First Measurements Of The Spectral And Angular Distribution Of Transition Radiation Using A Silicon Pixel Sensor On A Timepix3 Chip

X-ray Transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. Particle identification is often achieved based on a threshold effect of the X-ray transition radiation (TR). In most of the detectors, TR emission starts at gamma factors above similar to 500 and reaches saturation at gamma similar to 2 - 3.10(3). However, many experiments require particle identification up to gamma similar to 10(5), which is difficult to achieve with current detectors, based only on the measurement of the photon energy together with the particle ionization losses. Additional information on the Lorentz factor can be extracted from the angular distribution of TR photons. TRDs based on pixel detectors give a unique opportunity for precise measurements of spectral and angular distributions of TR at the same time. A 500 um thick silicon sensor bump bonded to a Timepix3 chip was used in a test beam measurement at the CERN SPS. A beam telescope was employed to separate clusters produced by the primary beam particles from the potential TR clusters. Spectral and angular distributions of TR were studied with high precision for the first time using beams of pions, electrons and muons at different momenta. In this paper, the measurement and analysis techniques are described, and first results are presented.