Mapping the material distribution of a complex structure in an electron beam

TL;DR

This paper introduces a high-resolution method to map the material distribution in complex detector structures using electron scattering data, improving accuracy over traditional averaging techniques.

Contribution

It presents a novel approach for detailed material mapping in large-scale detectors by analyzing electron scattering angles and hit positions.

Findings

High spatial resolution material maps achieved

Method effective for inhomogeneous structures

Requirements for data quality and correction techniques identified

Abstract

The simulation and analysis of High Energy Physics experiments require a realistic simulation of the detector material and its distribution. The challenge is to describe all active and passive parts of large scale detectors like ATLAS in terms of their size, position and material composition. The common method for estimating the radiation length by weighing individual components, adding up their contributions and averaging the resulting material distribution over extended structures provides a good general estimate, but can deviate significantly from the material actually present. A method has been developed to assess its material distribution with high spatial resolution using the reconstructed scattering angles and hit positions of high energy electron tracks traversing an object under investigation. The study presented here shows measurements for an extended structure with a highly inhomogeneous material distribution. The structure under investigation is an End-of-Substructure-card prototype designed for the ATLAS Inner Tracker strip tracker -- a PCB populated with components of a large range of material budgets and sizes. The measurements presented here summarise requirements for data samples and reconstructed electron tracks for reliable image reconstruction of large scale, inhomogeneous samples, choices of pixel sizes compared to the size of features under investigation as well as a bremsstrahlung correction for high material densities and thicknesses.