Electromagnetic Calorimetry Research Articles

Study of time resolution measurements and prospects for energy resolution of an ultra-compact sampling calorimeter (RADiCAL) module at EM shower maximum over the energy range 25 GeV 150 GeV

The RADiCAL Collaboration is conducting R&D on high performance electromagnetic (EM) calorimetry to address the challenges expected in future collider experiments under conditions of high luminosity and/or high irradiation (FCC-ee, FCC-hh, fixed target and forward physics environments). Under development is a sampling calorimeter approach, known as RADiCAL modules, based on scintillation, wavelength-shifting (WLS) technologies and photosensor, including SiPM or SiPM-like technology. The modules discussed herein consist of alternating layers of very dense tungsten (W) absorber and scintillating crystal Lutetium Yttrium Orthosilicate LYSO(Ce) plates, assembled to a depth of 25 X0. The scintillation signals produced by the EM showers in the region of EM shower maximum (shower max) are transmitted to SiPM located at the upstream/downstream ends of the modules via quartz capillaries which penetrate the full length of the module. The capillaries contain DSB1 organic plastic WLS filaments positioned within the region of shower max, where the shower energy deposition is greatest, then fused with quartz rod elsewhere. The wavelength shifted light from this spatially-localized shower max region is then propagated to the photosensors. This paper presents the results of an initial measurement of the time resolution of a RADiCAL module over the energy range 25 GeV ≤ E ≤ 150 GeV using the H2 electron beam at CERN. The data indicate an energy dependence of the time resolution that follows the functional form: σt=a/E⊕b, where a = 256 GeV ps and b = 17.5 ps. The time resolution measured at the highest electron beam energy for which data was currently recorded (150 GeV) was found to be σt = 27 ps.

Current and future challenges when operating the ATLAS Liquid Argon Calorimeter

The Liquid Argon (LAr) Calorimeters are employed by ATLAS for precision electromagnetic calorimetry and for hadronic and forward calorimetry. They also provide inputs to the first level of the ATLAS trigger system.The LAr Calorimeters have been operated during regular ATLAS data taking since 2008. All critical parameters, like LAr purity and temperature, have been kept at stable values resulting in reliable signal pulses. In 2022, the LHC collider has increased the luminosity leading to a pile-up of up to 70 interactions per bunch crossing. In the high luminosity phase, HL-LHC, planned to be fully functional in 2029, the pile-up will increase up to 200 interactions per bunch crossing.This contribution will highlight the present and future challenges in the operation of such a detector.

Energy calibration through X-ray absorption of the DECAL sensor, a monolithic active pixel sensor prototype for digital electromagnetic calorimetry and tracking

In calorimetry, the predominant detection principle is to measure the energy deposited by particles within a shower initiated by an incident particle. An alternative concept is a sampling calorimeter where the highly granular active layers rather measure the number of secondary particles in the shower by detecting hits through binary readout similar to sensors for tracking applications. In this context, the DECAL sensor is a fully-depleted monolithic active pixel sensor prototype with reconfigurable readout for digital electromagnetic calorimetry and tracking. Its 64 × 64 pixels with a pitch of 55 µm are fabricated in a modified TowerJazz 180 nm CMOS imaging process using a 25 µm epitaxial silicon layer. The readout at 40 MHz is configurable in counting hits in the sensor grouped as either 64 strips or 4 pads. In this article, we present the energy calibration of this sensor using a gamma source of americium-241 as well as X-ray fluorescence at various wavelengths. The uniformity of the pixel responses is shown, allowing the summation of counts across all pixels. By that, two standalone energy calibration methods are developed that describe the X-ray absorption in the energy range of 4–60 keV and agree with each other. The signal pulse height is related to the absorbed photon energy with a 5.54 ± 0.37 mV/keV scale which corresponds to a conversion gain of cg = 19.95 ± 1.32 μV/e−. The relative energy resolution for photon absorption is found to be σE/E = 11.8 ± 3.0%. The absolute counts observed with the DECAL sensor agree with expectations and substantiate the assumption of a fully depleted epitaxial layer. The understanding of the photon absorption is an important input for further development of the sensor towards a multi-layer calorimeter.

A high-performance custom photodetection system to probe the light yield enhancement in oriented crystals

Scintillating homogeneous detectors represent the state of the art in electromagnetic calorimetry. Moreover, the currently neglected crystalline nature of the most common inorganic scintillators can be exploited to achieve an outstanding performance boost in terms of compactness and energy resolution. In fact, it was recently demonstrated by the AXIAL/ELIOT experiments that a strong reduction in the radiation length inside PWO, and a subsequent enhancement in the scintillation light emitted per unit thickness, are attained when the incident particle trajectory is aligned with a crystal axis within ~ 1°. A SiPM-based system has been developed to directly probe this remarkable effect by measuring the scintillation light emitted by a PWO sample. The same concept could be applied to full-scale detectors that would feature a design significantly more compact than currently achievable and unparalleled resolution in the range of interest for present and future experiments.

