Minimum Ionising Particles Research Articles

CMS Upgrades with a focus on detector technologies

In 2026 the Large Hadron Collider after its upgrade will provide an instantaneous luminosity of 5÷7×1034 cm2s−1, which is three times higher than the nominal luminosity. The so-called High Luminosity LHC will be in operation for about ten years. Such a long operation means that detectors will be exposed to a very high irradiation dose. These two factors - the high instantaneous luminosity and the large irradiation dose - require more robust and higher granularity detectors and significantly faster data transmission and analysis. To face these challenges the CMS detector will be significantly upgraded in the coming years. It is planned to completely rebuild the tracker system, endcap calorimeters and install a new MIP (minimum ionizing particle) timing detector. In this paper a brief review of the CMS detector upgrades will be given, with more details on the tracker, the calorimeters and the timing detector.

Large-area Si(Li) detectors for X-ray spectrometry and particle tracking in the GAPS experiment

The first lithium-drifted silicon (Si(Li)) detectors to satisfy the unique geometric, performance, and cost requirements of the General Antiparticle Spectrometer (GAPS) experiment have been produced by Shimadzu Corporation. The GAPS Si(Li) detectors will form the first large-area, relatively high-temperature Si(Li) detector system with sensitivity to X-rays to operate at high altitude. These 10 cm-diameter, 2.5 mm-thick, 4- or 8-strip detectors provide the active area, X-ray absorption efficiency, energy resolution, and particle tracking capability necessary for the GAPS exotic-atom particle identification technique. In this paper, the detector performance is validated on the bases of X-ray energy resolution and reconstruction of cosmic minimum ionizing particle (MIP) signals. We use the established noise model for semiconductor detectors to distinguish sources of noise due to the detector from those due to signal processing electronics. We demonstrate that detectors with either 4 strips or 8 strips can provide the required ≲4 keV (FWHM) X-ray energy resolution at flight temperatures of −35 to −45̂C, given the proper choice of signal processing electronics. Approximately 1000 8-strip detectors will be used for the first GAPS Antarctic balloon flight, scheduled for late 2021.

Monte Carlo simulation of charge collection processes in Monolithic Active Pixel Sensors for the ALICE ITS upgrade

Abstract A precise simulation of the response of Monolithic Active Pixel Sensors (MAPS) is difficult to achieve because of the difficulty in describing the charge collection process both in the epitaxial layer, a typically only partially depleted active volume, and in the substrate, a low resistivity bulk, of the sensor. Transient TCAD simulations provide good description of the electric field, but are too slow to be used in the simulation and analysis chain of HEP experiments. Therefore a faster simulation of the sensor response is necessary in order to provide in-depth understanding of the detector response. A fast tool developed to model the response of ALPIDE, the MAPS for the upgrade of the ALICE Inner Tracking System (ITS), is presented in this paper. The basic concept is a first principles Monte Carlo (MC) simulation, using the electric fields extracted from a TCAD simulation to model the drift of the charge carriers. That is, the more complex part of the simulation is handled by TCAD while preserving the speed of the MC simulation with only one free parameter — the external electric field strength. The tool is versatile, any MAPS architecture can be simulated once the proper external electric field is provided, and in this paper it has been done for two chips, developed for the ALICE ITS upgrade, INVESTIGATOR (analogue output) and ALPIDE (digital output). It will be shown that an excellent agreement between data and simulation has been achieved, both for 55Fe X-rays and minimum ionising particles.

Inverse Low Gain Avalanche Detectors (iLGADs) for precise tracking and timing applications

Low Gain Avalanche Detector (LGAD) is the baseline sensing technology of the recently proposed Minimum Ionizing Particle (MIP) end-cap timing detectors (MTD) at the Atlas and CMS experiments. The current MTD sensor is designed as a multi-pad matrix detector delivering a poor position resolution, due to the relatively large pad area, around 1 mm2; and a good timing resolution, around 20–30 ps. Besides, in his current technological incarnation, the timing resolution of the MTD LGAD sensors is severely degraded once the MIP particle hits the inter-pad region since the signal amplification is missing for this region. This limitation is named as the LGAD fill-factor problem. To overcome the fill factor problem and the poor position resolution of the MTD LGAD sensors, a p-in-p LGAD (iLGAD) was introduced. Contrary to the conventional LGAD, the iLGAD has a non-segmented deep p-well (the multiplication layer). Therefore, iLGADs should ideally present a constant gain value over all the sensitive region of the device without gain drops between the signal collecting electrodes; in other words, iLGADs should have a 100% fill-factor by design. In this paper, tracking and timing performance of the first iLGAD prototypes is presented.

