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Geant4 simulation of transition radiation detector based on DEPFET silicon pixel matrices
Abstract
This paper presents new developments in Monte Carlo simulation for test beam measurements of a silicon transition radiation detector based on DEPFET—a silicon active pixel detector. The test of DEPFET with fiber radiator has been carried out at the DESY 5 GeV electron beam. Monte Carlo simulation of the test beam setup is based on Geant4. A comparison of Geant4 simulation with test beam data is presented.
... For multiple interfaces, interference effects may lead to an increase of the number of maxima and even to a change of the position of the most probable angle, and remove the strong dependence on the -factor. Previous attempts to measure the TR angular distribution were not fully successful because of the limited functionalities of the setups [6][7][8]. In this work, for the first time high precision simultaneous measurements of the TR photon energy and its production angle have been performed. ...
X-ray Transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. Particle identification is often achieved based on a threshold effect of the X-ray transition radiation (TR). In most of the detectors, TR emission starts at γ factors above ∼500 and reaches saturation at γ∼2−3⋅10³. However, many experiments require particle identification up to γ∼10⁵, which is difficult to achieve with current detectors, based only on the measurement of the photon energy together with the particle ionization losses. Additional information on the Lorentz factor can be extracted from the angular distribution of TR photons. TRDs based on pixel detectors give a unique opportunity for precise measurements of spectral and angular distributions of TR at the same time. A 500 μm thick silicon sensor bump bonded to a Timepix3 chip was used in a test beam measurement at the CERN SPS. A beam telescope was employed to separate clusters produced by the primary beam particles from the potential TR clusters. Spectral and angular distributions of TR were studied with high precision for the first time using beams of pions, electrons and muons at different momenta. In this paper, the measurement and analysis techniques are described, and first results are presented.
X-ray transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. In most of the detectors, emission of the X-ray transition radiation (TR) starts at Lorentz factors above γ∼500 and reaches saturation at γ∼2÷3⋅103. However, many experiments require particle identification up to γ∼105, which is very difficult to achieve with conventional detectors. Semiconductor pixel detectors offer a unique opportunity for precise simultaneous measurements of spectral and angular parameters of TR photons. Test beam studies of the energy and the angular distributions of TR photons emitted by electrons and muons of different momenta crossing several types of radiators were performed at the CERN SPS with a 480 μm thick silicon detector bonded to a Timepix3 chip. High resolution images of the energy−angle phase space of the TR produced by different radiators were obtained and compared with MC simulations. The characteristic interference patterns are in agreement with the theoretical models with an unprecedented level of details. The studies presented in this paper also show that simultaneous measurements of both the energy and the emission angles of the TR X-rays could be used to enhance the particle identification performances of TRDs.
Transition Radiation Detector based on the usage of thin scintillators (Sci-TRD) is proposed for particle identification. Such type of TRD may be especially interesting for space apparatus because of no gas. The proposed detector is based on the thin transparent films with incorporated micro-granules of Lu2SiO5:Ce scintillator. Scintillation signal produced by absorbed TR photons is registered by SiPM connected to WLS fibers. Results of measurements with samples of such films are presented. The clear signals from 55Fe (∼5keV) and 241Am (∼16keV) gamma sources were observed. The detailed Monte Carlo simulations of such kind of TRD are also presented.
DePMOS structure provides detection and amplification jointly and it is free of interconnection stray capacitance. An electrical model of the device has been provided. The most relevant parameters have been measured in order to choose an adequate readout electronics, to fully exploit the intrinsic low noise of the device. DePMOS can operate in continuous mode, i.e. without applying any clear pulse during the signal processing, and can be read out by a time continuous shaper amplifier. An unequalled noise of 2.2 electrons r.m.s. at room temperature has been measured. In this mode DePMOS can be used e.g. as the readout device for silicon drift detectors. DePMOS was developed to be the basic element of an active pixel sensor suitable to cope with the requirements of XEUS wide field imager. In a matrix arrangement, each pixel must be read out by a time variant filter. A multichannel integrated shaping amplifier, based on multi correlated double sampling, has been designed. Spectroscopic resolution obtained filtering the pixel matrix with this readout chip is in agreement with measurements in continuous mode and matches the predictions of the model presented. It has also been experimentally proved that the clear procedure doesn't introduce additional noise contribution, even in the very low noise range achieved. This qualifies DePMOS as a "reset-noise-free" device.
Transition Radiation Detectors (TRD) have the attractive feature of being able to separate particles by their gamma factor. Replacing the xenon based gaseous detectors by modern silicon detectors is complicated by the large energy losses of charged particles in 300–700μm of silicon. A silicon active pixel detector—DEPFET—has features which allows another detection technique to be used, in order to overcome the existing limitation on separating transition radiation photons with an energy loss from a charged particle in the same pixel. The tests of DEPFET with fiber radiator have been carried out at CERN SPS and DESY beams. The first results of test-beam measurements and Monte Carlo simulation are presented.
