Contribution of the light-collection non-uniformity to the energy resolution for the spaghetti-type calorimeter modules

TL;DR

This paper investigates how non-uniform light collection in spaghetti-type calorimeters affects their energy resolution, using optical simulations to evaluate different light guide geometries for potential use in HL-LHC experiments.

Contribution

It provides a detailed simulation-based analysis of light collection non-uniformity impacts on energy resolution in SpaCal modules, exploring various light guide designs.

Findings

Non-uniformities significantly affect energy resolution.

Certain light guide geometries improve light collection uniformity.

Simulation results guide optimal light guide design choices.

Abstract

Spaghetti-type calorimeters (SpaCal) are being considered as a potential solution for experiments at the High-Luminosity Large Hadron Collider (HL-LHC). SpaCal modules consist of an absorber block with a matrix of holes filled with scintillating fibres. This geometry offers a flexible granularity. However, the total number of scintillating fibres per channel could exceed the available photocathode surface area, necessitating a light guide to efficiently collect and register the scintillating light from the scintillating fibres to a photomultiplier. The non-uniformities in the light collection would impact the energy resolution of the detector. In this study, the impact of the light collection non-uniformity on the energy resolution is estimated for the various geometries of light guides using optical simulations~(GEANT4 simulation with optical photons). The study performed assumed a SpaCal prototype with $30\times 30$~mm$^2$ cell size and photomultipliers featuring realistic entrance window shapes and sizes, and explores different light guide designs.