Characterization of the Radiation Field in the ATLAS Experiment With Timepix Detectors

We present a study of the radiation field at various locations in the ATLAS experiment, using compact detector systems based on pixelated silicon sensors assembled with Timepix readout chips. The hodoscope design of the ATLAS-Timepix (TPX) detectors includes neutron converters in between two sensors, allowing the characterization of both neutron and charged particle fields on a track by track basis. Thermal and fast neutrons are discriminated by segmenting the sensor area with dedicated sensitive materials. Using specific pattern recognition algorithms, clusters from electrons and photons above ~10 keV, minimum ionizing particles (MIPs), and highly ionizing particles are classified. A coincidence method using the time-over-threshold mode of the chip is developed to extract stopping power and directional information of energetic charged particles. Thermal neutron fluences are obtained for each ATLAS-TPX unit, illustrating the effect of detector material and shielding in the experimental cavern. Reconstructed trajectories of energetic charged particles point out radiation coming from the interaction point and other hot spots.

The Readout Electronics Research Design and Development for CEPC Scintillators Electromagnetic Calorimeter Prototype

The Circular Electron Positron Collider (CEPC) is a proposing electron–positron collider in China, which aims for generating high center-of-mass energy colliding above 250 GeV. The high-granularity electromagnetic calorimeter (ECAL) is included in a calorimeter system, which is mainly responsible for the measurement of photon. A particle flow algorithm (PFA)-based ECAL solution will utilize about 400k channels/m3. Here, we present the design and development status of readout electronics based on SPIROC2b for the CEPC ECAL with high-granularity scintillants and silicon photomultipliers (SiPMs). The readout electronics consists of front-end electronics (FEE), data interface (DIF) board, and data acquisition (DAQ) board. The front-end board (FEB) carries SiPMs (S12571-010P), scintillants (PSD), and FEB application-specific integrated circuit (ASIC) (SPIROC2b). Two electronics were designed in this paper, one is for ASIC functionality and performance only, and the other is used as a single layer of a further prototype of ECAL. Electronic test and cosmic ray test have been done to electronics. The results indicate that a charge dynamic from 62 fC to 300 pC at S/N = 2 is successfully achieved, and the minimum ionizing particles (MIPs) are separated from the pedestal.

Time-delayed electrons from Higgs decays to right-handed neutrinos

We consider the physics reach at the high luminosity LHC (HL-LHC) using the timing capability of a minimum ionizing particle (MIP) timing layer and the electromagnetic calorimeter in the CMS experiment for a simplified right-handed neutrino effective theory. In the simplified model, the lightest right-handed neutrinos are produced through Higgs decay with mean decay lengths of order mathcal{O} (0.1 m − 100 m) and then subsequently decay into final states that include electrons. We consider the effect of several different kinematic cuts for a timing based analysis of this model. We demonstrate that if timing information can be successfully incorporated into the event trigger, it is possible to probe the Higgs branching ratio to two right-handed neutrinos to the order mathcal{O} (10−5) for a range of different right-handed neutrino lifetimes.

Ion charge separation with new generation of nuclear emulsion films

Abstract In hadron therapy, the accelerated ions, interacting with the body of the patient, cause the fragmentation of both projectile and target nuclei. The fragments interact with the human tissues depositing energy both in the entrance channel and in the volume surrounding the tumor. The knowledge of the fragments features is crucial to determine the energy amount deposited in the human body, and - hence - the damage to the organs and to the tissues around the tumor target. The FOOT (FragmentatiOn Of Target) experiment aims at studying the fragmentation induced by the interaction of a proton beam (150-250 MeV/n) inside the human body. The FOOT detector includes an electronic setup for the identification of Z ≥ 3 fragments integrated with an emulsion spectrometer to measure Z ≤ 3 fragments. Charge identification by nuclear emulsions is based on the development of techniques of controlled fading of the particle tracks inside the nuclear emulsion, that extend the dynamical range of the films developed for the tracking of minimum ionising particles. The controlled fading strongly depends on temperature, relative humidity and treatment duration. In this study the performances in terms of charge separation of proton, helium and carbon particles, obtained on a batch of new emulsion films produced in Japan are reported.

