Resolution Electron Energy Research Articles

The ATLAS experiment at the CERN Large Hadron Collider: a description of the detector configuration for Run 3

The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of ℒ = 2 × 1034 cm-2 s-1 was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of ℒ = 2 × 1034 cm-2 s-1, with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector.

Optical properties of InSb derived from reflection electron energy loss spectroscopy spectrum

The energy loss function (ELF) of the narrow bandgap semiconductor, InSb, was derived from the reflection electron energy loss spectroscopy (REELS) spectrum measured at 4 keV incident electron energy in an energy loss range of 1.6–200 eV using a high energy resolution electron spectrometer. The experimental spectrum was analyzed with the reverse Monte Carlo (RMC) method, which integrates the classical trajectory Monte Carlo simulation with the simulated annealing method for optimizing the trial ELF. Subsequently, the complex dielectric function ε(ω), refractive index and extinction coefficient were determined from the obtained ELF in the energy loss (i.e. photon energy) range of 1.6–200 eV. The validity of the obtained data was verified by the f-sum rule, ps-sum rule, inertial sum rule and dc-conductivity sum rule. We found that our calculated data of InSb fulfill the sum rules with very high accuracy; therefore, the use of these calculated optical data in material science and surface analysis is highly recommended for further applications.

Momentum resolved band gap measurement by high energy resolution electron energy loss spectroscopy

Momentum resolved band gap measurement by high energy resolution electron energy loss spectroscopy

Dissociative electron attachment studies of gas-phase acetic acid using a velocity map imaging technique

Advancing instrumentation to explore dissociative electron attachment (DEA) studies allows previously unattainable information to be acquired. Using a newly constructed velocity map imaging spectrometer, we revisited a study on DEA to gas-phase acetic acid. We discuss possible fragmentation channels and compared the corresponding ion yields with previous high electron-energy resolution results. We focus on the channels occurring at higher energies, particularly near 10 eV, and calculate their thermodynamic thresholds. Moreover, we expand previous studies and perform time-sliced imaging near the 10 eV resonance to obtain the kinetic energy distribution of the fragment ions.

Performance evaluation of a single microchannel plate with large length-to-diameter ratio

The conventional microchannel plate (MCP) detector has found widespread application in various fields. This article focuses on investigating the performance of a single MCP with a large length-to-diameter ratio (L/D) of 80:1, particularly for single electron counting. To enhance MCP performance, alumina with a high secondary electron yield (SEY) is coated onto the MCP using atomic layer deposition (ALD). The SEYs of alumina thin films with different thicknesses are measured using a pulsing electron beam method. The 80:1 L/D MCPs operate in electron counting mode, and the optimal alumina thickness is determined through a comparative study of MCP performance before and after coating. The relationships between maximum SEY, primary electron energy, gain, peak-to-valley ratio (P/V), and pulse height resolution (PHR) are analyzed. After alumina coating, the single 80:1 MCP exhibits improved gain, P/V and PHR. The optimal P/V and PHR of a single MCP as functions of the primary electron energy align with the relationship between the SEY of the alumina coating and the primary electron energy. Additionally, the variation of DC gain with extracted charge is investigated. This article provides valuable insights for parameter selection in achieving the optimal working state of MCP and explores the potential application of single electron counting using a single MCP.

Automatic and Quantitative Measurement of Spectrometer Aberrations.

The performance of electron energy loss spectrometers can often be limited by their electron optical aberrations. Due to recent developments in high energy resolution and momentum-resolved electron energy loss spectroscopy (EELS), there is renewed interest in optimizing the performance of such spectrometers. For example, the "ω - q" mode of momentum-resolved EELS, which uses a small convergence angle and requires aligning diffraction spots with the slot aperture, presents a challenge in the realignments of the spectrometer required by the adjustment of the projection lenses. Automated and robust alignment can greatly benefit such a process. The first step toward this goal is automatic and quantitative measurement of spectrometer aberrations. We demonstrate the measurement of geometric aberrations and distortions in EELS within a monochromated scanning transmission electron microscope (STEM). To better understand the results, we present a wave mechanical simulation of the experiment. Using the measured aberration and distortion coefficients as inputs to the simulation, we find a good match between the simulation and experiment, verifying formulae used in the simulation. From verified simulations with known aberration coefficients, we can assess the accuracy of measurements. Understanding the errors and inaccuracies in the procedure can guide further progress in aberration measurement and correction for new spectrometer developments.

