Measurements of Compton Scattered Transition Radiation at High Lorentz Factors

TL;DR

This paper reports on the development and testing of a novel Compton Scatter Transition Radiation Detector (TRD) capable of measuring extremely high Lorentz factors in relativistic particles, surpassing previous energy detection limits.

Contribution

The study introduces a high Lorentz factor optimized Compton Scatter TRD with conducting aluminum foils, demonstrating enhanced performance and higher energy measurement capabilities.

Findings

Effective separation of transition radiation from background using Compton scattering.

Conducting aluminum foils outperform nonconducting plastic foils.

Ability to measure particle energies an order of magnitude higher than previous methods.

Abstract

X-ray transition radiation can be used to measure the Lorentz factor of relativistic particles. Standard transition radiation detectors (TRDs) typically incorporate thin plastic foil radiators and gas-filled x-ray detectors, and are sensitive up to \gamma ~ 10^4. To reach higher Lorentz factors (up to \gamma ~ 10^5), thicker, denser radiators can be used, which consequently produce x-rays of harder energies (>100 keV). At these energies, scintillator detectors are more efficient in detecting the hard x-rays, and Compton scattering of the x-rays out of the path of the particle becomes an important effect. The Compton scattering can be utilized to separate the transition radiation from the ionization background spatially. The use of conducting metal foils is predicted to yield enhanced signals compared to standard nonconducting plastic foils of the same dimensions. We have designed and built a Compton Scatter TRD optimized for high Lorentz factors and exposed it to high energy electrons at the CERN SPS. We present the results of the accelerator tests and comparisons to simulations, demonstrating 1) the effectiveness of the Compton Scatter TRD approach; 2) the performance of conducting aluminum foils; and 3) the ability of a TRD to measure energies approximately an order of magnitude higher than previously used in very high energy cosmic ray studies.