Properties of HPK UFSD after neutron irradiation up to 6e15 n/cm2

In this paper we report results from a neutron irradiation campaign of Ultra-Fast Silicon Detectors (UFSD) with fluences of 1e14, 3e14, 6e14, 1e15, 3e15, 6e15 n/cm2. The UFSD used in this study are circular 50 micro-meter thick Low-Gain Avalanche Detectors (LGAD), with a 1.0 mm diameter active area. They have been produced by Hamamatsu Photonics (HPK), Japan, with pre-radiation internal gain in the range 10-100 depending on the bias voltage. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particle (MIPs) from a 90Sr based \b{eta}-source. The leakage current, internal gain and the timing resolution were measured as a function of bias voltage at -20C and -30C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction method for both. The dependence of the gain upon the irradiation fluence is consistent with the concept of acceptor removal and the gain decreases from about 80 pre-irradiation to 7 after a fluence of 6e15 n/cm2. Consequently, the timing resolution was found to deteriorate from 20 ps to 50 ps. The results indicate that the most accurate time resolution is obtained at a value of the constant fraction discriminator (CFD) threshold used to determine the time of arrival varying with fluence, from 10% pre-radiation to 60% at the highest fluence. Key changes to the pulse shape induced by irradiation, i.e. (i) a reduce sensitivity of the pulse shape on the initial non-uniform charge deposition, (ii) the shortening of the rise time and (iii) the reduced pulse height, were compared with the WF2 simulation program and found to be in agreement.

Time resolution studies of Timepix3 assemblies with thin silicon pixel sensors

Timepix3 is a multi-purpose readout ASIC for hybrid pixel detectors. It can measure time and amplitude simultaneously by employing time-of-arrival (ToA) and time-over-threshold (ToT) techniques. Both methods are systematically affected by timewalk. In this paper, a method for pixel-by-pixel calibration of the time response is presented. Assemblies of Timepix3 ASICs bump-bonded to thin planar silicon pixel sensors with thicknesses of 50 μ m, 100 μ m and 150 μ m are calibrated and characterised in particle beams. For minimum ionising particles, time resolutions down to 0.72 ± 0.04 ns are achieved.

Beam-tests of prototype modules for the CMS High Granularity Calorimeter at CERN

As part of its HL-LHC upgrade program, CMS is developing a High Granularity Calorimeter (HGCAL) to replace the existing endcap calorimeters. The HGCAL will be realised as a sampling calorimeter, including 36 layers of silicon pads and 16 layers combining both silicon+scintillator detectors interspersed with metal absorber plates. Starting from 2016, prototype modules, based on 6-inch hexagonal silicon pad sensors with pad areas of 1.0 cm2, have been constructed. In 2017 and 2018, beam tests of different sampling configurations made from these modules have been conducted at CERN's SPS using beams of charged hadrons and electrons with momenta from 20 to 350 GeV/c. The setup was complemented with CALICE's AHCAL prototype, a scintillator-based sampling calorimeter, mimicking the proposed design of the HGCAL's scintillator part. Most importantly, the new Skiroc2-CMS readout ASIC has been used in the silicon modules, facilitating the study of its timing capabilities in practice. This talk summarises the test beam efforts in 2017 and 2018. Preliminary results, including gain characterisation, calibration with minimum ionising particles and energy reconstruction performance of electron induced showers are shown.

