[Paper Review] Hadron calorimeter with MAPD readout in the NA61/SHINE experiment

A. Ivashkin, F. Akhmadov+21 more|arXiv (Cornell University)|May 22, 2012

Radiation Detection and Scintillator Technologies3 citations

TL;DR

This paper presents a modular lead-scintillator hadron calorimeter with micro-pixel avalanche photodiodes (MAPDs) for the NA61/SHINE experiment at CERN, designed to measure projectile spectators in heavy-ion collisions. The calorimeter uses 44 segmented modules with WLS-fiber light readout and MAPD-3A photodetectors (15,000 pixels/mm²) to achieve linear response up to 6×10⁴ photons, demonstrating 6.5% energy resolution at 30 GeV and stable operation in beam tests.

ABSTRACT

The modular hadron calorimeter with micro-pixel avalanche photodiodes readout for the NA61/SHINE experiment at the CERN SPS is presented. The calorimeter consists of 44 independent modules with lead-scintillator sandwich structure. The light from the scintillator tiles is captured by and transported with WLS-fibers embedded in scintillator grooves. The construction provides a longitudinal segmentation of the module in 10 sections with independent MAPD readout. MAPDs with pixel density of $~10^{4}$/mm$^2$ ensure good linearity of calorimeter response in a wide dynamical range. The performance of the calorimeter prototype in a beam test is reported.

Motivation & Objective

• To develop a high-resolution hadron calorimeter for the NA61/SHINE experiment to study the phase diagram of strongly interacting matter.
• To measure the number of non-interacting nucleons (projectile spectators) in ion-ion collisions to probe the critical point and onset of deconfinement.
• To ensure excellent energy resolution (σE/E < 60%/√E) and transverse uniformity in the presence of large fluctuations from collision geometry.
• To validate the use of high-density MAPDs (15,000 pixels/mm²) for linear response in high-intensity hadronic showers.
• To demonstrate stable, linear performance of the calorimeter prototype under beam conditions across a wide energy range (1–158 GeV).

Proposed method

• The calorimeter consists of 44 independent modules, each with 60 lead (16 mm) and scintillator (4 mm) layers, forming 5.7 nuclear interaction lengths.
• Light from scintillator tiles is collected via WLS-fibers embedded in grooves and routed to 10 longitudinal sections per module, each read out by a single MAPD.
• MAPD-3A photodetectors with 15,000 pixels/mm² and 3×3 mm² active area are used for high dynamic range and linearity.
• The system uses a muon beam scan to calibrate 90 readout channels across nine 3×3 cm² modules for energy response uniformity.
• Energy resolution is measured using hadron beams (20–158 GeV at SPS, 1–6 GeV at PS), with corrections applied for lateral shower leakage (16% estimated).
• A three-term resolution model (stochastic, constant, and leakage terms) is fitted to data to extract resolution parameters.

Experimental results

Research questions

• RQ1 Can high-density MAPDs (15,000 pixels/mm²) provide linear response to light pulses with up to 6×10⁴ incident photons in a hadron calorimeter?
• RQ2 Does the modular lead-scintillator design with WLS-fiber readout and MAPD readout achieve the required energy resolution of <60%/√E at 30 GeV?
• RQ3 To what extent does lateral shower leakage affect energy resolution in a 30×30 cm² prototype, and can it be corrected?
• RQ4 Is the MAPD-3A photodetector stable and linear under continuous beam operation at intensities expected in NA61/SHINE?
• RQ5 Can the calorimeter prototype accurately distinguish electromagnetic-like responses (e.g., positron deposits) from hadronic showers?

Key findings

• The MAPD-3A photodetectors exhibit linear response to light pulses with up to 6×10⁴ incident photons, corresponding to a maximum of 15,000 photoelectrons, with less than 5% amplitude drop at the highest expected beam intensity.
• The energy resolution for positron deposits at 30 GeV was measured at 6.5%, consistent with the target requirement of <60%/√E.
• The fitted three-term resolution model yields a stochastic term of 56.1% and a constant term of 2.1%, with a fixed leakage term of 16%, indicating partial compensation but non-ideal sampling.
• The prototype demonstrated stable operation over two months of calibration and beam runs, with 320 MAPD-3A samples installed and functioning reliably.
• The calorimeter's longitudinal segmentation into 10 sections enables particle-type discrimination and improves light collection uniformity.
• Monte Carlo simulations confirmed that lateral shower leakage of ~16% in the 30×30 cm² prototype is a significant contributor to resolution degradation, justifying larger-scale testing.