Test-beam measurements of instrumented sensor planes for a highly compact and granular electromagnetic calorimeter

TL;DR

This paper presents the development and beam-test results of highly compact, granular sensor planes for an electromagnetic calorimeter, designed for precise positron measurements in the LUXE experiment.

Contribution

It introduces a novel sandwich calorimeter design with thin sensor planes and integrated readout, suitable for high-precision measurements in challenging experimental conditions.

Findings

Sensor plane prototypes show homogeneous response

Edge effects are characterized and minimized

Readout systems perform effectively in beam tests

Abstract

The LUXE experiment is designed to explore the strong-field QED regime in interactions of high-energy electrons from the European XFEL in a powerful laser field. One of the crucial aims of this experiment is to measure the production of electron-positron pairs as a function of the laser field strength where non-perturbative effects are expected to kick in above the Schwinger limit. For the measurements of positron energy and multiplicity spectra, a tracker and an electromagnetic calorimeter are foreseen. The expected number of positrons varies over ten orders of magnitude and has to be measured over a widely spread low-energy background. To overcome these challenges, a compact and finely segmented calorimeter is proposed. The concept of a sandwich calorimeter made of tungsten absorber plates interspersed with thin sensor planes is developed. The sensor planes comprise a silicon pad sensor, flexible Kapton printed circuit planes for bias voltage supply and signal transport to the sensor edge, all embedded in a carbon fiber support. The thickness of a sensor plane is less than 1 mm. A dedicated readout is developed comprising front-end ASICs in 130 nm technology and FPGAs to orchestrate the ASICs and perform data pre-processing. As an alternative, GaAs are considered with integrated readout strips on the sensor. Prototypes of both sensor planes are studied in an electron beam of 5 GeV. Results will be presented on the homogeneity of the response and edge effects.