Calibration of the DAMPE Plastic Scintillator Detector and its on-orbit performance

The DArk Matter Particle Explorer (DAMPE) is a space-borne apparatus for detecting the high-energy cosmic-ray-like electrons, γ-rays, protons and heavy ions. The Plastic Scintillator Detector (PSD) is the top-most sub-detector of the DAMPE. The PSD is designed to measure the charge of incident high-energy particles and it also serves as a veto detector for discriminating γ-rays from charged particles. In this paper, a PSD on-orbit calibration procedure is described, which includes the five steps of pedestal, dynode correlation, response to minimum-ionizing particles, light attenuation function and energy reconstruction. A method for reconstructing the charge of incident high energy cosmic-ray particles is introduced. The detection efficiency of each PSD strip is verified to be above 99.5%; the total efficiency of the PSD for charged particles is above 99.99%.

Simulations of electrical properties of cylindrical 3d-trench electrical si detectors under different radiation fluences and mip incident position

In this work, we investigate the dependence of charge collection on the MIP(minimum ionizing particle) incident position for cylindrical 3D-Trench electrode Si detectors being irradiated to various fluences. Simulation results are: (1) For non-irradiated detectors, detector charge collection does not depend on the MIP incident position, i.e. the charge collection is always a constant, there is no effect of trapping; (2) For irradiated detectors, detector charge collection depends on the MIP incident position; (3) As radiation fluence increases, detector charge collection decreases, regardless of MIP incident position. This is due to the fact that charge trapping by radiation induced defects also increases with radiation fluences, resulting in less charge collection.

DesigningOptimalBiasVoltageforRadiotherapy Diamond Dosimeter

Introduction: Recent developments of radiotherapy techniques, require high accuracy detectors to determine the delivered dose in a small area. Chemical vapor deposition (CVD) or naturally growth diamond detectors which are commercially available are good candidates for this purpose. In these detectors two electrodes with high different electrical potential are deposited on both sides of a diamond, and the incident radiation generates a current which indicates absorbed dose. However, the large band gap makes diamond an excellent electrical insulator, but care must be taken to eliminate the air ionization contribution to the photocurrent. For this reason, the device must operate in vacuum. In the other hand, patient’s safety needs a decrease in detector’s voltage. In this simulation study, it is indicated that the applied voltage can be decreased to about 50[V] without loss of dosimeter’s sensitivity. Materials and methods: In this work Weightfield2 software, which is a program to simulate current signals in a silicon or diamond detector was used. This program uses GEANT4 libraries to simulate the energy released by an interacting particle. Minimum Ionizing Particle (MIP) with a 250 micrometers thick pure diamond was used and then the bias voltage was increased from 1 [V] to 500 [V], then the curve of time response and current response of the sensor was observed as a function of bias voltage. Results: The results indicate that the applied voltage can reduce up to about 50 [V] with a reasonable 40 [ns] time response. This can be achieved by the benefit of high accuracy and fast Analog to Digital Converters (ADCs). Conclusion: With new generation of synthetic diamonds known as single crystal CVDs, which their characteristic is very similar to natural diamond, and with modern electric measuring devices, in contrast to the current sensors, it is possible to reduce the applied voltage of dosimeter electrodes to about 50 [V].

First beam tests of prototype silicon modules for the CMS High Granularity Endcap Calorimeter

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. We present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation.

Comparison of 35 and [formula omitted]m thin HPK UFSD after neutron irradiation up to 6 [formula omitted] 1015 neq/cm2

We report results from the testing of 35 μm thick Ultra-Fast Silicon Detectors (UFSD) produced by Hamamatsu Photonics (HPK), Japan and the comparison of these new results to data reported in a previous paper on 50 μm thick UFSD produced by HPK. The 35 μm thick sensors were irradiated with neutrons to fluences of 1 ⋅ 1014, 1 ⋅ 1015, 3 ⋅ 1015, 6 ⋅ 1015 neq/cm2. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particles (MIPs) from a 90Sr β-source. The leakage current, capacitance, internal gain and the timing resolution were measured as a function of bias voltage at −20 °C and −27 °C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction discrimination method for both devices. Within the fluence range measured, 35 μm thick UFSD present advantages in timing accuracy, bias voltage and power consumption.

