Calorimeter Trigger Research Articles

Design of the CMS High Granularity Calorimeter trigger primitive generator system

The High Luminosity phase of the LHC (HL-LHC) is planned to begin data taking in 2029, with the instantaneous luminosity expected to increase to 4 times its current value and the average number of particle interactions per bunch crossing increasing by approximately 3.5 times its current value. The current endcap calorimeters in the CMS detector will be replaced by a novel high granularity calorimeter (HGCAL) that will have fine segmentation in both the transverse and longitudinal directions and will be the first such calorimeter specifically optimised for particle flow reconstruction to operate at a colliding-beam experiment. The Level 1 trigger of the CMS experiment will combine the calorimeter data with tracking information to allow particle-flow techniques to be used. The high granularity of the calorimeter leads to about six million readout channels in total, concentrated in one million trigger cells, sampled for the L1 trigger at a rate of 40 MHz. The trigger data volumes will be an order of magnitude above those currently handled in CMS, posing significant challenges for data manipulation and processing. In addition, the trigger algorithms must be able to efficiently reject the huge background rate in the forward region of the detector due to the high pileup environment. The status of the HGCAL trigger architecture and design, as well as the algorithms developed in order to tackled these major issues, is presented here. The data flow is described from the formation and preselection of trigger cells on detector to the generation of two types of trigger primitives off detector, projective towers of energy in the (η, ϕ) plane and three-dimensional clusters of particles. Particle flow will use these 3D clusters, and their formation is described and followed by recent developments in the optimization of their transverse size.

System Design and Prototyping of the CMS Level-1 Calorimeter Trigger at the High-Luminosity LHC

System Design and Prototyping of the CMS Level-1 Calorimeter Trigger at the High-Luminosity LHC

The NA62 level 0 calorimetric trigger fast readout implementation, commissioning and data taking performances

The NA62 experiment at the CERN SPS aims to measure the branching ratio of the very rare kaon decay . The Calorimetric Level 0 Trigger identifies clusters in the electromagnetic and hadronic calorimeters. Along with the trigger data sent to the L0 Trigger Processor, readout data is collected to be sent to the L1 software trigger. In this work we present the novel implementation of the readout data collection and forwarding system in the multiple layers of the calorimetric trigger structure. We will also present the commissioning of the system and the performance evaluation on current data taking.

A 40 MHz Level-1 trigger scouting system for the CMS Phase-2 upgrade

The CMS Phase-2 upgrade for the HL-LHC aims at preserving and expanding the current physics capability of the experiment under extreme pileup conditions. A new tracking system incorporates a track finder processor, providing tracks to the Level-1 (L1) trigger. A new high-granularity calorimeter provides fine-grained energy deposition information in the endcap region. New front-end and back-end electronics feed the L1 trigger with high-resolution information from the barrel calorimeter and the muon systems. The upgraded L1 will be based primarily on the Xilinx Ultrascale Plus series of FPGAs, capable of sophisticated feature searches with resolution often similar to the offline reconstruction. The L1 Data Scouting system (L1DS) will capture L1 intermediate data produced by the trigger processors at the beam-crossing rate of 40 MHz, and carry out online analyses based on these limited-resolution data. The L1DS will provide fast and virtually unlimited statistics for detector diagnostics, alternative luminosity measurements, and, in some cases, calibrations. It also has the potential to enable the study of otherwise inaccessible signatures, either too common to fit in the L1 trigger accept budget or with requirements that are orthogonal to “mainstream” physics. The requirements and architecture of the L1DS system are presented, as well as some of the potential physics opportunities under study. The first results from the assembly and commissioning of a demonstrator currently being installed for LHC Run-3 are also presented. The demonstrator collects data from the Global Muon Trigger, the Layer-2 Calorimeter Trigger, the Barrel Muon Track Finder, and the Global Trigger systems of the current CMS L1. This demonstrator, as a data acquisition (DAQ) system operating at the LHC bunch-crossing rate, faces many of the challenges of the Phase-2 system, albeit with scaled-down connectivity, reduced data throughput and physics capabilities, providing a testing ground for new techniques of online data reduction and processing.

