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Description
Highly compact and highly granular electromagnetic calorimeters are required for precision luminosity measurements at future e⁺e⁻ colliders. Such detectors are also essential for determining the positron multiplicity and energy spectra in the LUXE experiment [1], which investigates strong-field QED through laser–electron interactions.
In a luminometer, where Bhabha scattering serves as the gauge process, a compact sampling calorimeter with a small Molière radius enables a precise definition of the fiducial volume, improves the separation of electromagnetic showers from low-energy background, and reduces the required detector space. The proposed calorimeter design consists of alternating tungsten absorber plates and thin silicon detector layers. A similar design is needed to cover a large range of positron multiplicities the LUXE experiment. A partially instrumented multi-plane prototype with up to 11 silicon detector layers was tested in 1–6 GeV electron beams at the DESY II synchrotron. Each detector plane consists of a silicon pad sensor mounted on flexible Kapton circuits and supported by a lightweight carbon-fiber structure, enabling highly compact instrumentation with sub-millimeter thickness.
The detector planes were installed in 1.2 mm gaps between tungsten absorber plates corresponding to one radiation length each. Each plane consists of a 90 × 90 mm² silicon pad sensor segmented into a 16 × 16 matrix. The readout electronics, positioned outside of the stack, employs FLAME [2] ASICs integrating analogue front-end electronics and 10-bit ADCs.High-statistics data were collected to perform precise detector alignment and to investigate the longitudinal and transverse development of electromagnetic showers. Preliminary results on energy, position, and angular resolution, as well as measurements of the Molière radius and shower development, are presented. The current status of the prototype development and comparisons with simulation studies are also discussed .
[1]. Abramowicz, H., Almanza Soto, M. et al., Technical Design Report for the LUXE experiment., Eur. Phys. J. Spec. Top. 233, 1709–1974 (2024). https://doi.org/10.1140/epjs/s11734-024-01164-9
[2]. Mirosław Firlej et al 2026 JINST 21 P03005
The measurements leading to these results have been performed at the Test Beam Facility at DESY Hamburg (Germany), a member of the Helmholtz Association (HGF).