Radiation length imaging with high resolution telescopes

TL;DR

This paper demonstrates high-resolution radiation length imaging of vertex detector prototypes using test beam experiments, enabling detailed 2D material profiling at micrometer scales.

Contribution

It introduces a method for precise 2D radiation length imaging with high spatial resolution using particle scattering measurements in test beam setups.

Findings

Achieved 30 μm spatial resolution in radiation length imaging.

Successfully distinguished complex material profiles of detector prototypes.

Collected 100 million tracks at 4 GeV for detailed analysis.

Abstract

The construction of low mass vertex detectors with a high level of system integration is of great interest for next generation collider experiments. Radiation length images with a sufficient spatial resolution can be used to measure and disentangle complex radiation length $X$/$X_0$ profiles and contribute to the understanding of vertex detector systems. Test beam experiments with multi GeV particle beams and high-resolution tracking telescopes provide an opportunity to obtain precise 2D images of the radiation length of thin planar objects. At the heart of the $X$/$X_0$ imaging is a spatially resolved measurement of the scattering angles of particles traversing the object under study. The main challenges are the alignment of the reference telescope and the calibration of its angular resolution. In order to demonstrate the capabilities of $X$/$X_0$ imaging, a test beam experiment has been conducted. The devices under test were two mechanical prototype modules of the Belle II vertex detector. A data sample of 100 million tracks at $4\, \mathrm{GeV}$ has been collected, which is sufficient to resolve complex material profiles on the $30\,\mu$m scale.