arXiv subjects

E. Garutti

Publications and source records attributed to E. Garutti.

At least 37 records · Page 2Linked to original sources

arXiv2021

Position reconstruction for segmented detectors

The topic of the paper is the position reconstruction from signals of segmented detectors. With the help of a simple simulation, it is shown that the position reconstruction using the centre-of-gravity method is strongly biased, if the width of the charge (or e.g. light) distribution at the electrodes (or photo detectors) is less than the read-out pitch. A method is proposed which removes this bias for events with signals in two or more read-out channels and thereby improves the position resolution. The method also provides an estimate of the position-response function for every event. Examples are given for which its width as a function of the reconstructed position varies by as much as an order of magnitude. A fast Monte Carlo program is described which simulates the signals from a silicon pixel detector traversed by charged particles under different angles, and the results obtained with the proposed reconstruction method and with the centre-of-gravity method are compared. The simulation includes the local energy-loss fluctuations, the position-dependent electric field, the diffusion of the charge carriers, the electronics noise and charge thresholds for clustering. A comparison to test-beam-data is used to validate the simulation.

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arXiv2021

Position resolution with 25 um pitch pixel sensors before and after irradiation

Pixelated silicon detectors are state-of-the-art technology to achieve precise tracking and vertexing at collider experiments, designed to accurately measure the hit position of incoming particles in high rate and radiation environments. The detector requirements become extremely demanding for operation at the High-Luminosity LHC, where up to 200 interactions will overlap in the same bunch crossing on top of the process of interest. Additionally, fluences up to 2.3 10^16 cm^-2 1 MeV neutron equivalent at 3.0 cm distance from the beam are expected for an integrated luminosity of 3000 fb^-1. In the last decades, the pixel pitch has constantly been reduced to cope with the experiment's needs of achieving higher position resolution and maintaining low pixel occupancy per channel. The spatial resolution improves with a decreased pixel size but it degrades with radiation damage. Therefore, prototype sensor modules for the upgrade of the experiments at the HL-LHC need to be tested after being irradiated. This paper describes position resolution measurements on planar prototype sensors with 100x25 um^2 pixels for the CMS Phase-2 Upgrade. It reviews the dependence of the position resolution on the relative inclination angle between the incoming particle trajectory and the sensor, the charge threshold applied by the readout chip, and the bias voltage. A precision setup with three parallel planes of sensors has been used to investigate the performance of sensors irradiated to fluences up to F_eq = 3.6 10^15 cm-2. The measurements were performed with a 5 GeV electron beam. A spatial resolution of 3.2 +\- 0.1 um is found for non-irradiated sensors, at the optimal angle for charge sharing. The resolution is 5.0 +/- 0.2 um for a proton-irradiated sensor at F_eq = 2.1 10^15 cm-2 and a neutron-irradiated sensor at F_eq = 3.6 10^15 cm^-2.

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arXiv2020

MADMAX Status Report

In this report we present the status of the MAgnetized Disk and Mirror Axion eXperiment (MADMAX), the first dielectric haloscope for the direct search of dark matter axions in the mass range of 40 to 400 $μ$eV. MADMAX will consist of several parallel dielectric disks, which are placed in a strong magnetic field and with adjustable separations. This setting is expected to allow for an observable emission of axion induced electromagnetic waves at a frequency between 10 and 100 GHz corresponding to the axion mass. The present document orignated from a status report to the DESY PRC in 2019.

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arXiv2020

A new experimental approach to probe QCD axion dark matter in the mass range above 40$μ$eV

The axion emerges in extensions of the Standard Model that explain the absence of CP violation in the strong interactions. Simultaneously, it can provide naturally the cold dark matter in our universe. Several searches for axions and axion-like particles (ALPs) have constrained the corresponding parameter space over the last decades but no unambiguous hints of their existence have been found. The axion mass range below 1 meV remains highly attractive and a well motivated region for dark matter axions. In this White Paper we present a description of a new experiment based on the concept of a dielectric haloscope for the direct search of dark matter axions in the mass range of 40 to 400 $μ$eV. This MAgnetized Disk and Mirror Axion eXperiment (MADMAX) will consist of several parallel dielectric disks, which are placed in a strong magnetic field and with adjustable separations. This setting is expected to allow for an observable emission of axion induced electromagnetic waves at a frequency between 10 to 100 GHz corresponding to the axion mass.

