Patrick Asenov

The DC-coupled Resistive Silicon Detectors (DC-RSD) are the evolution of the AC-coupled RSD (RSD) design, both based on the Low-Gain Avalanche Diode (LGAD) technology. The DC-RSD design concept intends to address a few known issues present in RSDs (e.g., baseline fluctuation, long tail-bipolar signals) while maintaining their advantages (e.g., signal spreading, 100% fill factor). The simulation of DC-RSD presents several unique challenges linked to the complex nature of its design and the large pixel size. The defining feature of DC-RSD, charge sharing over distances that can be as large as a millimetre, represents a formidable challenge for Technology-CAD (TCAD), the standard simulation tool. To circumvent this problem, we have developed a mixed-mode approach to the DC-RSD simulation, which exploits a combination of two simulation tools: TCAD and Spice. Thanks to this hybrid approach, it has been possible to demonstrate that, according to the simulation, the key features of the RSD, excellent timing and spatial resolutions (few tens of picoseconds and few microns), are maintained in the DC-RSD design. In this work, we present the developed models and methodology, mainly showing the results of device-level numerical simulation, which have been obtained with the state-of-the-art Synopsys Sentaurus TCAD suite of tools. Such results will provide all the necessary information for the first batch of DC-RSD produced by Fondazione Bruno Kessler (FBK) foundry in Trento, Italy.

The simulation of high-energy physics collision events is a key element for data analysis at present and future particle accelerators. The comparison of simulation predictions to data allows looking for rare deviations that can be due to new phenomena not previously observed. We show that novel machine learning algorithms, specifically Normalizing Flows and Flow Matching, can be used to replicate accurate simulations from traditional approaches with several orders of magnitude of speed-up. The classical simulation chain starts from a physics process of interest, computes energy deposits of particles and electronics response, and finally employs the same reconstruction algorithms used for data. Eventually, the data are reduced to some high-level analysis format. Instead, we propose an end-to-end approach, simulating the final data format directly from physical generator inputs, skipping any intermediate steps. We use particle jets simulation as a benchmark for comparing both discrete and continuous Normalizing Flows models. The models are validated across a variety of metrics to identify the most accurate. We discuss the scaling of performance with the increase in training data, as well as the generalization power of these models on physical processes different from the training one. We investigate sampling multiple times from the same physical generator inputs, a procedure we name oversampling, and we show that it can effectively reduce the statistical uncertainties of a dataset. This class of ML algorithms is found to be capable of learning the expected detector response independently of the physical input process. Their speed and accuracy, coupled with the stability of the training procedure, make them a compelling tool for the needs of current and future experiments.

Abstract In this work, the results of Technology-CAD (TCAD) device-level simulations of non-irradiated and irradiated Low-Gain Avalanche Diode (LGAD) detectors and their validation against experimental data will be presented. Thanks to the intrinsic multiplication of the charge within these silicon sensors, it is possible to improve the signal to noise ratio thus limiting its drastic reduction with fluence, as it happens instead for standard silicon detectors. Therefore, special attention has been devoted to the choice of the avalanche model, which allows the simulation findings to better fit with experimental data. Moreover, a radiation damage model (called “New University of Perugia TCAD model”) has been fully implemented within the simulation environment, to have a predictive insight into the electrical behavior and the charge collection properties of the LGAD detectors, up to the highest particle fluences expected in the future High Energy Physics (HEP) experiments. This numerical model allows to consider the comprehensive bulk and surface damage effects induced by radiation on silicon sensors. By coupling the “New University of Perugia TCAD model” with an analytical model that describes the mechanism of acceptor removal in the multiplication layer, it has been possible to reproduce experimental data with high accuracy, demonstrating the reliability of the simulation framework.