ATLAS LAr calorimeter commissioning for LHC Run-3

To cope with the increase of the luminosity at Run-3 of the LHC, new trigger readout electronics have been installed on the Liquid Argon Calorimeters. More than 1500 boards of the legacy system were refurbished and re-installed, 124 new on-detector boards and 116 new back-end mezzanine cards equipped with large FPGAs were added to digitize the calorimeter trigger signals. All the monitoring and control infrastructure is being adapted and commissioned. These proceedings will present the challenges of the installation, the commissioning, and the works still to be completed toward the full operation of both the legacy and the digital trigger in the LHC Run-3.

The CMS Level-1 Calorimeter Trigger for the HL-LHC

The High-Luminosity LHC (HL-LHC) provides an opportunity for a pioneering physics program to harness an integrated luminosity of 4000 fb−1 of ten years of operations. This large volume of collision data will help in high precision measurements of the Standard Model (SM) and the search for new and rare physics phenomena. The harsh environment of 200 proton–proton interactions poses a substantial challenge in the collection of these large datasets. The HL-LHC CMS Level-1 (L1) trigger, including the calorimeter trigger, will receive a massive upgrade to tackle the challenge of a high-bandwidth and high pileup environment. The L1 trigger is planned to handle a very high bandwidth (∼63 Tb/s) with an output rate of 750 kHz, and the desired latency budget is 12.5 μs. The calorimeter trigger aims to process the high-granular information from the new end-cap detector called the high-granularity calorimeter (HGCAL) and the barrel calorimeter. The HL-LHC trigger prototyped boards are equipped with large modern-day FPGAs and high-speed optical links (∼28 Gb/s), which helps in the parallel and rapid computation of the calorimeter trigger algorithms. This article discusses the proposed design and expected performance of the upgraded CMS Level-1 calorimeter trigger system.

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.

Development, construction and tests of the Mu2e electromagnetic calorimeter mechanical structures

The “muon-to-electron conversion” (Mu2e) experiment at Fermilab will search for the charged lepton flavour violating neutrino-less coherent conversion of a muon into an electron in the field of an aluminum nucleus. The observation of this process would be the unambiguous evidence of the existence of physics beyond the standard model. Mu2e detectors comprise a straw-tracker, an electromagnetic calorimeter and an external veto for cosmic rays. In particular, the calorimeter provides excellent electron identification, a fast calorimetric online trigger, and complementary information to aid pattern recognition and track reconstruction. The detector has been designed as a state-of-the-art crystal calorimeter and employs 1348 pure Cesium Iodide (CsI) crystals readout by UV-extended silicon photosensors and fast front-end and digitization electronics. A design consisting of two identical annular matrices (named “disks”) positioned at the relative distance of 70 cm downstream the aluminum target along the muon beamline satisfies the Mu2e physics requirements. The hostile Mu2e operational conditions, in terms of radiation levels (total expected ionizing dose of 12 krad and a neutron fluence of 5 × 1010 n/cm2 @ 1 MeVeq (Si)/y), magnetic field intensity (1 T) and vacuum level (10−4 Torr) have posed tight constraints on scintillating materials, sensors, electronics and on the design of the detector mechanical structures and material choice. The support structure of each 674 crystal matrix is composed of an aluminum hollow ring and parts made of open-cell vacuum-compatible carbon fiber. The photosensors and front-end electronics for the readout of each crystal are inserted in a machined copper holder and make a unique mechanical unit. The resulting 674 mechanical units are supported by a machined plate of vacuum-compatible plastic material. The plate also integrates the cooling system made of a network of copper lines flowing a low temperature radiation-hard fluid and placed in thermal contact with the copper holders to constitute a low resistance thermal bridge. The data acquisition electronics are hosted in aluminum custom crates positioned on the external lateral surface of the disks. The crates also integrate the electronics cooling system as lines running in parallel to the front-end system. In this paper we report on the calorimeter mechanical structure design, the mechanical and thermal simulations that have determined the design technological choices, and the status of component production, quality assurance tests and plans for assembly at Fermilab.

