[Paper Review] First performance studies of a prototype for the CASTOR forward calorimeter at the CMS experiment

X. Aslanoglou, A. Cyz+7 more|ArXiv.org|Jun 17, 2007

Radiation Detection and Scintillator Technologies1 references3 citations

TL;DR

This paper presents first performance studies of a prototype for the CASTOR forward calorimeter in the CMS experiment at the LHC, using electron beam tests at CERN/SPS to evaluate different configurations of quartz-tungsten sampling calorimeter components. The key finding is that quartz plates provide higher light output and comparable energy resolution (≈2% at 80 GeV) compared to quartz fibres, with glass reflectors yielding better performance than foil reflectors, supporting quartz plates and APDs as promising options for the final detector design.

ABSTRACT

We present results on the performance of the first prototype of the CASTOR quartz-tungsten sampling calorimeter, to be installed in the very forward region of the CMS experiment at the LHC. This study includes GEANT Monte Carlo simulations of the Cherenkov light transmission efficiency of different types of air-core light guides, as well as analysis of the calorimeter linearity and resolution as a function of energy and impact-point, obtained with 20-200 GeV electron beams from CERN/SPS tests in 2003. Several configurations of the calorimeter have been tested and compared, including different combinations of (i) structures for the active material of the calorimeter (quartz plates and fibres), (ii) various light-guide reflecting materials (glass and foil reflectors) and (iii) photodetector devices (photomultipliers and avalanche photodiodes).

Motivation & Objective

• To evaluate the performance of different configurations of the CASTOR forward calorimeter prototype for use in the CMS experiment at the LHC.
• To compare the light output, energy resolution, and linearity of quartz plates versus quartz fibres as active materials in the calorimeter.
• To assess the impact of different light-guide reflector types (glass vs. foil) and photodetector devices (PMTs vs. APDs) on calorimeter response.
• To determine optimal detector geometry and component choices for achieving high resolution and uniformity in the very forward region (5.2 < η < 6.6).
• To provide a foundation for the final design of the CASTOR calorimeter based on beam test results and GEANT4 simulations.

Proposed method

• Conducted beam tests at CERN SPS using 20–200 GeV electron beams on a prototype calorimeter with multiple configurations.
• Used GEANT4 Monte Carlo simulations to model Čerenkov light transmission efficiency through various air-core light-guide geometries and reflector types.
• Tested four octant readout units with different combinations of: (1) quartz plate or fibre active materials, (2) glass or foil reflectors on light guides, and (3) Hamamatsu PMTs or avalanche photodiodes (APDs) as photodetectors.
• Measured calorimeter linearity, energy resolution, and response uniformity as functions of beam energy and impact point across different sectors (S1, J1, J2).
• Analyzed response dependence on radial distance from the calorimeter center and evaluated cross-talk and leakage between adjacent sectors.
• Optimized light-guide design using three parameters: NA of fibre, light-guide length (lg), and mode number (lm), to maximize efficiency and uniformity.

Experimental results

Research questions

• RQ1 How does the choice of active material (quartz plates vs. fibres) affect light output and energy resolution in the CASTOR prototype?
• RQ2 What is the relative performance of glass versus foil reflectors in air-core light guides for Čerenkov light transmission?
• RQ3 How does the photodetector type (PMT vs. APD) influence energy resolution and linearity in the prototype?
• RQ4 To what extent does the impact point of the beam affect the calorimeter response and resolution?
• RQ5 What light-guide geometry and reflector configuration yield the highest light transmission efficiency and uniformity?

Key findings

• Quartz plates produced approximately 10–15% higher light output than quartz fibres of equal effective thickness, with similar energy resolution.
• The relative energy resolution was ≈2% for 80 GeV electrons when using quartz plates with glass reflectors and Hamamatsu PMTs, and ≈3.5–4.0% with foil reflectors.
• The constant term (p₀) of the energy resolution was <1% for both quartz plate and fibre configurations when using the same PMT and glass reflector, indicating low intrinsic resolution degradation at high energies.
• The stochastic term (p₁) was 36% for quartz plates and 46% for fibres, indicating better resolution uniformity with plates.
• APDs showed potential as photodetectors but require further testing for radiation hardness, cooling, and voltage stabilization.
• Leakage between sectors was negligible for impact points >8 mm from the border; only points <3 mm from the edge showed degraded response and resolution.