Pixel Vertex Detector Research Articles

Ultra-high-granularity detector simulation with intra-event aware generative adversarial network and self-supervised relational reasoning

Simulating high-resolution detector responses is a computationally intensive process that has long been challenging in Particle Physics. Despite the ability of generative models to streamline it, full ultra-high-granularity detector simulation still proves to be difficult as it contains correlated and fine-grained information. To overcome these limitations, we propose Intra-Event Aware Generative Adversarial Network (IEA-GAN). IEA-GAN presents a Transformer-based Relational Reasoning Module that approximates an event in detector simulation, generating contextualized high-resolution full detector responses with a proper relational inductive bias. IEA-GAN also introduces a Self-Supervised intra-event aware loss and Uniformity loss, significantly enhancing sample fidelity and diversity. We demonstrate IEA-GAN’s application in generating sensor-dependent images for the ultra-high-granularity Pixel Vertex Detector (PXD), with more than 7.5 M information channels at the Belle II Experiment. Applications of this work span from Foundation Models for high-granularity detector simulation, such as at the HL-LHC (High Luminosity LHC), to simulation-based inference and fine-grained density estimation.

The LHCb Upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software.

Upgrade of Belle II vertex detector with CMOS pixel technology

The Belle II experiment at KEK in Japan considers upgrading its vertex detector system to address the challenges posed by high background levels caused by the increased luminosity of the SuperKEKB collider. One proposal for upgrading the vertex detector aims to install a 5-layer all monolithic pixel vertex detector based on fully depleted CMOS sensors in 2027. The new system will use the OBELIX MAPS chips to improve background robustness and reduce occupancy levels through small and fast pixels. This causes better track finding, especially for low transverse momenta tracks. This text will focus on the predecessor of the OBELIX sensor, the TJ-Monopix2, presenting laboratory and test beam results on pixel response, efficiency, and spatial resolution.

Simulation of an all-layer monolithic pixel vertex detector for the Belle II upgrade

The Belle II experiment is evaluating an upgrade program aiming at the time frame 2026–2027 for the installation of the upgraded detectors, to improve the detector performance and robustness against beam-induced backgrounds. The VTX concept, a fully-pixelated system based on depleted monolithic active pixel sensors, has been developed as a replacement of the current pixel-and-strip vertex detector. A simulation framework for the VTX has been developed and integrated with the standard Belle II simulation, facilitating the comparison among different layouts. Simulation results (such as tracking efficiency and vertex resolution) on benchmark physics channels are presented, showing a significant improvement with respect to the current detector.

Pixel Detector Background Generation using Generative Adversarial Networks at Belle II

The pixel vertex detector (PXD) is an essential part of the Belle II detector recording particle positions. Data from the PXD and other sensors allow us to reconstruct particle tracks and decay vertices. The effiect of background hits on track reconstruction is simulated by adding measured or simulated background hit patterns to the hits produced by simulated signal particles. This model requires a large set of statistically independent PXD background noise samples to avoid a systematic bias of reconstructed tracks. However, data from the fine-grained PXD requires a substantial amount of storage. As an efficient way of producing background noise, we explore the idea of an on-demand PXD background generator using conditional Generative Adversarial Networks (GANs), adapted by the number of PXD sensors in order to both increase the image fidelity and produce sensor-dependent PXD hitmaps.

Simultaneous Global and Local Alignment of the Belle II Tracking Detectors

The alignment of the Belle II tracking system, composed of a pixel and strip vertex detectors and central drift chamber, is described by approximately sixty thousand parameters; from local alignment of sensors and wires to relative global alignment of the sub-detectors. In the next data reprocessing, scheduled since Spring 2021, we aim to determine all parameters in a simultaneous fit by Millepede II, where recent developments allow to achieve a direct solution of the full problem in about one hour and make it practically feasible for regular detector alignment. The tracking detectors and the alignment technique are described and the alignment strategy is discussed in the context of studies on simulations and experience obtained from recorded data. Preliminary results and further refinements based on studies of real Belle II data are presented.