Secondary Emission Calorimetry

Electromagnetic calorimetry in high-radiation environments, e.g., forward regions of lepton and hadron collider detectors, is quite challenging. Although total absorption crystal calorimeters have superior performance as electromagnetic calorimeters, the availability and the cost of the radiation-hard crystals are the limiting factors as radiation-tolerant implementations. Sampling calorimeters utilizing silicon sensors as the active media are also favorable in terms of performance but are challenged by high-radiation environments. In order to provide a solution for such implementations, we developed a radiation-hard, fast and cost-effective technique, secondary emission calorimetry, and tested prototype secondary emission sensors in test beams. In a secondary emission detector module, secondary emission electrons are generated from a cathode when charged hadron or electromagnetic shower particles penetrate the secondary emission sampling module placed between absorber materials. The generated secondary emission electrons are then multiplied in a similar way as the photoelectrons in photomultiplier tubes. Here, we report on the principles of secondary emission calorimetry and the results from the beam tests performed at Fermilab Test Beam Facility as well as the Monte Carlo simulations of projected, large-scale secondary emission electromagnetic calorimeters.

ATLAS LAr Calorimeter Commissioning for the LHC Run 3

The Liquid Argon Calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region |η|<3.2, and for hadronic and forward calorimetry in the region from |η|=1.5 to |η|=4.9. They also provide inputs to the first level of the ATLAS trigger. After a successful period of data taking during the LHC Run 2 between 2015 and 2018, the ATLAS detector entered into a long period of shutdown. In 2022, the LHC will restart and the Run 3 period should see an increase of luminosity and pile-up of up to 80 interactions per bunch crossing. To cope with these harsher conditions, a new trigger readout path has been installed during the long shutdown. This new path should significantly improve the triggering performance on electromagnetic objects. This will be achieved by increasing the granularity of the objects available at trigger level by up to a factor of ten. The installation of this new trigger readout chain also required the update of the legacy system. More than 1500 boards of the precision readout have been extracted from the ATLAS pit, refurbished and re-installed. The legacy analog trigger readout, which will remain during the LHC Run 3 as a backup of the new digital trigger system, has also been updated. For the new system, 124 new on-detector boards have been added. Those boards that are operating in a radiative environment are digitizing the calorimeter trigger signals at 40 MHz. The digital signal is sent to the off-detector system and processed online to provide the measured energy value for each unit of readout. In total up to 31 Tbps are analyzed by the processing system and more than 62Tbps are generated for downstream reconstruction. To minimize the triggering latency the processing system had to be installed underground. The limited available space imposed a very compact hardware structure. To achieve a compact system, large FPGAs with high throughput have been mounted on ATCA mezzanines cards. In total, no more than three ATCA shelves are used to process the signal from approximately 34,000 channels. Given that modern technologies have been used compared to the previous system, all the monitoring and control infrastructure is being adapted and commissioned as well. This contribution presents the challenges of the installation, the commissioning and the milestones still to be completed towards the full operation of both the legacy and the new readout paths for the LHC Run 3.

RADiCAL—Precision Timing, Ultracompact, Radiation-Hard Electromagnetic Calorimetry

To address the challenges of providing high-performance calorimetry in future hadron collider experiments under conditions of high luminosity and high radiation (FCC-hh environments), we conducted R&D on advanced calorimetry techniques suitable for such operation, based on scintillation and wavelength-shifting technologies and photosensor (SiPM and SiPM-like) technology. In particular, we focused our attention on ultra-compact radiation-hard EM calorimeters based on modular structures (RADiCAL modules) consisting of alternating layers of the very dense absorber and scintillating plates, read out via radiation hard wavelength shifting (WLS) solid fiber or capillary elements to photosensors positioned either proximately or remotely, depending upon their radiation tolerance. RADiCAL modules provide the capability to measure simultaneously and with high precision the position, energy and timing of EM showers. This paper provides an overview of the instrumentation and photosensor R&D associated with the RADiCAL program.