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arXiv2020

A computer program to simulate the response of SiPMs

A Monte Carlo program which simulates the response of SiPMs is presented. Input to the program are the mean number and the time distribution of Geiger discharges from light, as well as the dark-count rate. For every primary Geiger discharge from light and dark counts in an event, correlated Geiger discharges due to prompt and delayed cross-talk and after-pulses are simulated, and a table of the amplitudes and times of all Geiger discharges in a specified time window generated. A number of different physics-based models and statistical treatments for the simulation of correlated Geiger discharges can be selected. These lists for many events together with different options for the pulse shapes of single Geiger discharges are used to simulate charge spectra, as measured by a current-integrating charge-to-digital converter, or current transients convolved with an electronics response function, as recorded by a digital oscilloscope. The program can be used to compare simulations with different assumptions to experimental data, and thus find out which models are most appropriate for a given SiPM, optimise the operating conditions and readout for a given application or test programs which are used to extract SiPM parameters from experimental data.

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arXiv2019

Characterisation of different stages of hadronic showers using the CALICE Si-W ECAL physics prototype

A detailed investigation of hadronic interactions is performed using $π^-$-mesons with energies in the range 2--10 GeV incident on a high granularity silicon-tungsten electromagnetic calorimeter. The data were recorded at FNAL in 2008. The region in which the $π^-$-mesons interact with the detector material and the produced secondary particles are characterised using a novel track-finding algorithm that reconstructs tracks within hadronic showers in a calorimeter in the absence of a magnetic field. The principle of carrying out detector monitoring and calibration using secondary tracks is also demonstrated.

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arXiv2019

Analysis methods for highly radiation-damaged SiPMs

Prototype SiPMs with 4384 pixels of dimensions $15 \times 15~μ$m$^2$ produced by KETEK have been irradiated with reactor neutrons to eight fluences between $10^9$ and $5\times 10^{14}$ cm$^{-2}$. For temperatures between $-30~^\circ $C and $+30~^\circ $C capacitance-voltage, admittance-frequency, current-forward voltage, current-reverse voltage and charge-voltage measurements with and without illumination by a sub-nanosecond laser have been performed. The data have been analysed using different methods in order to extract the dependence on neutron fluence and temperature of the electrical parameters, the breakdown oltage, the activation energy for the current generation, the dark-count rate and the response to light pulses. The results from the different analysis methods are compared.

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arXiv2019

Analysis of Testbeam Data of the Highly Granular RPC-Steel CALICE Digital Hadron Calorimeter and Validation of Geant4 Monte Carlo Models

We present a study of the response of the highly granular Digital Hadronic Calorimeter with steel absorbers, the Fe-DHCAL, to positrons, muons, and pions with momenta ranging from 2 to 60 GeV/c. Developed in the context of the CALICE collaboration, this hadron calorimeter utilises Resistive Plate Chambers as active media, interspersed with steel absorber plates. With a transverse granularity of $1\,\times\,1\,$cm$^{2}$ and a longitudinal segmentation of 38 layers, the calorimeter counted 350,208 readout channels, each read out with single-bit resolution (digital readout). The data were recorded in the Fermilab test beam in 2010-11. The analysis includes measurements of the calorimeter response and the energy resolution to positrons and muons, as well as detailed studies of various shower shape quantities. The results are compared to simulations based on Geant4, which utilise different electromagnetic and hadronic physics lists.

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arXiv2018

Radiation damage of SiPMs

The current understanding of radiation tollerance of Silicon Photomultipliers (SiPMs) is reviewd. Radiation damage in silicon sensors is briefly introduced, surface and bulk effects are separately addressed. Results on the operation of irradiated SiPMs with X-ray, gamma, electron, proton and neutron sources are presented. The most critical effect of radiation on SiPMs is the increase of dark count rate, which makes it impossible to resolve signals generated by a single photon from the noise. Methods to characterize irradiated SiPMs after their single photo-electron resolution is lost are discussed. Due to the important similarity in the operation below the breakdown voltage, also older studies on radiadion damage of avalange photodiodes (APD) are reviewed. Finally, ideas are presented on how to approach the development of radiation hard SiPMs in the future.