New pixel detector concept DuTiP for Belle II upgrade and the ILC with an SOI technology

Belle II detector upgrade is being discussed aiming to collect five times larger integrated luminosity of 250 ab−1. The beam background level is expected five times higher than current design, thus a new pixel vertex detector with faster readout should be developed. We have invented a new pixel detector concept DuTiP for the Belle II upgrade which can be also used for the International Linear Collider (ILC) with small modifications. To realize the DuTiP concept, an SOI technology is chosen as a baseline with a pixel size of 35μm×35μm. The DuTiP concept and its application to a monolithic pixel detector in an SOI technology are explained.

Generation of Belle II Pixel Detector Background Data with a GAN

To match the statistical precision due to the large dataset that Belle II is expected to collect, simulations that accurately describe real data are required. The effect of beam background must be considered and can be taken into account with overlaying random trigger data, but its large size is a technical challenge. This problem can be mitigated by generating beam background data with generative adversarial networks. A proof of principle is shown for the background data recorded by the pixel vertex detector.

MAPS application in the STAR and ALICE Experiments

Abstract Monolithic Active Pixel Sensors (MAPS) offer a set of highly desirable characteristics for high precision tracking of charged particles. These characteristics include relatively high readout speed, low mass and radiation length, low power dissipation and cost and complexity savings over hybrid detectors. These features along with reasonable radiation tolerance make them ideal candidates for the current heavy ion experiments at colliders. We will describe the principles of operation and the design and performance of the MAPS used in the Soleniodal Tracker at RHIC (STAR) PiXeL (PXL) vertex detector and the A Large Ion Collider Experiment (ALICE) Inner Tracking System (ITS) upgrade. In addition, we will show that the performance at STAR demonstrates the value of the technology. We will also give the performance that is expected to be achieved with the ITS upgrade at the ALICE detector at the CERN.

Search for Highly Ionizing Particles with the Pixel Detector at Belle II

The Belle II experiment, located at the SuperKEKB collider at the high-energy research facility KEK in Tsukuba, Japan, started operation in 2018. Compared to the predecessor experiment Belle, Belle II plans to increase the peak luminosity by a factor of about 40, by employing nano-beam technology in the interaction region. In particular the new, innermost sub-detector of Belle II the Pixel Vertex Detector (PXD) - is in close proximity to the interaction point. This allows for the detection of particles, which do not leave a signal in the outer sub-detectors. Among these, Highly Ionizing Particles (HIPs) encounter a characteristically high energy loss, limiting their penetration depth into the detector. Anti-deuterons and magnetic monopoles as possible HIPs are considered. Without a signal in the outer sub-detectors, no track trigger is issued, resulting in possible information loss. The possibility of identifying HIPs solely with information provided by the PXD is presented, by using neural network algorithms operating in a multidimensional parameter space of PXD cluster data.

Impact of the Belle II pixel detector on the analysis of CP-violation

The new asymmetric electron positron collider SuperKEKB in Tsukuba, Japan, is currently being commissioned. With a design luminosity of 8 · 1035 cm−2 s−1, leading ultimately to an integrated luminosity of about 50 ab−1, it will overtake by almost two orders of magnitude the record integrated luminosity reached by its predecessor KEKB. With the upgrade, the beam energy asymmetry will be reduced resulting in a lower boost. Thus, the increase in luminosity and the reduction of the boost set stringent requirements on the performance of the Belle II detector, currently under construction, in order to cope with the expected large physics rates. Consisting of two layers mounted at 14 mm and 22 mm radius from the interaction point, the new Belle II pixel vertex detector based on DEPFET technology will provide the necessary three dimensional high precision position measurements of the trajectories of charged particles. This will allow the precise reconstruction of short lived particle vertices. The physics performance of the Belle II pixel vertex detector and its impact in the reduction of experimental uncertainties will be discussed focusing on the measurement of the CP-violating parameters in B-meson decay.