Ultrafast PWO scintillator for future high energy physics instrumentation

The development of lead tungstate scintillator with the scintillation decay decreased down to the subnanosecond domain is reported. The material exhibits a scintillation decay with a time constant of 640 ps at a light yield of 7 phe/MeV and a high radiation tolerance to the electromagnetic component of ionizing radiation. It is shown to be an outstanding candidate for dual readout of scintillation and Cherenkov photons in electromagnetic calorimetry at future collider experiments.

SIMULATION STUDIES OF THE MOLIERE RADIUS FOR EM CALORIMETER MATERIALS

The Monte-Carlo calculations of the Moliere radius (RM) for some homogeneous and heterogeneous media used in electromagnetic calorimetry in the energy range from 50 MeV to 10 GeV are presented in detail. The obtained results, the uncertainties in determining RM, estimations of the absorbed energy, methods for approximating the absorbed energy, and the accuracy of the results are discussed as well. Some RM are shown for calorimeter proto-types of the Spin Physics Detector experiment (SPD). A one-parameter function of the Moliere radius dependence on the absorber-scintillator thickness ratio is obtained.

PWO based electromagnetic calorimetry to operate at a low temperature

The degradation of the optical transmittance under ionising radiation of the scintillation crystal in the scintillation spectral range leads to the losses of the light output, which results in the deterioration of the energy resolution and limits the operation time of the calorimeter made of the scintillator. This effect is especially prominent for calorimeters operating at a low temperature. The use of a lead tungstate scintillation crystal PbWO4 in calorimetry at a low temperature in the range from –20 to –45 °C provides a threefold increase in its scintillation yield, which causes a significant improvement in the energy resolution in the range up to 10 MeV. Keep on this feature is critically important for hadron spectroscopy. However, as the temperature of the PbWO4 crystal is lowered, the rate of spontaneous relaxation of colour centers created under ionising radiation significantly slows down, which shifts the dynamic level of the induced absorption towards a higher value under long-term irradiation of high-energy physics experiments. A comparison is made of the spontaneous relaxation of induced absorption in the spectral region of scintillations with stimulated relaxation upon irradiation of samples by infrared photons of different wavelengths. It is shown that the relaxation of colour centers can be accelerated up to one thousand times. Thus, recovery stimulation allows fast and efficient in situ recovery of the crystal optical transmittance either at beam-off periods or online at data acquisition. The application can substantially improve or extend the running period of the PWO based calorimeters at low temperatures by keeping the radiation damage at a tolerable level.

CALCULATION OF THE MOLIÈRE RADIUS FOR VARIOUS CONFIGURATIONS OF AN ELECTROMAGNETIC SAMPLING CALORIMETER ECaL SPD NICA

One of the main tasks of the electromagnetic calorimetry of the SPD setup is effective π0-γ separation in the energy range from 50 MeV to 10 GeV. Therefore, the current task is to optimize the design of the module cells in order to improve the physical parameters of the ECaL calorimeter. The Molière radius is determined in this work by the Monte Carlo method using Geant4 toolkit for various cell configurations of the calorimeter module. The results obtained in this work will be taken into account in the further development of the detecting systems of the ECaL SPD NICA.

Commissioning the ATLAS Liquid Argon Calorimeter Phase-I Upgrade

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region η < 3.2, and for hadronic and forward calorimetry in the region from η = 1.5 to η = 4.9. In the first LHC run (Run-1), a total luminosity of around 26 fb-1 was collected at centre-of-mass energies of 7-8 TeV. After detector consolidation during a long shut-down, Run-2 started in 2015 and around 150 fb-1 of data at a centre-of-mass energy of 13 TeV was recorded. With the end of Run-2 in 2018, a multi-year shutdown for the Phase-I detector upgrades began. As part of the Phase-I upgrade, new trigger readout electronics of the ATLAS LAr Calorimeter have been developed. Installation be-gan at the start of the LHC shut down in 2019 and is expected to be completed in 2020. A commissioning cam-paign is underway in order to realise the capabilities of the new, higher granularity and higher precision level-1 trigger hardware in Run-3 data taking. This contribution will give an overview of the new trigger readout system and the ongoing commissioning and installation efforts.