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arXiv2018

Hadronic Energy Resolution of a Combined High Granularity Scintillator Calorimeter System

This paper presents results obtained with the combined CALICE Scintillator Electromagnetic Calorimeter, Analogue Hadronic Calorimeter and Tail Catcher & Muon Tracker, three high granularity scintillator-SiPM calorimeter prototypes. The response of the system to pions with momenta between 4 GeV/c and 32 GeV/c is analysed, including the energy response, resolution, and longitudinal shower profiles. The results of a software compensation technique based on weighting according to hit energy are compared to those of a standard linear energy reconstruction. The results are compared to predictions of the GEANT4 physics lists QGSP_BERT_HP and FTFP_BERT_HP.

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arXiv2017

Characterisation of highly radiation-damaged SiPMs using current measurements

The characterisation of radiation-damaged SiPMs is a major challenge, when the average time between dark counts approaches, or even exceeds, the signal decay time. In this note a collection of formulae is presented, which have been developed and used for the analysis of current measurements for SiPMs in the dark and illuminated by an LED, before and after hadron irradiation. It is shown, how parameters like the breakdown voltage, the quenching resistance, the dark-count rate, the reduction of the photo-detection efficiency due to dark counts and the Geiger discharge probability can be estimated from current-voltage measurements. The only additional SiPM parameters needed are the pixel capacitance, the number of pixels and the correlated noise. Central to the method is the concept of the pixel occupancy, the probability of a Geiger discharge in a single pixel during a given time interval, for which the decay time of the SiPM signal has been assumed. As an illustration the formulae are used to characterise a KETEK SiPM before and after irradiation by a fluence of 5E13 cm$^{-2}$ of reactor neutrons for temperatures of -30°C and +20°C, where dark-count rates exceeding 1E11 Hz are observed.

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arXiv2017

Neutron irradiation effect on SiPMs up to $Φ_{neq}$ = 5 $\times$ 10$^{14}$ cm$^{-2}$

Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice for increasingly more particle detection applications, from fundamental physics to medical and societal applications. One major consideration for their use at high-luminosity colliders is the radiation damage induced by hadrons, which leads to a dramatic increase of the dark count rate. KETEK SiPMs have been exposed to various fluences of reactor neutrons up to $Φ_{neq}$ = 5$\times$10$^{14}$ cm$^{-2}$ (1 MeV equivalent neutrons). Results from the I-V, and C-V measurements for temperatures between $-$30$^\circ$C and $+$30$^\circ$C are presented. We propose a new method to quantify the effect of radiation damage on the SiPM performance. Using the measured dark current the single pixel occupation probability as a function of temperature and excess voltage is determined. From the pixel occupation probability the operating conditions for given requirements can be optimized. The method is qualitatively verified using current measurements with the SiPM illuminated by blue LED light.

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arXiv2017

Test Beam Performance Measurements for the Phase I Upgrade of the CMS Pixel Detector

A new pixel detector for the CMS experiment was built in order to cope with the instantaneous luminosities anticipated for the Phase~I Upgrade of the LHC. The new CMS pixel detector provides four-hit tracking with a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and allows operation at low comparator thresholds. In this paper, comprehensive test beam studies are presented, which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency is $99.95\pm0.05\,\%$, while the intrinsic spatial resolutions are $4.80\pm0.25\,μ\mathrm{m}$ and $7.99\pm0.21\,μ\mathrm{m}$ along the $100\,μ\mathrm{m}$ and $150\,μ\mathrm{m}$ pixel pitch, respectively. The findings are compared to a detailed Monte Carlo simulation of the pixel detector and good agreement is found.

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arXiv2017

Determination of the p-spray profile for n+p silicon sensors using a MOSFET

The standard technique to electrically isolate the $n^+$ implants of segmented silicon sensors fabricated on high-ohmic $p$-type silicon are $p^+$-implants. Although the knowledge of the $p^+$-implant dose and of the doping profile is highly relevant for the understanding and optimisation of sensors, this information is usually not available from the vendors, and methods to obtain it are highly welcome. The paper presents methods to obtain this information from circular MOSFETs fabricated as test structures on the same wafer as the sensors. Two circular MOSFETs, one with and one without a $p^+$-implant under the gate, are used for this study. They were produced on Magnetic Czochralski silicon doped with $\approx 3.5 \times 10^{12}$ cm$^{-2}$ of boron and $\langle 1 0 0 \, \rangle$ crystal orientation. The drain-source current as function of gate voltage for different back-side voltages is measured at a drain-source voltage of 50 mV in the linear MOSFET region, and the values of threshold voltage and mobility extracted using the standard MOSFET formulae. To determine the bulk doping, the implantation dose and profile from the data, two methods are used, which give compatible results. The doping profile, which varies between $3.5 \times 10^{12}$ cm$^{-3}$ and $2 \times 10^{15}$ cm$^{-3}$ for the MOSFET with $p^+$-implant, is determined down to a distance of a fraction of a $μ$m from the Si-SiO$_2$ interface. The method of extracting the doping profiles is verified using data from a TCAD simulation of the two MOSFETs. The details of the methods and of the problems encountered are discussed.

