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Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - CRD - Cosmic Ray Direct
Calibration of the Aerogel Tiles for the HELIX RICH
P. Allison, J. Beatty, L. Beaufore, Y. Chen, S. Coutu, E. Ellingwood, M. Gebharb, N. Green, D. Hanna, B. Kunkler, S.I. Mognet, R. Mbarek, K. McBride, K. Michaels, D. Muller, J. Musser, S. Nutter, S. O'Brien, N. Park, T. Rosin,* E. Schreyer, G. Tarle, M. Tabata, A. Tomasch, G. Visser, S. Wakely, T. Werner, I. Wisher, M. Yu
*corresponding author
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Pre-published on: 2019 July 22
Published on:
Abstract
HELIX (High Energy Light Isotope eXperiment) is a balloon-borne experiment designed to measure the chemical and isotopic abundances of light cosmic ray nuclei, especially the $^{\textrm{10}}\textrm{Be}/^{\textrm{9}}\textrm{Be}$ ratio over the energy range from 0.2 GeV/n to beyond 3 GeV/n. This is a key measurement for constraining cosmic-ray propagation models. The detector is a mass spectrometer, which is built around a 1 Tesla superconducting magnet and a high-resolution tracking system to determine particle rigidity. Time-of-flight counters and a ring-imaging Cherenkov detector (RICH) are used to measure velocities.

The proximity-focused RICH consists of a radiator made of aerogel tiles (refractive index
approximately 1.15) and a detector plane of silicon photomultipliers. For discrimination of
the $^{\textrm{9}}\textrm{Be}$ and $^{\textrm{10}}\textrm{Be}$ isotopes at high energy, the refractive index of the aerogel must be known to a precision of 0.07%. Given the manufacturing tolerances in the production process, the index must be mapped over the lateral extent of aerogel tiles on a fine grid. In this contribution, we describe and show initial results from procedures developed for this task. These include laser-deflection and electron-beam measurements.
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