Optimization of WLS fiber readout for the HERD calorimeter

A novel 3-D calorimeter, composed of about 7500 LYSO cubes, is the key and crucial detector of the High Energy cosmic-Radiation Detection (HERD) facility to be installed onboard the China Space Station. Energy deposition from cosmic ray in each LYSO cube is translated by multiple wavelength shifting (WLS) fibers for multi-range data acquisition and real-time triggering.In this study, various methods of surface finish and encapsulation of the LYSO cube were investigated to optimize the amplitude from the WLS fiber end with the aim of improving the signal-to-noise ratio of Intensified scientific CMOS (IsCMOS) collection. The LYSO cube with five rough surfaces and a specular reflector achieves the maximum amplitude at the low-range fiber end, which is increased by roughly 44% compared to the polished cube with PTFE wrapping.The non-uniformity of amplitude at different positions on the LYSO cube surface was measured by X-ray and the positional correlation factor was derived for the entire cube. A simulation based on HERD CALO was conducted, which revealed that both the LYSO cube with five rough surfaces and the cube with rough bottom face exhibit superior energy resolution for electrons compared to the other two configurations.

Deep learning techniques for energy clustering in the CMS ECAL

The reconstruction of electrons and photons in CMS depends on topological clustering of the energy deposited by an incident particle in different crystals of the electromagnetic calorimeter (ECAL). These clusters are formed by aggregating neighbouring crystals according to the expected topology of an electromagnetic shower in the ECAL. The presence of upstream material (beampipe, tracker and support structures) causes electrons and photons to start showering before reaching the calorimeter. This effect, combined with the 3.8T CMS magnetic field, leads to energy being spread in several clusters around the primary one. It is essential to recover the energy contained in these satellite clusters in order to achieve the best possible energy resolution for physics analyses. Historically satellite clusters have been associated to the primary cluster using a purely topological algorithm which does not attempt to remove spurious energy deposits from additional pileup interactions (PU). The performance of this algorithm is expected to degrade during LHC Run 3 (2022+) because of the larger average PU levels and the increasing levels of noise due to the ageing of the ECAL detector. New methods are being investigated that exploit state-of-the-art deep learning architectures like Graph Neural Networks (GNN) and self-attention algorithms. These more sophisticated models improve the energy collection and are more resilient to PU and noise, helping to preserve the electron and photon energy resolution achieved during LHC Runs 1 and 2. This work will cover the challenges of training the models as well the opportunity that this new approach offers to unify the ECAL energy measurement with the particle identification steps used in the global CMS photon and electron reconstruction.

Enhancing higher-energy spectral resolution for electron particle simulations in air

In the presence of an electric field, electrons would theoretically accelerate asymptotically to relativistic energies. However, regular collisions with air molecules limit the increase in electron energy. The stochastic nature of collisions leaves a theoretical probability that an electron elude inelastic collisions thereby accumulating an atypically high energy. Such an electron, under specific criteria, could be called a “thermal” or “cold runaway”. Depending on the electric field, the runaway probability might be too low to be computationally observed without resorting to Monte Carlo importance sampling. This article provides a method for fixing the spectral energy resolution of electrons through the combined methodology of Russian roulette and probabilistic splitting in order to render the study of runaway mechanism amenable to electron swarm simulations in various plasma physics applications. Program summaryProgram title: particle-energy-compaction.pyCPC Library link to program files:https://doi.org/10.17632/k2y2r73t69.1Developer's repository link:https://osf.io/c6wyhLicensing provisions: CC By 4.0Programming language: Python 3Nature of problem: Currently, electron thermal runaway simulations in electric discharges cannot properly resolve the electron energy-spectrum tail. Most codes apply a super-particle restriction algorithm without efficiently or systematically allocating more space for scarcer electrons located at higher-energies. This results in a poor estimation of the thermal runaway rates at electric fields below the critical runaway threshold.Solution method: We provide a methodology based on the Monte-Carlo variance reduction techniques of Russian roulette and splitting, to allocate particles in different energy domains according to a given target super-particle energy density function. The algorithm converts an input set of super-particle energies and weights into another set that matches the desired spectral resolution. To avoid a sudden surge of super-particles in a low-populated spectral region, the algorithm takes also as input a minimum super-particle weight threshold relative to the physical number of particles in the simulation.Additional comments including restrictions and unusual features: A good knowledge of the problem is required in order to design the target spectrum function. An inappropriate selection of the target spectrum can result in a decrease of spectral resolution or also a severe deterioration of the swarm properties due to large stochastic fluctuations. It is recommended that the users first devise the target spectrum based on the physical spectrum obtained from their simulations, and start designing from there.

The bipolar charge plasma spectrometer (BCPS) based on the 2π-field-of-view double-channel electrostatic analyzer.

