# Deep Diffused Avalanche Photodiodes for Charged Particles Timing

## TL;DR

This paper investigates deep diffused Avalanche Photodiodes as potential timing detectors for HL-LHC, demonstrating their performance and radiation hardness through beam tests and irradiation studies.

## Contribution

It introduces the use of deep diffused APDs for direct charged particle timing in high-radiation environments, with comprehensive characterization and radiation damage assessment.

## Key findings

- Achieved timing resolution around 30 ps in beam tests.
- Demonstrated radiation tolerance up to $ ext{10}^{15}$ cm$^{-2}$ neutron equivalent fluence.
- Characterized signal properties and damage effects across different device sizes.

## Abstract

The upgrades of ATLAS and CMS for the High Luminosity LHC (HL-LHC) highlighted physics objects timing as a tool to resolve primary interactions within a bunch crossing. Since the expected pile-up is around 200, with an r.m.s. time spread of 180 ps, a time resolution of about 30 ps is needed. The timing detectors will experience a 1-MeV neutron equivalent fluence of about $\Phi_{eq}=10^{14}$ and $10^{15}$ cm$^{-2}$ for the barrel and end-cap regions, respectively. In this contribution, deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. To improve the detector's timing performance, the APDs are used to directly detect the traversing particles, without a radiator medium where light is produced. Devices with an active area of $8\times8$ mm$^2$ were characterized in beam tests. The timing performance and signal properties were measured as a function of position on the detector using a beam telescope and a microchannel plate photomultiplier (MCP-PMT). Devices with an active area of $2\times2$ mm$^2$ were used to determine the effects of radiation damage and characterized using a ps pulsed laser. These detectors were irradiated with neutrons up to $\Phi_{eq}=10^{15}$ cm$^{-2}$.