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arXiv2017

On the characterisation of SiPMs from pulse-height spectra

Methods are developed, which use the pulse-height spectra of SiPMs measured in the dark and illuminated by pulsed light, to determine the pulse shape, the dark-count rate, the gain, the average number of photons initiating a Geiger discharge, the probabilities for prompt cross-talk and after-pulses, as well as the electronics noise and the gain fluctuations between and in pixels. The entire pulse-height spectra, including the background regions in-between the peaks corresponding to different number of Geiger discharges, are described by single functions. As a demonstration, the model is used to characterise a KETEK SiPM with 4382 pixels of 15 μm x 15 μm area for voltages between 2.5 and 8 V above the breakdown voltage at 20°C. The results are compared to other methods of characterising SiPMs. Finally, examples are given, how the complete description of the pulse-eight spectra can be used to optimise the operating voltage of SiPMs, and a method for an in-situ calibration and monitoring of SiPMs, suited for large-scale applications, is proposed.

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arXiv2016

Study of the breakdown voltage of SiPMs

The breakdown behaviour of SiPMs (Silicon PhotoMultiplier) with pixel sizes of 15$\times $15, 25$\times $25, 50$\times $50, and 100$\times $100 $μ$m$^2$, manufactured by KETEK, has been investigated. From the current-voltage characteristics measured with and without illumination by LED light of 470 nm wavelength, the current-breakdown voltage, $V_I$, and from linear fits of the voltage dependence of the SiPM gain, measured by recording pulse-area spectra, the gain-breakdown voltage, $V_G$, have been obtained. The voltage dependence of the Geiger-breakdown probability was determined from the fraction of zero photoelectron events with LED illumination. By comparing the results to a model calculation, the photodetection-breakdown voltage, $V_{PD}$, has been determined. Within experimental uncertainties, $V_I$ and $V_{PD}$ are equal and independent of pixel size. For $V_G$, a dependence on pixel size is observed. The difference $V_I - V_G$ is about 1 V for the SiPM with 15 $μ$m pixels, decreases with pixel size and is compatible with zero for the SiPM with 100 $μ$m pixels.

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arXiv2016

The influence of edge effects on the determination of the doping profile of silicon pad diodes

Edge effects for square p+n pad diodes with guard rings, fabricated on high-ohmic silicon, are investigated. Using capacitance-voltage measurements of two pad diodes with different areas, the planar and the edge contributions to the diode capacitance are determined separately. It is shown that the doping concentration derived from the capacitance-voltage measurements with and without edge corrections differ significantly. After the edge correction, the bulk doping of the pad diodes is found to be uniform within +/- 1.5%. The voltage dependence of the edge capacitance is compared to the predictions of two simple models.

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arXiv2016

Enabling Technologies for Silicon Microstrip Tracking Detectors at the HL-LHC

While the tracking detectors of the ATLAS and CMS experiments have shown excellent performance in Run 1 of LHC data taking, and are expected to continue to do so during LHC operation at design luminosity, both experiments will have to exchange their tracking systems when the LHC is upgraded to the high-luminosity LHC (HL-LHC) around the year 2024. The new tracking systems need to operate in an environment in which both the hit densities and the radiation damage will be about an order of magnitude higher than today. In addition, the new trackers need to contribute to the first level trigger in order to maintain a high data-taking efficiency for the interesting processes. Novel detector technologies have to be developed to meet these very challenging goals. The German groups active in the upgrades of the ATLAS and CMS tracking systems have formed a collaborative "Project on Enabling Technologies for Silicon Microstrip Tracking Detectors at the HL-LHC" (PETTL), which was supported by the Helmholtz Alliance "Physics at the Terascale" during the years 2013 and 2014. The aim of the project was to share experience and to work together on key areas of mutual interest during the R&D phase of these upgrades. The project concentrated on five areas, namely exchange of experience, radiation hardness of silicon sensors, low mass system design, automated precision assembly procedures, and irradiations. This report summarizes the main achievements.

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