Implementation of particular C++ classes in Geant4 X-ray transition radiation (XTR) library is discussed. Recent developments concerning the transparent regular XTR radiator and XTR generated in straw tube (consisting three media) are considered in details. Simulation results are compared with experimental data.
We discuss an implementation of Photo Absorption Ionisation model describing ionisation energy loss produced by a relativistic charged particle in very thin absorbers. The implementation allows us to calculate ionisation energy losses in any material consisting of elements with atomic numbers in the range 1–100. Comparisons of simulation with the experimental data from gaseous and solid state detectors are presented.
Transition radiation detectors (TRDs) have been tested for the separation of electrons from pions in the momentum range between 1 and 6 GeV/c. Foams as well as fibres and foils served as radiator materials while two types of chambers, a longitudinal drift chamber (DC) and a multiwire proportional chamber (MWPC), both of 16 mm depth and dominantly filled with xenon, were used for detecting the transition radiation photons with a setup of four chambers. Analyzing the data we compared the methods of mean, truncated mean and of maximum likelihood of the total charge measurements and several methods of cluster analysis. As a result of the total charge measurements performed at test beams at CERN and DESY we obtained about 1% pion contamination at 90% electron efficiency for the polypropylene materials in the configuration of four modules with a total length of 40 cm. An improvement by a factor of about two for the electron/pion discrimination can be obtained in the case of a detailed analysis of the clusters.
The possibility of spatial separation of relativistic particle ionization loss and transition radiation (RTR) γ-quanta from this particle was investigated. For this aim a double electroluminescent drift chamber filled with xenon at 10 atm pressure was built. The detailed characteristics of the chamber have been investigated on the 3.5 GeV electron beam of the Serpukhov accelerator. The results show the possibility of spatial resolution of TR and ionization signals.
The DEPFET pixel detector offers first stage in-pixel amplification by incorporating a field effect transistor in the high resistivity silicon substrate. In this concept, a very small input capacitance can be realized thus allowing for low noise measurements. This makes DEPFET sensors a favorable technology for tracking in particle physics. Therefore a system with a DEPFET pixel matrix was developed to test DEPFET performance for an application as a vertex detector for the Belle II experiment. The system features a current based, row-wise readout of a DEPFET pixel matrix with a designated readout chip, steering chips for matrix control, a FPGA based data acquisition board, and a dedicated software package. The system was successfully operated in both test beam and lab environment. In 2009 new DEPFET matrices have been characterized in a 120GeV pion beam at the CERN SPS. The current status of the DEPFET system and test beam results are presented.
On the basis of the semiconductor drift chamber many new detectors are proposed, which enable the determination of energy, energy loss, position and penetration depth of radiation. A novel integrated transistor-detector configuration allows nondestructive repeated readout and amplification of the signal. The concept may be used for the construction of one-or-two-dimensional pixel arrays.
Pixel detectors, as the current technology of choice for the innermost vertex detection, have reached a stage at which large detectors have been built for the LHC experiments and a new era of developments, both for hybrid and for monolithic or semi-monolithic pixel detectors is in full swing. This is largely driven by the requirements of the upgrade programme for the superLHC and by other collider experiments which plan to use monolithic pixel detectors for the first time. A review on current pixel detector developments for particle tracking and vertexing is given, comprising hybrid pixel detectors for superLHC with its own challenges in radiation and rate, as well as on monolithic, so-called active pixel detectors, including monolithic active pixels (MAPS) and DEPFET pixels for RHIC and superBelle.
A new generation of MOS-type DEPFET active pixel sensors in double metal/double poly technology with ∼25 μm pixel size has been developed to meet the requirements of the vertex detector at the International Linear Collider (ILC). The paper presents the design and technology of the new linear MOS-type DEPFET sensors including a module concept and results of a feasibility study on how to build ultra-thin fully depleted sensors. One of the major challenges at the ILC is the dominant e+e− pair background from beam–beam interactions. The resulting high occupancy in the first layer of the vertex detector can be reduced by an extremely fast read out of the pixel arrays but the pair-produced electrons will also damage the sensor by ionization. Like all MOS devices, the DEPFET is inherently susceptible to ionizing radiation. The predominant effect of this kind of irradiation is the shift of the threshold voltage to more negative values due to the build up of positive oxide charges. The paper presents the first results of the irradiation of such devices with hard X-rays and gamma rays from a 60Co source up to 1 Mrad(Si) under various biasing conditions.
The use of transition radiation (TR) as a means of identifying high energy particles has now become a subject of intensive experimental investigations and applications. Our intention is first to study the physics of these phenomena and to describe ways of building detectors which can efficiently identify particles.