Readout Electronics for CEPC Semidigital Hadron Calorimeter Preprototype

Circular Electron and Positron Collider (CEPC) is a large experiment facility proposed by the Chinese particle physics community. One of the running options is being the Higgs factory. The calorimeter is the main part of this experiment to measure the jet energy. Semidigital hadron calorimeter (SDHCAL) is one of the options for the hadron measurement. Gas electron multiplier (GEM) detector with its high-position resolution and flexible configuration is one of the candidates for the active layer of the SDHCAL. The main purpose of this paper is to provide a feasible readout method for the GEM-based SDHCAL. A smallscale prototype is designed and implemented, including front-end board (FEB) and data interface board (DIF). The prototype electronics has been tested. The equivalent rms noise of all channels is below 0.35 fC. The dynamic range is up to 500 fC and the gain variation is less than 1%. The readout electronics is applied on a double-layer GEM detector with 1 cm × 1 cm readout pad. The result indicates that the electronics works well with the detector. The detection efficiency of minimum ionization particle (MIP) is over 95% with a 5-fC threshold.

A SKIROC2-based prototype electronics system for silicon PIN array

Silicon PIN (Si-PIN) diode has been widely used in high-energy physics experiments. The next-generation experiments ask for a large amount of the Si-PIN diode arrays, leading to a requirement for the electronics system with features of higher integration and lower power consumption than the traditional ones. The aim was to design and implement a prototype of multi-channel electronic system, which is based on the SKIROC2 ASIC. The system is also considered as the pre-research of the silicon–tungsten (Si-W) ECAL for CEPC. The prototype is divided into two parts, so that it has the potentiality for the expansion of more readout channels. The front-end board (FEB), which carries a Si-PIN diode array and an ASIC of SKIROC2 on it, provides high voltage to the Si-PIN diodes and processes the signals as well. The FEB is configured by a data interface board (DIF) and sends data to the DIF, which then transfers data to PC via USB interface after packing process. The prototype electronics system has been implemented. The equivalent noise level of all the 64 channels is below 0.4 fC. The dynamic range is up to +3000 fC with an integral nonlinearity (INL) of 0.2 %, and the gain non-uniformity is better than 5 %. The energy resolution with 59 keV X-rays from 241Am is about 13.3 % (in RMS), while the signal-to-noise ratio (SNR) reaches about 10.9 for minimum ionizing particles (MIPs). In this paper, a SKIROC2-based prototype electronics system for Si-PIN array, as well as the performance test, has been presented. The system has features of high integration, low noise, and high dynamic range. The SKIROC2, as well as the design concept of the electronics system, can be applied to the preliminary prototype Si-W ECAL of CEPC.

Studies of detector cells for a hadronic calorimeter based on plastic scintillators

In this paper, we study variations of a plastic scintillator tile coupled to silicon photomultiplier via a dome-shaped cavity originally developed in the CALICE collaboration. Four kinds of plastic scintillator detector cells with different sizes based on the structure were studied for applications in analog readout highly granular hadronic calorimeter (AHCAL) in future circular electron positron collider (CEPC) project. The responses to cosmic rays of the detector cells could reach 33.89 p.e./MIPs (minimum ionizing particles). The good results of both response uniformity and MIP detection efficiency (above 95%) show that the detector cells with larger sizes ( $$40\times 40\times 3$$ and $$50\times 50\times 3\,\hbox {mm}^{3}$$ ) could provide an option for AHCAL detector cells of CEPC detectors.

TCAD simulation of a single Monolithic Active Pixel Sensors based on High Voltage CMOS technology

ABSTRACTA model of a High Voltage CMOS (HV-CMOS) Monolithic Active Pixel Sensor (MAPS) has been modelled using Technology Computer Aided Design (TCAD). The model has incorporated both the active region and the on-pixel readout circuits which were comprised of a source follower amplifier and an integrated charge amplifier. The simulation has examined the electrical characteristics and response output of a HV-CMOS MAPS sensor using typical dimensions, levels of doping in the structural layers and bias conditions for this sensor. The performance of two alternate designs of amplifier have been examined as a function of the operating parameters. The response of the sensor to the incidence of Minimum Ionizing Particles (MIPs) at different energies has been included in the model.