Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - CRI - Cosmic Ray Indirect
TALE FD Cosmic Rays Composition Measurement
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Pre-published on: 2019 July 22
Published on:
Abstract
The Telescope Array (TA) cosmic rays detector located in the
State of Utah in the United States is the largest ultra high energy
cosmic rays detector in the northern hemisphere. The Telescope Array
Low Energy Extension (TALE) fluorescence detector (FD) was added to
TA in order to lower the detector's energy threshold, and has succeeded
in measuring the cosmic rays energy spectrum down to PeV energies. In
this contribution we describe a measurement of the cosmic rays
composition using TALE FD data collected over a period of $\sim4$ years.
TALE FD data is used to measure the $X_{max}$ distributions of showers seen
in the energy range of $10^{15.3}$ - $10^{18.3}$~eV. An increase in the
$X_{max}$ elongation rate is observed at energies just above $10^{17}$~eV
indicating a change in the cosmic rays composition from a heavier to a
lighter mix of primaries.
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