Posted in | Quantum Physics

CALET Successfully Measures High Energy Electrons in Space

The CALET Cosmic Ray experiment, headed by Professor Shoji Torii from Waseda University in Japan, together with partners from LSU and other researchers in the U.S. and abroad, have successfully performed the high-precision measurement of cosmic-ray electron spectrum up to 3 tera electron volts (TeV) by employing the CALorimetric Electron Telescope (CALET) on the Japanese Experimental Module, the Exposed Facility on the International Space Station (ISS).

This experiment is the first to make instant measurements of such extreme energy electrons in space.

ISS showing the Japanese Experiment Module – External Facility (JEM-EF). Photo Credit: JAXA

The CALET team published their first findings in Physical Review Letters (November 1 issue).

The CALET experiment received funding from the Japanese Space Agency (JAXA), the Italian Space Agency (ASI), and NASA. John Wefel, professor emeritus in LSU’s Department of Physics & Astronomy, serves as the spokesperson for the U.S. CALET team, which includes LSU (lead U.S. institution), NASA Goddard Space Flight Center, Washington University, and the University of Denver. Other LSU researchers working with the project are PhD student Nick Cannady, research associates Doug Granger and Amir Javaid, former LSU undergraduate Anthony Ficklin, and professors of physics and astronomy Greg Guzik and Mike Cherry.

High energy electrons are difficult to measure, but important because they potentially provide information about nearby astrophysical sources of high energy radiation and/or dark matter, the initial results provide a hint of anticipated structure in the high energy spectrum, which may indicate the presence of a nearby source of high energy particles like a pulsar or the annihilation of dark matter.

Mike Cherry, LSU researcher

CALET was set up in the ISS in August 2015 and has been collecting scientific data since October 2015 with a goal of five operational years. CALET is the first Japanese-led space-based mission devoted to cosmic ray observations.

The origin and speeding up of cosmic rays are still one of the cosmic mysteries, and cosmic-ray electrons are one of the most crucial targets of high-energy cosmic ray research. However, so as to observe high-energy electrons, it is necessary to have (1) high-precision energy measurement of all cosmic ray particles, (2) sensitivity to identify the very unusual electron flux, and (3) the capability to detect electrons hidden under the < 1,000 times higher flux of cosmic ray protons. Thus the measurement of electrons beyond 1 TeV has been a tough goal to accomplish. The calorimeter of CALET, with its unique and critical capabilities, enables researchers to perform accurate measurement of cosmic-ray electrons into the TeV region owing to the long-term exposure available on the ISS.

This measurement shows the ability of CALET to perform a precise direct measurement of electrons beyond 1 TeV which was hard for earlier experiments. With five years of observations, CALET will accomplish approximately six times higher statistics compared to this first result, and will allow for lessening of the systematic indecisions, including that from the detector response. The project’s goal is to push the energy limit to 20 TeV and to attain the precise energy spectrum, hopefully making it possible to validate definitively the presence of adjacent astrophysical cosmic ray sources and/or to expose the nature of dark matter.

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