Physics benchmarks for the Belle II pixel detector

SuperKEKB, the massive upgrade of the asymmetric electron positron collider KEKB in Tsukuba, Japan, aims at an integrated luminosity in excess of 50 ab−1. It will deliver an instantaneous luminosity of 8 ⋅ 1035 cm−2s−1, which is 40 times higher than the world record set by KEKB. At this high luminosity, a large increase of the background relative to the previous KEKB machine is expected. This and the more demanding physics rate ask for an entirely new tracking system. The expected increase of background would in fact create an unacceptable high occupancy for a silicon strip detector, making an efficient tracks reconstruction and vertexing impossible. The solution for Belle II is a pixel detector which intrinsically provides three dimensional space points.The new two layers silicon pixel vertex detector, based on DEPFET technology, will be mounted directly on the beam pipe. It will provide an accurate measurement of the tracks position in order to precisely reconstruct the decay vertex of the short living particles.In this paper we will discuss the physics performance of the Belle II pixel vertex detector which will be essential for the precise measurement of the CP parameters in various B and D decay modes.

Some aspects of the Pixel Vertex Detector (PXD) at Belle II

The innermost detector of the Belle II experiment makes use of the DEPFET technology. It will provide an accurate measurement of the track positions in order to reconstruct the decay vertex of the short living particles. This DEPFET technology combines signal detection and amplification in a single silicon pixel structure, so that the position measurement of traversing particles can be achieved with an overall material budget of 0.2% radiation length, corresponding to 75 μ m in order to minimize the impact of multiple scattering for low transverse momentum tracking. Moreover, the DEPEFT detector has an excellent signal-to-noise ratio, low power consumption and offers a non-destructive readout.The instantaneous luminosity of 8 × 1035 cm−2s−1 expected at SuperKEKB causes large background. The close proximity of the pixel detector to the beampipe (only 1.4 cm from the interaction point) poses many challenges to the detector technology, in particular to radiation hardness and readout speed.The vertex pixel detector consists of two DEPFET layers at radii 14 mm and 22 mm. These are 20 ladders in total corresponding to 8 megapixels (pixel sizes: (55, 60, 70, 85) × 50 μ m2). The four-fold readout in rolling shutter mode results in a total readout time of about 20 μ s for an entire frame. The concept of the sensor and the surrounding readout electronics will be presented in detail with focus on the Belle II experiment. 17 institutes from Europe and Asia work together in the DEPFET collaboration to meet these challenges.

Track reconstruction at the ILC: the ILD tracking software

One of the key requirements for Higgs physics at the International Linear Collider ILC is excellent track reconstruction with very good momentum and impact parameter resolution. ILD is one of the two detector concepts at the ILC. Its central tracking system comprises of an outer Si-tracker, a highly granular TPC, an intermediate silicon tracker and a pixel vertex detector, and it is complemented by silicon tracking disks in the forward direction. Large hit densities from beam induced coherent electron-positron pairs at the ILC pose an additional challenge to the pattern recognition algorithms. We present the recently developed new ILD tracking software, the pattern recognition algorithms that are using clustering techniques, Cellular Automatons and Kalman filter based track extrapolation. The performance of the ILD tracking system is evaluated using a detailed simulation including dead material, gaps and imperfections.

Recent achievements of the ATLAS upgrade Planar Pixel Sensors R&D project

The ATLAS upgrade Planar Pixel Sensors (PPS) project aims to prove the suitability of silicon detectors processed with planar technology to equip all layers of the pixel vertex detector proposed for the upgrade of the ATLAS experiment for the future High Luminosity LHC at CERN (HL-LHC). The detectors need to be radiation tolerant to the extreme fluences expected to be received during the experimental lifetime, with optimised geometry for full coverage and high granularity and affordable in term of cost, due to the relatively large area of the upgraded ATLAS detector system. Here several solutions for the detector geometry and results with radiation hard technologies (n-in-n, n-in-p) are discussed.

