Development of a Laboratory Readout System for DEPFET Pixel Detector Modules and Investigation of Radiation Backgrounds at the SuperKEKB Accelerator

With the upgrade from the e^+ e^- -collider KEKB to SuperKEKB, a 40-fold increase in instantaneous luminosity is targeted posing new challenges for the Belle II detector. Particularly the innermost detector layers, consisting of a silicon strip and Depleted P-channel Field-Effect Transistor (DEPFET) based pixel detector, operate in an environment of high event rates and increased background radiation. In the first part of this thesis, the measurements of the FANGS detector are presented, which was one of five dedicated background monitors for the commissioning phase BEAST II of the SuperKEKB accelerator. Consisting of ATLAS hybrid pixel detector modules, the detector is suitable for studies under high radiation and particle rate especially caused by synchrotron radiation. The benefit of highly segmented sensors enables the spatial measurement of radiation present close to the interaction point. Furthermore, the capability of energy resolution using a precise charge measurement method is demonstrated. The second part deals with the development of the BDAQ-PXD readout system for single DEPFET pixel detector modules which are successfully operated in the innermost layers of Belle II. BDAQ-PXD is intended to be an easily accessible and adjustable laboratory test system for irradiation and test beam environments using the custom designed BDAQ53 readout board. The implementations of FPGA firmware, software and first measurements are presented. Within the scope of this work, the DEPFET sensor properties are investigated, e.g. hit-detection efficiencies and the influence of biasing voltages on charge collection. Specifically, a hit-detection efficiency of above 99.7% is measured confirming the functionality of the BDAQ-PXD system

Status of the BELLE II Pixel Detector

The Belle II experiment at the super KEK B-factory (SuperKEKB) in Tsukuba, Japan, has been collecting $e^+e^−$ collision data since March 2019. Operating at a record-breaking luminosity of up to $4.7×10^{34} cm^{−2}s^{−1}$, data corresponding to $424 fb^{−1}$ has since been recorded. The Belle II VerteX Detector (VXD) is central to the Belle II detector and its physics program and plays a crucial role in reconstructing precise primary and decay vertices. It consists of the outer 4-layer Silicon Vertex Detector (SVD) using double sided silicon strips and the inner two-layer PiXel Detector (PXD) based on the Depleted P-channel Field Effect Transistor (DePFET) technology. The PXD DePFET structure combines signal generation and amplification within pixels with a minimum pitch of $(50×55) μm^2$. A high gain and a high signal-to-noise ratio allow thinning the pixels to $75 μm$ while retaining a high pixel hit efficiency of about $99$. As a consequence, also the material budget of the full detector is kept low at $≈0.21$$\frac{X}{X_0}$ per layer in the acceptance region. This also includes contributions from the control, Analog-to-Digital Converter (ADC), and data processing Application Specific Integrated Circuits (ASICs) as well as from cooling and support structures. This article will present the experience gained from four years of operating PXD; the first full scale detector employing the DePFET technology in High Energy Physics. Overall, the PXD has met the expectations. Operating in the intense SuperKEKB environment poses many challenges that will also be discussed. The current PXD system remains incomplete with only 20 out of 40 modules having been installed. A full replacement has been constructed and is currently in its final testing stage before it will be installed into Belle II during the ongoing long shutdown that will last throughout 2023

Effects of gamma irradiation on DEPFET pixel sensors for the Belle II experiment

For the Belle II experiment at KEK (Tsukuba, Japan) the KEKB accelerator was upgraded to deliver a 40 times larger instantaneous luminosity than before, which requires an increased radiation hardness of the detector components. As the innermost part of the Belle II detector, the pixel detector (PXD), based on DEPFET (DEpleted P-channel Field Effect Transistor) technology, is most exposed to radiation from the accelerator. An irradiation campaign was performed to verify that the PXD can cope with the expected amount of radiation. We present the results of this measurement campaign in which an X-ray machine was used to irradiate a single PXD half-ladder to a total dose of 266 kGy. The half-ladder is from the same batch as the half-ladders used for Belle II. According to simulations, the total accumulated dose corresponds to 7–10 years of Belle II operation. While individual components have been irradiated before, this campaign is the first full system irradiation. We discuss the effects on the DEPFET sensors, as well as the performance of the front-end electronics. In addition, we present efficiency studies of the half-ladder from beam tests performed before and after the irradiation

Impacts of Demographic Trends on US Household Size and Structure

We use a household projection model to construct future scenarios for the United States designed to reflect a wide but plausible range of outcomes, including a new set of scenarios for union formation and dissolution rates based on past trends, experience in other countries, and current theory. The period covered is from 2000 to 2100. We find that the percentage of people living in households headed by the elderly may climb from 11 percent in 2000 to 20-31 percent in 2050 and 20-39 percent in 2100, while the average size of households could plausibly be as low as 2.0 or as high as 3.1 by the second half of the century. We assess the sensitivity of household size and structure to various demographic events, and show that outcomes are most sensitive to changes in fertility rates and rates of union formation and dissolution. They are less sensitive to the timing of marriage and childbearing and to changes in life expectancy. Copyright 2007 The Population Council, Inc..

EUDAQ—a data acquisition software framework for common beam telescopes

EUDAQ is a generic data acquisition software developed for use in conjunction with common beam telescopes at charged particle beam lines. Providing high-precision reference tracks for performance studies of new sensors, beam telescopes are essential for the research and development towards future detectors for high-energy physics. As beam time is a highly limited resource, EUDAQ has been designed with reliability and ease-of-use in mind. It enables flexible integration of different independent devices under test via their specific data acquisition systems into a top-level framework. EUDAQ controls all components globally, handles the data flow centrally and synchronises and records the data streams. Over the past decade, EUDAQ has been deployed as part of a wide range of successful test beam campaigns and detector development applications

Measurements of Beam Backgrounds in SuperKEKB Phase 2

The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for ward and conclude it is safe to install the Belle II vertex detector