Measuring Radiation Lengths using a Pixel Telescope

Motivation

It is useful to know the radiation lengths of materials in order to accurately determine the potential scattering angle or conversion probability of particles that pass through said material. The radiation lengths of pure elements are well known, but mixtures, compounds and alloys have a less well known radiation length. There are also new materials being created for use in high energy physics detectors (such as glues for the silicon layers) that have unknown radiation lengths. Additionally, there are materials which have well known radiation lengths but complex structures, making the radiation length at a given position on the material harder to determine.

To this end, a tool has been created using a pixel telescope that will allow the radiation length of a material to be measured. The radiation length can be measured to an accuracy of approximately 5%, with the dominating error being the uncertainty of the energy at the test beam. The tool can produce 'maps' of the radiation length across the material, allowing for a measured knowledge of the radiation length which can be compared to the theoretical predictions.

This will help in the development of monte carlo simulations and the realisation of tracks within the detectors. It will also help in decision making for future upgrades where radiation length can be an important factor in the choice of materials.

Introduction

The radiation length can be measured using the highland formula. The formula relates the radiation length of a material with the energy of the particles passing through it and the width of the scattering (which is assumed gaussian). We can use a pixel telescope to measure the positions of the particles passing through a device under test (DUT) and then from this we can extract a scattering angle. If we do this for many particles then we can calculate a radiation length based on the width of the scattering angle distribution.

-- PhillipHamnett - 2015-01-05