting total of 60 DOMs (Digital Optical Modules). The total of 5160 DOMs buried underground contain extremely sensitive Photomultiplier tubes which are used to detect interaction with any lights, and microcomputers that deliver gathered information to the laboratory at the Amundsen-Scott Station. Every day, 100 gigabytes of the gathered information from the DOMs are conveyed to the satellites for a precise analysis. The construction of the IceCube began in 2004 when the funding and construction was approved, and was completed on December 18, 2010. The total cost of the construction was $279 million and NSF funded about $242 million according to University of Wisconsin-Madison. The achievements and progress IceCube is showing so far is proving that South Pole is absolutely perfect place to study this subatomic particle. Scientists at IceCube observed the first astrophysical high-energy neutrino flux and the highest energy cosmic neutrino ever seen, discovering three neutrino events at the highest energy level. Today, about 300 physicists and engineers from 47 different institutes stay at IceCube, elaborating about the neutrino oscillation and relationship between neutrinos and astrophysics.

  • Why do Scientists study neutrinos?

Ever since the identity of neutrino was first proved in 1956, scientists started establishing observatories around the world to learn more about the neutrinos. Numerous experiments were conducted by physicists, most of them failed to detect neutrinos simply because they lacked information about this veiled particle. But why are the scientists never stop attempting? Despite the countless failures, patience and elaboration by physicists resulted in the brand new discoveries that would revolutionize the study of astrophysics. Starting from the discoveries of muon and tau neutrinos, the detection of the neutrinos from the Supernova 1987a, neutrino oscillations from Super-KamioKande observatory, and finally, the highest energy cosmic neutrino from IceCube affected scientists and fascinated many people. The major reason neutrino is so significant particle has something to do with its origin and properties. Neutrinos are pretty much produced from everywhere. It can be produced from the nuclear reactor, sun or even from the radioactive decay of Carbon in human’s body. But out of all the neutrinos, the highest energy neutrinos come from far out in the space, where all the black holes and supernovas are. Neutrinos travel nearly as fast as light from one end of the universe without being deflected by any magnetic fields, which imply scientists that it travels through Earth instantly without losing data of its birth place. Because neutrinos traverse through Earth so quickly without loss of data, this makes neutrinos excellent messengers of information about its origin. Neutrino belongs to the most misunderstood astrophysical events in the universe such as supernova, galactic nuclei, and the black holes. Furthermore, physicists could get a basic idea about what the dark matter and dark energy could be by collecting precise data of the exact origins of neutrinos because the neutrinos are predicted to have strong correlation with dark matters. Dark matter is non luminous and hypothetical matter that is thought to be account for gravitational forces in the universe. Dark energy is also hypothetical form of energy whose negative pressure counteracts gravity and is postulated to be responsible for the universe expanding at an accelerating rate. Dark matter and Dark energy are hypothetical ideas of the unknown matter and energy that are strongly believed to be related to expansion of the universe. According to icecube.wisc.edu, Dark matter and Dark energy make up about 96% of our universe composition. Although no one knows when or how physicists will be able to reveal secrets of the universe, they will continue to study about neutrinos, because neutrino is the “key” particle that contains the clue for the discoveries of our universe’s secrets.