Belle2Link: A Global Data Readout and Transmission for Belle II Experiment at KEK

Abstract The Belle II experiment is an upgrade of the Belle experiment at KEK B-Factory, which will be also upgraded to SuperKEKB with a luminosity of 8 x 1035 cm-2 s-1. Belle II will be composed of new detector components: a new pixel vertex detector (PXD), a significantly larger silicon vertex detector (SVD), new design of central drift chamber (CDC), new particle identification (PID) detector, an improved electromagnetic calorimeter (ECL), higher rate KL and muon detector (KLM), and also a completely new trigger (TRG) and data acquisition systems (DAQ) to handle data produced in a 40 times higher rate. The collaboration has decided to use serial data transmission and unified readout techniques to reach simple, reliable connections between Front-End Electronics (FEE) and DAQ system with easy maintenance. A so-called Belle2Link - a unified readout and high speed data transmission has been designed for use both in the FEE of all sub-detector systems and in DAQ system. Proto-types of key modules for a HS link with 3.125Gbps line rate and

The Silicon Detector Concept

Abstract The Silicon Detector (SiD) is a collider detector concept based on all-silicon tracking and a silicon-tungsten sampling calorimeter, complemented by a powerful silicon pixel vertex detector, a hadronic calorimeter contained within the solenoidal magnet and an instrumented flux return functioning as the muon system. Optimized forward detectors are deployed to ensure hermiticity and provide luminosity measurements. In order to meet the International Linear Collider (ILC) physics goals, we have designed a general purpose detector taking full advantage of the silicon technology. The silicon detector is performant, robust against machine-induced background and, by now, a mature concept.

The FIRST experiment: interaction region and MAPS vertex detector

The improvement of the precision of the measurement of the nuclear cross-section, in order to fulfill the requirements of the actual Monte Carlo simulations for hadrontherapy and space radioprotection, is the main goal of the FIRST experiment. After a brief introduction on the treatment planning in hadrontherapy, this paper describes main characteristics and components of the experiment. The features of the interaction region detectors and their main needs (low material budget, high angular coverage, two tracks resolution and large trigger rate) are discussed. Special emphasis is devoted in discussing the new silicon pixel vertex detector, in particular its new developed data acquisition and its characterization with the first test results obtained with a prototype of the detector.

Design study for a next generation B factory pixel vertex detector

We present a conceptual design for a low-mass, all-pixel vertex detector using the CMOS quadruple well INMAPS process, capable of working in the very high luminosities exceeding 10 36 cm −2 s −1 that can be expected at the next generation e +e − B Factories. We concentrate on the vertexing requirements necessary for time-dependent measurements that are also relevant to searches for new physics beyond the Standard Model. We investigate different configurations and compare with the existing baseline designs for the Super B and B aB ar experiments.

A 256 channel 8-Bit current digitizer ASIC for the Belle-II PXD

The international DEPFET collaboration is developing a silicon pixel vertex detector (PXD), based on monolithic arrays of DEPFET transistors, for the future physics experiment Belle-II at the SuperKEKB particle accelerator in Japan. The matrix elements are read out in a 'rolling shutter mode', i.e. rows are selected consecutively and all columns are read out in each cycle of < 100 ns.One of the major parts in the front-end electronics chain is the DEPFET Current Digitizer ASIC (DCDB). It is now in a close-to-final state. The chip provides 256 channels of analog-to-digital converters with a resolution of six to eight bits. Each converter features an individual dynamic offset correction circuit as well as programmable gain and bandwidth. Several operation modes using single sampling or double correlated sampling are possible.A large synthesized digital block is used for decoding and derandomization of the conversion results. The data is put out on eight 8-bit links, operating at a speed of 400 MHz. Additionally, a JTAG compatible interface is implemented for configuration and debugging purpose.Significant effort was made to reduce the power consumption of the DCDB, since both, voltage drop on the internal power buses and heat sources in the Belle-II experiment are a concern.The chip was realized on a 3.2mm × 5mm die using the UMC 180nm CMOS technology in a multi-project wafer run, provided by EuroPractice. An extra redistribution metal layer with bump bond pads is used, allowing for flipping the chip onto the final all-silicon DEPFET sensor module.Several tests have been performed in order to prove the chip's operation and its quality in terms of noise. The results are presented.