Total ionizing dose measurement of the Belle II pixel detector

Sumitted to PubDB: 2026-07-07

Category: Master Thesis

Tags: PXD

Principal Authors Yannik Buch
Date 2022-10-17
Belle II Number BELLE2-MTHESIS-2026-052
Abstract The Belle II detector system at the SuperKEKB particle collider at KEK in Tsukuba, Japan, provides precision physics measurements, testing the Standard Model and searching for new physics. The innermost detector system of Belle II is a 6-layer vertex detector. The pixel detector (PXD) comprises the first two layers, that are at a distance of 14 mm and 22 mm from the interaction point, respectively. The very thin, high resolution PXD is based on DEPleted Field Effect Transistors (DEPFET). Since the beginning of the operation of the PXD 3 years ago, in 2019, the PXD is exposed to large amounts of radiation from the beam background. In this work, the ionizing dose rate received by each PXD module is measured. This is the first measurement of the ionizing dose rate of the PXD modules for their entire time of operation until the start of the long shutdown 1. The measurement uses the measured online module occupancies, that are saved as diagnostic variables by the Belle II slow control system EPICS as 1 Hz time series. The measured online occupancies are modeled using a heuristic background function, that describes the beam background composition. The considered beam background components are beam-gas, Touschek and injection backgrounds for the low energy positron ring and the high energy electron ring as well as luminosity backgrounds. Modeling the module occupancies allows for measuring the deposited ionizing dose even when the PXD is not recording data by extrapolating the model. The measurement approach and the resulting ionizing dose rate time series are presented.
Institute Goettingen

Files