In this paper, we propose a bipolar charge plasma spectrometer based on the double-channel electrostatic analyzer for simultaneously measuring thermal ions and electrons with a 2π hemispherical field-of-view. Both ions and electrons within the wide field-of-view enter the spectrometer, pass through the variable geometric factor channel, and are then separated by the double-channel electric fields. Two microchannel plates are accommodated at the exit of the analyzer for ion and electron detection. The main performance of the spectrometer has been obtained from on-ground calibration. With the electrostatic deflectors and the cylindrically symmetric structure, the spectrometer provides simultaneous measurements of thermal ion and electron velocity distributions with a shared field-of-view of 360° (azimuth angle) by 90° (elevation angle) and a broad energy range for both ions and electrons. The ion analyzer constant and the electron analyzer constant are 11.1 and 9.7, respectively. The detecting energy range of 33.3-44.4 keV for ions and 29.1-38.8 keV for electrons can be obtained by using the sweeping electrostatic analyzer voltage range of 3-4000 V. The ion and electron energy resolutions are 9.6% and 6.1%, respectively. The variable geometric factor function provides a large geometric factor adjusting range for both ion and electron measurements by two orders of magnitude, which fulfills the requirements of a large dynamic flux range for simultaneous measurements of space thermal plasma in the solar wind and magnetosphere.

Exploring the intrinsic energy resolution of liquid scintillator to approximately 1 MeV electrons

We propose a novel method for exploring the intrinsic energy resolution of a liquid scintillator (LAB + 2.5 g/L PPO + 3 mg/L bis-MSB) to approximately 1 MeV electrons. With the help of coincidence detection technology, single-energy electrons of 207Bi were effectively selected. With a careful measurement and analysis of the energy resolution of a small liquid scintillator detector, the intrinsic energy resolution of the liquid scintillator to 976 keV electrons was extracted to be 1.83% ± 0.06%. We used the wide-angle Compton coincidence (WACC) method to measure the luminescent nonlinearity of a liquid scintillator and found that it contributes only weakly to the intrinsic energy resolution of electrons. Such an unexpected large intrinsic energy resolution may come from fluctuations in energy transfer processes.

Energy resolution of Compton electrons in LaCl3:Ce using compact digitizer

Energy resolution of Compton electrons in LaCl3:Ce using compact digitizer

Electron and photon responses of CWO scintillation crystal

The electron response and photon response of cadmium tungstate crystal (CWO) scintillation crystal have been investigated. For the photon response measurement, the 133Ba, 22Na, 137Cs and 60Co were used as radioactive sources in the energy range of 356–1332 keV. For the electron response measurement, the 137Cs source with gamma energy at 662 keV was used for the measurement of the coincidence electron energy spectra at seven scattering angles from 30° to 120°. The seven consistent electron energies were found in the range of 101.27–443.27 keV. The light yield results for both techniques showed a slight increase when gamma energy increased. Besides, for the energy resolutions and electron energy resolutions, the graph showed the relationship between the electron energy resolution and the inverse of the square root of the electron energy.

Quaternary Semiconductor Cd1−xZnxTe1−ySey for High-Resolution, Room-Temperature Gamma-Ray Detection

The application of Cd0.9Zn0.1Te (CZT) single crystals, the primary choice for high-resolution, room-temperature compact gamma-ray detectors in the field of medical imaging and homeland security for the past three decades, is limited by the high cost of production and maintenance due to low detector grade crystal growth yield. The recent advent of its quaternary successor, Cd0.9Zn0.1Te1−ySey (CZTS), has exhibited remarkable crystal growth yield above 90% compared to that of ~33% for CZT. The inclusion of Se in appropriate stoichiometry in the CZT matrix is responsible for reducing the concentration of sub-grain boundary (SGB) networks which greatly enhances the compositional homogeneity and growth yield. SGB networks also host defect centers responsible for charge trapping, hence their reduced concentration ensures minimized charge trapping. Indeed, CZTS single crystals have shown remarkable improvement in electron charge transport properties and energy resolution over CZT detectors. However, our studies have found that the overall charge transport in CZTS is still limited by the hole trapping. In this article, we systematically review the advances in the CZTS growth techniques, its performance as room-temperature radiation detector, and the role of defects and their passivation studies needed to improve the performance of CZTS detectors further.

The Advantage of Nanowire Configuration in Band Structure Determination

AbstractEarth‐abundant and environmentally friendly semiconductors offer a promising path toward low‐cost mass production of solar cells. A critical aspect in exploring new semiconducting materials and demonstrating their enhanced functionality consists in disentangling them from the artifacts of defects. Nanowires are diameter‐tailored filamentary structures that tend to be defect‐free and thus ideal model systems for a given material. Here, an additional advantage is demostrated, which is the determination of the band structure, by performing high energy and spatial resolution electron energy‐loss spectroscopy in aloof and inner beam geometry in a scanning transmission electron microscope. The experimental results are complemented by spectroscopic ellipsometry and are excellently correlated with first principles calculations. This study opens the path for characterizing the band structure of new compounds in a non‐destructive and prompt manner, strengthening the route of new materials discovery.

