Advanced Thin Ionization Calorimeter

Advanced Thin Ionization Calorimeter

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The Advanced Thin Ionization Calorimeter (ATIC) is a balloon
Balloon (aircraft)
A balloon is a type of aircraft that remains aloft due to its buoyancy. A balloon travels by moving with the wind. It is distinct from an airship, which is a buoyant aircraft that can be propelled through the air in a controlled manner....

-borne instrument flying in the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 over Antarctica to measure the energy and composition of cosmic rays. ATIC was launched from McMurdo Station
McMurdo Station
McMurdo Station is a U.S. Antarctic research center located on the southern tip of Ross Island, which is in the New Zealand-claimed Ross Dependency on the shore of McMurdo Sound in Antarctica. It is operated by the United States through the United States Antarctic Program, a branch of the National...

 for the first time in December 2000 and has since completed three successful flights out of four.

Working principle


The detector uses the principle of ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 calorimetry
Calorimetry
Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat...

: several layers of the scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...

 bismuth germanate
Bismuth germanate
Bismuth germanium oxide is an inorganic chemical compound with main use as a scintillator. It forms cubic crystals....

 emit light as they are struck by particles, allowing to calculate the particles' energy. A silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 matrix is used to determine the particles' electrical charge.

Collaborators


The project is an international collaboration of researchers from Louisiana State University
Louisiana State University
Louisiana State University and Agricultural and Mechanical College, most often referred to as Louisiana State University, or LSU, is a public coeducational university located in Baton Rouge, Louisiana. The University was founded in 1853 in what is now known as Pineville, Louisiana, under the name...

, University of Maryland, College Park
University of Maryland, College Park
The University of Maryland, College Park is a top-ranked public research university located in the city of College Park in Prince George's County, Maryland, just outside Washington, D.C...

, Marshall Space Flight Center
Marshall Space Flight Center
The George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...

, Purple Mountain Observatory
Purple Mountain Observatory
Purple Mountain Observatory , also known as Zijinshan Astronomical Observatory, is an astronomical observatory located on the Purple Mountain in Nanjing, China.The long time director of the observatory was Zhang Yuzhe Purple Mountain Observatory , also known as Zijinshan Astronomical Observatory,...

 in China, Moscow State University
Moscow State University
Lomonosov Moscow State University , previously known as Lomonosov University or MSU , is the largest university in Russia. Founded in 1755, it also claims to be one of the oldest university in Russia and to have the tallest educational building in the world. Its current rector is Viktor Sadovnichiy...

 in Russia and Max Planck Institute for Solar System Research
Max Planck Institute for Solar System Research
The Max Planck Institute for Solar System Research is a research institute in Astronomy/Astrophysics, located in Lindau , Germany; 20 km north east of Göttingen. The exploration of our solar system is the central theme for the scientific research done at this Institute...

 in Germany. ATIC is supported in the United States by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 and flights are conducted under the auspices of the Balloon Program Office at Wallops Flight Facility
Wallops Flight Facility
Wallops Flight Facility , located on the Eastern Shore of Virginia, is operated by NASA’s Goddard Space Flight Center, primarily as a rocket launch site to support science and exploration missions for NASA and other U.S. government agencies...

 by the staff of the Columbia Scientific Balloon Facility
Columbia Scientific Balloon Facility
The Columbia Scientific Balloon Facility is a NASA facility responsible for providing launch, tracking and control, airspace coordination, telemetry and command systems, and recovery services for unmanned, high altitude balloons...

. Antarctic logistics are provided by the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 and its contractor Raytheon
Raytheon
Raytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...

 Polar Services Corporation.
The principal investigator for ATIC is John Wefel of Louisiana State University.

Results


In November 2008, researchers published in Nature
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...

the finding of a surplus of high energy electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s. During a 5-week observatory period in 2000 and 2003, ATIC counted 70 electrons with energies in the range 300-800 GeV; these electrons were in excess of those expected from the galactic background. The source of these electrons is unknown, but it is assumed to be relatively close, no more than about 3000 lightyears away, since high energy electrons rapidly lose energy as they travel through the galactic magnetic field and collide with photons. The electrons could originate from a nearby pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...

 or other astrophysical object, but the researchers were not able to identify a fitting object. According to another conjecture, the electrons result from collisions of Dark Matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

 particles, for example WIMP Kaluza-Klein particle
Kaluza–Klein theory
In physics, Kaluza–Klein theory is a model that seeks to unify the two fundamental forces of gravitation and electromagnetism. The theory was first published in 1921. It was proposed by the mathematician Theodor Kaluza who extended general relativity to a five-dimensional spacetime...

s of mass near 620 GeV.

Related data from other experiments


Earlier in the year, the satellite PAMELA had found excess positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...

s (the antiparticle
Antiparticle
Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...

 of the electron) in the cosmic ray signal, also believed to originate from dark matter interactions.
ATIC cannot distinguish between electrons and positrons, so it is possible that the two results are compatible.

On the other hand, in November 2008 the Milagro experiment
Milagro (experiment)
Milagro, , was a ground based water Čerenkov radiation telescope situated in the Jemez Mountains near Los Alamos, New Mexico at the Fenton Hill Observatory site. It was primarily designed to detect gamma rays but also detected large numbers of cosmic rays. It operated in the TeV region of the...

 reported cosmic ray "hotspots" in the sky, possibly supporting astrophysical objects as sources of the surplus electrons. In May 2009, observations by the Fermi space telescope were reported which did not support the spike of high-energy electrons seen by ATIC.

External links