New perspectives on segmented crystal calorimeters for future colliders

Crystal calorimeters have a long history of pushing the frontier on high-resolution electromagnetic (EM) calorimetry for photons and electrons. We explore in this paper major innovations in collider detector performance that can be achieved with crystal calorimetry when longitudinal segmentation and dual-readout capabilities are combined with a new high EM resolution approach to Particle Flow in multi-jet events, such as e+e+→ HZ events in all-hadronic final-states at Higgs factories. We demonstrate a new technique for pre-processing π0 momenta through combinatoric di-photon pairing in advance of applying jet algorithms. This procedure significantly reduces π0 photon splitting across jets in multi-jet events. The correct photon-to-jet assignment efficiency improves by a factor of about 3 when the EM resolution is improved from 15 to 3%/√E. In addition, the technique of bremsstrahlung photon recovery significantly improves electron momentum measurements. A high EM resolution calorimeter increases the Z boson recoil mass resolution in Higgstrahlung events for decays into electron pairs to 80% of that for muon pairs. We present the design and optimization of a highly segmented crystal detector concept that achieves the required energy resolution of 3%/√E, and a time resolution better than 30 ps providing exceptional particle identification capabilities. We demonstrate that, contrary to previous detector designs that suffered from large neutral hadron resolution degradation from one interaction length of crystals in front of a sampling hadron calorimeter, the implementation of dual-readout on crystals permits to achieve a resolution better than 30%/√E⊕ 2% for neutral hadrons. Our studies find that the integration of crystal calorimetry into future Higgs factory collider detectors can open new perspectives by yielding the highest level of combined EM and neutral hadron resolution in the PFA paradigm.

A reconfigurable CMOS sensor for tracking, pre-shower and digital electromagnetic calorimetry

Recent advances in CMOS imaging sensor technology have led to designs able to withstand much higher radiation levels, up to those required at hadron colliders for all but the innermost layers. Also, with stitching, wafer scale devices have been fabricated on the same process as used for the prototypes described in this submission, for applications such as, for example, direct electron detection in transmission electron microscopy. A small sensor prototype has been designed and fabricated in the TowerJazz 180 nm CMOS imaging process. The prototype has a pixel matrix of 64x64 pixels with a pitch of 55 x 55μm and reads out using fast logic at 40 MHz. Each pixel contains four collection electrodes, trimming logic, pre-amplifier, shaper and discriminator with digital output. It can be reconfigured to function as either a binary short strip sensor, for particle tracking including as a pre-shower, or as a pad sensor, counting the number of pixels above threshold for digital calorimetry. As well as providing a seamless transition from outer tracking to EM calorimetry, for optimal use of particle flow algorithms, digital calorimetry also can give excellent energy resolution. This concept is proposed as a possible option for future digital calorimeters able to read-out at LHC collision rates with good radiation hardness and realisable in low cost commercial technologies for equipping large areas. Results on physics performance simulation in a FCC-hh context and the characterisation of the prototype sensor are presented. The summing logic is demonstrated and the analogue pixel performance is validated by illuminating a test pixel within the matrix with a laser of wavelength of 1064 nm. The absolute laser intensity is calibrated such that the injected charge is similar to that expected for a minimum ionising particle. The measured pre-amplifier and shaper signals are compared to Cadence simulations. Laser illuminations in the digital pixel area and the response measured using a threshold scan confirm successful digital functionality in strip and pad operation modes.

ATLAS LAr calorimeter performance in LHC Run 2

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudorapidity region |η| < 3.2, and for hadronic and forward calorimetry in the region from |η| = 1.5 to |η| = 4.9. In the first LHC run a total luminosity of 27 fb−1 has been collected at center-of-mass energies of 7–8 TeV. After detector consolidation during a long shutdown, Run 2 started in 2015 and 147 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. In order to realize the level-1 trigger acceptance rate of 100 kHz in Run 2 data taking, the number of read-out samples recorded and used for the energy and the time measurement has been modified from five to four while keeping the expected performance. The well calibrated and highly granular LAr calorimeter reached its design values both in energy measurement as well as in direction resolution. This contribution gives an overview of the detector operation, hardware improvements, changes in the monitoring and data quality procedures, to cope with increased pileup, as well as the achieved performance, including the calibration and stability of the electromagnetic scale, noise level, response uniformity and time resolution.

ATLAS LAr Calorimeter performance in LHC Run 2

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry and for hadronic and forward calorimetry in the region 1.5 < |η| < 4.9. In the first LHC run a total luminosity of 27 fb−1 has been collected at center-of-mass energies of 7–8 TeV . After detector consolidation during a long shutdown, Run-2 started in 2015 and 139 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. In order to accomplish the Level-1 acceptance rate of 100 kHz in Run-2 data taking, the number of read-out samples recorded and used for the energy and the time measurement has been modified from five to four while keeping the expected performance. The well calibrated and highly granular LAr Calorimeter reached its design goals, both in terms of energy and direction measurement. This contribution gives an overview of the detector operation, hardware improvements, monitoring and data quality procedures, as well as the achieved performance, including the calibration and stability of the electromagnetic scale, noise level, response uniformity and time resolution.