Abstract The next generation of high-energy physics experiments at future hadronic colliders will require tracking detectors able to efficiently operate in extreme radiation environments, where expected fluences will exceed 1 × 10 17 n eq /cm 2 . This new operating scenario imposes many efforts on the design of effective and radiation-resistant particle detectors. Low-Gain Avalanche Diode (LGAD) represents a remarkable advance because the radiation damage effects can be mitigated by exploiting its charge multiplication mechanism after heavy irradiation. To obtain the desired gain (about 10–20) on the sensor output signal, a careful implementation of the “multiplication” region is needed (i.e. the high-field junction implant). Moreover, a proper design of the peripheral region (namely, the guard-ring structure) is crucial to prevent premature breakdown and large leakage currents at very high fluences, when the bias voltage applied creates an electric field higher than 15 V/μm. In this contribution, the design of LGAD sensors for extreme fluence applications is discussed, addressing the critical technological aspects such as the choice of the active substrate thickness, the gain layer design and the optimization of the sensor periphery. The impact of several design strategies is evaluated with the aid of Technology-CAD (TCAD) simulations based on a recently proposed model for the numerical simulation of radiation damage effects on LGAD devices.

In this contribution, we present an innovative design of the Low-Gain Avalanche Diode (LGAD) gain layer, the p+ implant responsible for the local and controlled signal multiplication. In the standard LGAD design, the gain layer is obtained by implanting ∼5E16/cm3 atoms of an acceptor material, typically Boron or Gallium, in the region below the n++ electrode. In our design, we aim at designing a gain layer resulting from the overlap of a p+ and an n+ implants: the difference between acceptor and donor doping will result in an effective concentration of about 5E16/cm3, similar to standard LGADs. At present, the gain mechanism of LGAD sensors under irradiation is maintained up to a fluence of ∼1–2E15/cm2, and then it is lost due to the acceptor removal mechanism. The new design will be more resilient to radiation, as both acceptor and donor atoms will undergo removal with irradiation, but their difference will maintain constant. The compensated design will empower the 4D tracking ability typical of the LGAD sensors well above 1E16/cm2.

The MIUR PRIN 4DInSiDe collaboration aims at developing the next generation of 4D (i.e., position and time) silicon detectors based on Low-Gain Avalanche Diodes (LGAD) that guarantee to operate efficiently in the future high-energy physics experiments. To this purpose, different areas of research have been identified, involving the development, design, fabrication and test of radiation-hard devices. This research has been enabled thanks to ad-hoc advanced TCAD modelling of LGAD devices, accounting for both technological issues as well as physical aspects, e.g. different avalanche generation models and combined surface and bulk radiation damage effects modelling. In this contribution, it is reviewed the progress and the relevant detector developments obtained during the research activities in the framework of the 4DInSiDe project. • TCAD modelling for the design of radiation-hard LGAD sensors for 4D tracking. • Gain layer compensation, (p ＋ - and n ＋ -doping) to preserve the gain at high fluences. • New design approach to resistive read-out sensors: DC-coupled RSD. • DC-RSD employs a direct coupling of the resistive layer to the read-out pads. • DC-coupled low resistivity strips between read-out pads to improve the resolution.

During the era of the High Luminosity LHC (HL-LHC) the devices in its experiments will be subjected to increased radiation levels with high fluxes of neutrons and charged hadrons, especially in the inner detectors. A systematic program of radiation tests with neutrons and charged hadrons is being carried out by the CMS and ATLAS Collaborations in view of the upgrade of the experiments, in order to cope with the higher luminosity at HL-LHC and the associated increase in the pile-up events and radiation fluxes. In this work, results from a complementary radiation study with $^{60}$Co-$\gamma$ photons are presented. The doses are equivalent to those that the outer layers of the silicon tracker systems of the two big LHC experiments will be subjected to. The devices in this study are float-zone oxygenated p-type MOS capacitors. The results of CV measurements on these devices are presented as a function of the total absorbed radiation dose following a specific annealing protocol. The measurements are compared with the results of a TCAD simulation.

The “Perugia Surface and Bulk” radiation damage model is a Synopsys Sentaurus Technology CAD (TCAD) numerical model which accounts for surface and bulk damage effects induced by radiation on silicon particle detectors. In this work, the significance of the input parameters of the model, such as electron/hole cross sections and acceptor/donor introduction rates is investigated, with respect to the changes in leakage current, full depletion voltage, charge collection efficiency and the current-related damage factor α (an irradiated device’s figure of merit) of a PIN diode. Different types (IV, 1/C2-V) of comparisons are made between simulation outputs and experimental data taken from irradiated PIN diodes. Finally, the possibility of the analytical model’s validation with the examination of the Low-Gain Avalanche Detector (LGAD) case, and its general application for future silicon sensors is discussed.

