Study of Particle Fluence Effects on Collected Charge and Depletion Voltage of the ATLAS IBL Planar Pixel Sensors

TL;DR

This study investigates how particle fluence impacts charge collection and depletion voltage in ATLAS IBL pixel sensors over ten years of LHC operation, using experimental data and simulations.

Contribution

It provides a detailed analysis of sensor degradation due to radiation damage, combining empirical measurements with TCAD and Monte Carlo modeling.

Findings

Collected charge decreases with increasing fluence.

Depletion voltage increases as sensors accumulate radiation damage.

Results inform sensor performance and longevity predictions.

Abstract

After ten years of operation at the LHC, the planar pixel sensors of the innermost barrel layer of the ATLAS Pixel detector have accumulated an average bulk damage fluence in excess of $2\times10^{15}$ 1 MeV-neutrons equivalent/cm$^2$. The macroscopic effects of this radiation are an increase of the sensor leakage current, a loss of charge collection efficiency and an increase of the depletion voltage. Using regular bias voltage scans performed at the beginning and end of each data taking campaign the evolution of the pixel cluster charge and bulk depletion is studied as a function of particle fluence. Results are interpreted with the modelling provided by standalone TCAD and ATLAS Monte Carlo simulation including radiation damage effects. The dependence of the collected charge and the depletion voltage with integrated luminosity are studied through the full period of operation.