Multiplexing Firmware Prototypes for the Global Trigger Subsystem of ATLAS Phase-II Upgrade

As part of the ATLAS experiment's Phase-II Upgrade, improved trigger hardware and algorithms will be implemented onto a single-level architecture. The global trigger (GT) subsystem is a new firmware (FW)-focused project designed to meet stringent requirements from the high-luminosity runs of the large hadron collider (LHC). The global multiplexer (MUX) is the input aggregating stage of the GT; it performs three main tasks: 1) aggregating data from several sources, connected with more than 2300 input fibers, under different protocols; 2) time-multiplexing the incoming data, to sort the packets per bunch-crossing (BC) events, by compensating the relative skews across the various serial input channels; and 3) transmitting, in a round-robin fashion, the sorted BC data to the global event processor (GEP) array, which is the following stage of the GT subsystem and is composed of 48 nodes, each one processing a single BC event. Two MUX FW prototypes for the Global Feature EXtractor (gFEX, part of the liquid argon calorimeter trigger) inputs have been designed, implemented, and validated on a gFEX production board, for up to 72 input and output channels. A four-channel version has been completed with I/O interfaces and validated in a full-chain design, accepting 8b/10b encoded inputs at 11.2 Gb/s and transmitting at 25.78125 Gb/s under Xilinx Aurora 64b/66b protocol. The total latency has been benchmarked in all of its contributing subcomponents and proven to meet the requirements from the Technical Design Report for the Phase-II Upgrade of the trigger and data acquisition system.

FELIX: the Detector Interface for the ATLAS Experiment at CERN

The Front-End Link eXchange (FELIX) system is an interface between the trigger and detector electronics and commodity switched networks for the ATLAS experiment at CERN. In preparation for the LHC Run 3, to start in 2022, the system is being installed to read out the new electromagnetic calorimeter, calorimeter trigger, and muon components being installed as part of the ongoing ATLAS upgrade programme. The detector and trigger electronic systems are largely custom and fully synchronous with respect to the 40.08 MHz clock of the Large Hadron Collider (LHC). The FELIX system uses FPGAs on server-hosted PCIe boards to pass data between custom data links connected to the detector and trigger electronics and host system memory over a PCIe interface then route data to network clients, such as the Software Readout Drivers (SW ROD), via a dedicated software platform running on these machines. The SW RODs build event fragments, buffer data, perform detector-specific processing and provide data for the ATLAS High Level Trigger. The FELIX approach takes advantage of modern FPGAs and commodity computing to reduce the system complexity and effort needed to support data acquisition systems in comparison to previous designs. Future upgrades of the experiment will introduce FELIX to read out all other detector components.

Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger

The PreProcessor of the ATLAS Level-1 Calorimeter Trigger prepares the analogue trigger signals sent from the ATLAS calorimeters by digitising, synchronising, and calibrating them to reconstruct transverse energy deposits, which are then used in further processing to identify event features. During the first long shutdown of the LHC from 2013 to 2014, the central components of the PreProcessor, the Multichip Modules, were replaced by upgraded versions that feature modern ADC and FPGA technology to ensure optimal performance in the high pile-up environment of LHC Run 2. This paper describes the features of the new Multichip Modules along with the improvements to the signal processing achieved.

Upgrade of the ATLAS Hadronic Tile Calorimeter for the High Luminosity LHC

The ATLAS hadronic Tile Calorimeter (TileCal) will undergo major upgrades to the on- and off-detector electronics in preparation for the high luminosity programme of the LHC (HL-LHC) in 2026. The system will cope with the HL-LHC increased radiation levels and out-of-time pileup. The on-detector electronics of the upgraded system will continuously digitize and transmit all photomultiplier signals to the off-detector systems at a 40 MHz rate. The off-detector electronics will store the data in pipeline buffers, reconstruct cell energy, produce digital hadronic cell sums of various granularity and send it to the Level-0 calorimeter trigger system, finally read out selected events. The modular front-end electronics feature radiation-tolerant commercial off-the-shelf components and redundant design to minimise single points of failure. The timing, control and communication interface with the off-detector electronics is implemented with modern Field Programmable Gate Arrays (FPGAs) and high speed fibre optic links running up to 9.6 Gb/s. The TileCal upgrade program has included extensive R&D and test beam studies using the beams from the Super Proton Synchrotron (SPS) accelerator at CERN. A Demonstrator module equipped with the novel electronics for the HL-LHC upgrade and compatible with the existing ATLAS read-out chain inserted in ATLAS in August 2019 for testing in actual detector conditions. We present the status of the upgrade program, the results using muon, electron and hadron beams at various incident energies and impact angles collected in 2015-2018, combined results of Demonstrator tests and calibration runs to evaluate the readiness of the new design.