The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the current instantaneous luminosity by a factor of 5 to 7, providing the opportunity to study rare processes and measure precisely the standard model parameters. To cope with the increase in pile-up (up to 200), particle density and radiation, CMS will build new silicon tracking devices with higher granularity (to reduce occupancy) and improved radiation hardness. During the R&D period tests performed under beam are a powerful way to develop and examine the behavior of silicon sensors in realistic conditions. The telescopes used up to now have a slow readout (less than 10 kHz) for the needs of the CMS experiment, since the new outer-tracker modules have an effective return-to-zero time of 25 ns (corresponding to a 40 MHz frequency) and a trigger rate of 750 kHz. In order to test the CMS Tracker modules under the LHC nominal rate, a pixel telescope named CHROMIE (CMS High Rate telescOpe MachInE) is designed, built and commissioned at CERN for beam tests with prototype modules for the CMS Phase-2 Tracker upgrade. In this article the design of CHROMIE, the calibration of its modules, and its timing and synchronization aspects are presented, along with the first beam test results. In addition, the tracking algorithm developed for CHROMIE and a preliminary Geant4 simulation study of the telescope under beam are discussed.

We have developed a software for fast calculation of capacitances in planar silicon pixel and strip sensors, based on 3D and 2D numerical solutions of the Laplace's equation. The validity of the 2D calculations was checked with capacitances measurements on Multi-Geometry Silicon Strip Detectors (MSSD). The 3D calculations were tested by comparison with pixel sensors capacitance measurements from literature. In both cases the Laplace equation results were compared with simulations obtained from the TCAD Sentaurus suite. The developed software is a useful tool for fast estimation of interstrip, interpixel and backplane capacitances, saving computation time, as a first approximation before using a more sophisticated platform for more accurate results if needed.

MUonE is a proposed experiment which aims at an independent and precise determination of the leading hadronic contribution to the muon $g-2$, based on the measurement of the hadronic running of the electromagnetic coupling in the space-like region. This can be achieved by measuring with extremely high accuracy the shape of the differential cross section of the $\mu e$ elastic scattering, using a 160$\,$GeV muon beam available at CERN, off atomic electrons of a light target. Geant4 simulations are required in order to estimate the backgrounds in the proposed experiment. For this reason, the MUonE setup has been simulated with the recent Geant4 versions containing relevant updates, mostly regarding the correct estimation of the angular distribution of the $e^{+}e^{-}$ production from muon interactions. In this work, two related studies utilizing the most accurate Geant4 physics list are presented, one involving standalone simulation tests and another one employing simulation and reconstruction using the new FairRoot release. In both cases, the latest Geant4 version has been validated comparing it with a previous version.

During the era of the High Luminosity LHC (HL-LHC) the devices in the experiments will be subjected to increased radiation levels with fluxes of neutrons and charged hadrons in the inner detectors reaching up to approximately 2.3 × 10 16 n eq /cm 2 and total ionization doses up to around 1.2 Grad.A systematic program of radiation tests with neutrons and charged hadrons is being carried out by the CMS and ATLAS Collaborations in order to cope with the higher luminosity of HL-LHC and the associated increase in the pile-up events and radiation fluxes.In this work, results from a complementary radiation study with 60 Co-γ photons are presented.The doses are equivalent to those that the outer layers of the silicon tracker systems of the two experiments will be subjected to.The devices in this study are p-type diodes and MOS capacitors.

In this work the results obtained with a calculation, in lower order, of backplane and interstrip capacitances in planar silicon microstrip sensors is presented. The method is based on a numerical solution of the 2D Laplace equation by partitioning the device in one dimension while keeping the other dimension continuous. The validity of the two-dimensional algorithm is checked through a comparison with experimental measurements and TCAD simulation performed on Multi Geometry Strip Sensors (MSSD).