[Paper Review] Study of Micro Pixel Photon Counters for a high granularity scintillator-based hadron calorimeter

N. d’Ascenzo, A. Eggemann+1 more|ArXiv.org|Nov 8, 2007

Radiation Detection and Scintillator Technologies3 references3 citations

TL;DR

This study evaluates Micro Pixel Photon Counters (MPPCs) for direct readout in a high-granularity scintillator-based hadron calorimeter for the International Linear Collider (ILC). The MPPC enables efficient detection of blue scintillation light with 97% signal collection efficiency at 6–7 photoelectrons per minimum ionizing particle (mip), outperforming traditional wavelength-shifting fiber coupling in dynamic range and efficiency, making it a viable, simplified alternative to current SiPM-based designs.

ABSTRACT

A new Geiger mode avalanche photodiode, the Micro Pixel Photon Counter (MPPC), was recently released by Hamamatsu. It has a high photo-detection efficiency in the 420 nm spectral region. This product can represent an elegant candidate for the design of a high granularity scintillator based hadron calorimeter for the International Linear Collider. In fact, the direct readout of the blue scintillation photons with a MPPC is a feasible techological solution. The readout of a plastic scintillator by a MPPC, both mediated by the traditional wavelength shifting fiber, and directly coupled, has been systematically studied.

Motivation & Objective

• To assess the feasibility of using new-generation MPPCs for direct readout of blue-emitting scintillators in high-granularity hadron calorimeters.
• To compare the performance of direct MPPC coupling with conventional green wavelength-shifting fiber-mediated readout in plastic scintillators.
• To determine the signal collection efficiency, dark noise, and dynamic range of MPPCs at various overvoltages for ILC-level requirements.
• To evaluate the potential of MPPCs to replace current SiPMs in the CALICE HCAL prototype with improved performance and simplified geometry.
• To investigate the impact of pixel count (400 vs. 1600) on signal linearity, uniformity, and dynamic range.

Proposed method

• A 3×3×0.5 cm³ plastic scintillator tile was directly coupled to a 1600- or 400-pixel MPPC, with no optical coupling agent, ensuring reproducible contact within 3%.
• A second configuration used a green wavelength-shifting fiber (Y11(200)) embedded in the scintillator to couple light to the MPPC, mimicking the current CALICE prototype.
• The MPPC response to minimum ionizing particles (mip) was measured using a ¹⁰⁶Ru β-source, with signals amplified and integrated via a QDC in 80 ns coincidence gate.
• The most probable value (MPV) of photoelectron yield was extracted by fitting the MPPC pulse amplitude spectrum with a multi-Gaussian function and analyzing peak areas.
• Signal collection efficiency was calculated by defining a threshold based on pedestal noise and measuring the fraction of mip signal above that threshold.
• Dark rate, cross-talk, and gain were characterized at different overvoltages (2.5–3.5 V above breakdown) to assess noise performance under ILC occupancy constraints.

Experimental results

Research questions

• RQ1 Can MPPCs directly detect blue scintillation light from plastic scintillators with sufficient efficiency and signal-to-noise ratio for ILC hadron calorimetry?
• RQ2 How does the signal collection efficiency of MPPCs compare between direct coupling and wavelength-shifting fiber-mediated readout?
• RQ3 What is the optimal overvoltage for MPPCs to balance high signal collection efficiency and low dark noise for ILC trigger requirements?
• RQ4 How does pixel count (400 vs. 1600) affect dynamic range and linearity in MPPC-based calorimeter readout?
• RQ5 Can MPPCs achieve performance comparable or superior to current SiPMs in the CALICE HCAL prototype, particularly in dynamic range and signal uniformity?

Key findings

• The 1600-pixel MPPC achieved a signal collection efficiency of 97% at 2.5–3.5 V over breakdown, with a most probable number of 6–7 photoelectrons per minimum ionizing particle (mip).
• The 400-pixel MPPC showed 98% signal collection efficiency but limited dynamic range due to fewer pixels, constraining its use in high-intensity environments.
• The MPPC dark rate was measured at 40 kHz (1600-pixel) and 230 kHz (400-pixel) at 0.5-pixel threshold, with cross-talk of 4.3% and 3.5% respectively, both below ILC occupancy thresholds when operated above 2–4 pixels threshold.
• Direct coupling of the MPPC to the scintillator yielded a 97% signal collection efficiency, comparable to the fiber-mediated method, but with a broader dynamic range due to higher pixel count.
• The MPPC performance in both direct and fiber-mediated readout surpassed current SiPMs in signal efficiency (98%) and dynamic range, especially at higher overvoltages.
• The study confirms that MPPCs are a viable, simplified alternative to SiPMs in high-granularity calorimeters, with potential for improved performance and reduced system complexity.