Scintillating crystals for the Neutral Particle Spectrometer in Hall C at JLab

This paper discusses the quality and performance of currently available PbWO4 crystals of relevance to high-resolution electromagnetic calorimetry, e.g. detectors for the Neutral Particle Spectrometer at Jefferson Lab or those planned for the Electron–Ion Collider. Since the construction of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) and early PANDA (The antiProton ANnihilations at DArmstadt) electromagnetic calorimeter (ECAL) the worldwide availability of high quality PbWO4 production has changed dramatically. We report on our studies of crystal samples from SICCAS/China and CRYTUR/Czech Republic that were produced between 2014 and 2019.

First tests of a reconfigurable depleted MAPS sensor for digital electromagnetic calorimetry

Digital Electromagnetic CALorimetry relies on a highly granular detector where the cell size is sufficiently small so that only a single particle in a shower enters each cell within a single readout cycle. The DECAL sensor, a depleted monolithic active pixel sensor (DMAPS), has been proposed as a possible technology for future digital calorimeters. A DECAL sensor prototype has been designed and fabricated in the TowerJazz 180 nm CMOS imaging process, using a high resistivity 18 μm epitaxial Si layer. The prototype has a pixel matrix of 64 × 64 pixels with a pitch of 55 × 55 μm, and is read out using fast logic at 40 MHz. It can be configured to function as either a strip sensor, for particle tracking, or a pad sensor, counting the number of pixels above threshold for digital calorimetry. Preliminary results of chip characterisation, including digital summing logic, analogue pixel performance and threshold scans under laser illumination are presented.

ATLAS LAr calorimeter performance in LHC run 2 and electronics upgrades for next runs

Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region |η|<3.2, and for hadronic and forward calorimetry in the region from |η|=1.5 to |η|=4.9. In the LHC Run 2 about 150 fb−1 of data at a center-of-mass energy of 13 TeV have been recorded. The well calibrated and highly granular LAr Calorimeter reached its design values both in energy measurement as well as in direction resolution. Electronics developments are pursued for the trigger readout of the ATLAS LAr Calorimeter towards the Phase-I upgrade scheduled in the LHC shut-down period between December 2018 and early 2021. Trigger signals with finer spatial granularity and higher precision are needed in order to improve the identification efficiencies of electrons, photons, taus, jets and missing energy, at high background rejection rates, already at the Level-1 trigger. Following new TDAQ buffering requirements and high expected radiation doses in the pileup conditions of the high-luminosity LHC, the LAr Calorimeter electronics will be further upgraded (Phase-II) to readout the full 182,500 calorimeter cells at 40 MHz with 16 bit dynamic range. Developments of low-power preamplifiers and shapers to meet these requirements are ongoing in 130 nm CMOS. In order to digitize the analogue signals on two gains after shaping, radiation-hard, low-power 40 MHz 14-bit ADCs are developed using a SAR architecture in 65 nm CMOS. This contribution gives an overview of the detector operation, changes in the monitoring and data quality procedures, to cope with increased pileup, as well as the achieved performance. Results of ASIC developments including quality assurance and quality control (QA/QC) and radiation hardness evaluations, performances of the pre-production boards and results of the system integration tests, progress of QA/QC of final production boards are presented along with the overall system design for the Phase-I upgrade. Results of tests of the first prototypes of front-end components are presented, along with design studies on the performance of the off-detector readout system for the Phase-II upgrade.

A highly granular calorimeter concept for long baseline near detectors

Future long baseline neutrino experiments such as the DUNE experiment under construction at Fermilab will perform precision measurements of neutrino oscillations, including the potential for the discovery of CP violation in the lepton sector. These measurements require an understanding of the unoscillated neutrino beam with unprecedented accuracy. This will be provided by complex near detectors which consist of different subsystems including tracking elements and electromagnetic calorimetry. A high granularity in the calorimeter, provided by scintillator tiles with SiPM readout as used in the CALICE analog hadron calorimeter, provides the capability for direction reconstruction of photon showers, which can be used to determine the decay positions of neutral pions. This can enable the association of neutral pions to neutrino interactions in the tracker volume, improving the event reconstruction of the near detector. Beyond photon and electron reconstruction, the calorimeter also provides sensitivity to neutrons. In this presentation, we will discuss a simulation study exploring the potential of high granularity for the electromagnetic calorimeter of the DUNE near detector. Particular emphasis will be placed on the combination with a high pressure TPC as tracking detector, which puts particularly stringent requirements on the calorimeter. The dependence of the projected detector performance on granularity, absorber material and absorber thickness as well as geometric arrangement satisfying the constraints of the TPC are explored.