Arbitrary EEDF determination of atmospheric-pressure plasma by applying machine learning to OES measurement

A new method to determine the arbitrary electron energy distribution function (EEDF) from the optical emission spectroscopic measurement in atmospheric-pressure plasma is introduced. The optical emission spectroscopy (OES) continuum emission spectrum, dominated by electron-neutral bremsstrahlung radiation, is analyzed to inspect the usefulness of the conventional OES measurement range for EEDF determination. The EEDF is reconstructed from the OES continuum radiation spectrum by applying machine learning to solve the bremsstrahlung emissivity equation inversely. Through iterative statistical analysis, the presented genetic algorithm can locate the EEDF reliably. Verification of the algorithm shows that theoretical Maxwellian and Druyvesteynian EEDFs can be partially reconstructed from a realistic OES measurement range. Furthermore, preliminary experimental EEDF results of an argon dielectric barrier discharge (DBD) OES measurement are given. The electron energy range and resolution of the determined EEDF are discussed. The results in this paper show potential for accurate determination of the arbitrary EEDF in atmospheric-pressure plasma using simple OES equipment.

High spatial and energy resolution electron energy loss spectroscopy of the magnetic and electric excitations in plasmonic nanorod oligomers.

We leverage the high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron microscopy to study the hybridization of cyclic assemblies of plasmonic gold nanorods. Detailed experiments and simulations elucidate the hybridization of the coupled long-axis dipole modes into collective magnetic and electric dipole plasmon resonances. We resolve the magnetic dipole mode in these closed loop oligomers with electron energy loss spectroscopy and confirm the mode assignment with its characteristic spectrum image. The energy splitting of the magnetic mode and antibonding modes increases with the number of polygon edges (n). For the n=3-6 oligomers studied, optical simulations using normal incidence and s-polarized oblique incidence show the respective electric and magnetic modes' extinction efficiencies are maximized in the n=4 arrangement.

Optimizing the performance of the CMS Electromagnetic Calorimeter to measure Higgs properties during Phase I and Phase II of the LHC

The CMS Electromagnetic Calorimeter (ECAL), is a high granularity lead tungstate (PbWO4) crystal calorimeter operating at the CERN LHC. The ECAL performance has been crucial in the discovery and subsequent characterization of the Higgs boson. The original ECAL design considerations, and the improvements to the energy reconstruction and energy calibration algorithms to cope with the LHC Run II are described. For the High-Luminosity LHC (HL-LHC) upgrades to ECAL are necessary. The crystals in the barrel region will be retained, defining the HL-LHC CMS barrel electromagnetic calorimeter ECAL. The readout electronics will be upgraded and operating at lower temperatures, to maintain the required performance of ECAL from 2027 onwards. The new readout electronics, the timing resolution and the electron and photon reconstruction efficiencies and energy resolution expected for HL-LHC are presented. The performance relevant to a number of key Higgs decay channels is reported.

The ENUBET positron tagger prototype: construction and testbeam performance

A prototype for the instrumented decay tunnel of ENUBET was tested in 2018 at the CERN East Area facility with charged particles up to 5 GeV . This detector is a longitudinal sampling calorimeter with lateral scintillation light readout. The calorimeter was equipped by an additional “t0-layer” for timing and photon discrimination. The performance of this detector in terms of electron energy resolution, linearity, response to muons and hadron showers are presented in this paper and compared with simulation. The t0-layer was studied both in standalone mode using pion charge exchange and in combined mode with the calorimeter to assess the light yield and the 1 mip/2 mip separation capability. We demonstrate that this system fulfills the requirements for neutrino physics applications and discuss performance and additional improvements.

Performance of CMS High Granularity Calorimeter prototypes in beam test experiments

The present electromagnetic and hadronic calorimeters of the CMS experiment will be upgraded to cope with the harsh radiation environment and pileup conditions posed by the high luminosity operations of the LHC (HL-LHC) expected to start in 2027. The CMS collaboration has opted for a sampling calorimeter in the endcap sections of the detector, based on silicon and scintillator technologies, with unprecedented transverse and longitudinal segmentation to facilitate particle identification, particle-flow reconstruction and pileup rejection. As part of the ongoing development and testing phase of this High Granularity Calorimeter (HGCAL), prototypes of both the silicon and scintillator based calorimeter sections have been tested in 2018 in beams at CERN. We report on the performance of the prototype detectors in terms of stability of noise and pedestals, calibration with minimum-ionizing-particles (MIPs), and energy linearity and resolution for electrons and pions. We compare the measurements with a detailed GEANT4-based simulation.