Performance of the Belle II calorimeter trigger system at the SuperKEKB Phase 3 run

The Belle II experiment at the SuperKEKB electron-positron collider began physics data-taking in 2019 with full detectors. The main goal of the Belle II is to search for new physics beyond the Standard Model in heavy flavor decays and Dark sector. In order to select events of interest efficiently under severe beam background environment from higher instantaneous luminosity run than the KEKB collider, we have upgraded a real-time hardware trigger system using the CsI(Tl) electromagnetic calorimeter. In this report, performance of the calorimeter trigger system under SuperKEKB Phase 3 operation is described.

The Phase-I upgrade of the ATLAS Level-1 calorimeter trigger

The ATLAS Level-1 calorimeter trigger (L1Calo) is a hardware-based system that identifies events containing calorimeter-based physics objects, including electrons, photons, taus, jets, and missing transverse energy. In preparation for Run 3, when the LHC will run at higher energy and instantaneous luminosity, L1Calo is currently implementing a significant programme of planned upgrades. The existing hardware will be replaced by a new system of feature extractor (FEX) modules, which will process finer-granularity information from the calorimeters and execute more sophisticated algorithms to identify physics objects; these upgrades will permit better performance in a challenging high-luminosity and high-pileup environment.

First results on the performance of the PADME electromagnetic calorimeter

The PADME experiment, hosted at the Laboratori Nazionali di Frascati in Italy, is dedicated to the dark photon search. It looks for the reaction e+ e−arrow A′ γ, where A′ indicates the dark photon. The 550 MeV positrons beam that impinges on electrons, coming from an active diamond target, allows to scan A′ masses up to 23.7 MeV. In this context, the segmented electromagnetic calorimeter plays a fundamental role, since it measures the final photon four-momentum. It consists of 616 BGO crystals displaced in a cylindrical shape of ≈29 cm radius with a central square hole of 5 crystals side, to let Bremsstrahlung radiation pass, to limit the calorimeter trigger rate. Each crystal is read by a HZC XP1911 type B photomultipliers and their signal is digitised by means of a CAEN V1742 board, taking 1024 samples at 1 GS/S. Here we report in detail the solutions adopted for the calorimeter together with the results obtained in tests performed on a small prototype and on single scintillating units.

Progress on the Electromagnetic Calorimeter Trigger Simulation at the Belle II Experiment

The Belle II experiment at KEK in Japan has started real data taking from April 2018 to probe a New Physics beyond the Standard Model by measuring CP violation precisely and rare weak decays of heavy quark and lepton. The experiment is performed at the high luminosity SuperKEKB e^+ e^- collider with 80 x 10^34 cm^-2 s^-1 as an ultimate instantaneous luminosity. In order to develop and test an appropriate trigger algorithm under much higher luminosity and beam background environment than previous KEKB collider, a detail simulation study of the Belle II calorimeter trigger system is very crucial to operate Belle II Trigger and DAQ system in stable. We report preliminary results on various trigger logics and their efficiencies using physics and beam background Monte Carlo events with a Belle II Geant4-based analysis framework called Basf2.

Performance and quality control of a radiation-hard 12-bit 40 MSPS ADC for the ATLAS Liquid Argon calorimeter trigger readout electronics Phase-I upgrade at the LHC

A radiation-hard quad-channel 12-bit 40 MSPS pipeline analog-to-digital converter (ADC) has been designed for the trigger readout electronics Phase-I upgrade of the ATLAS Liquid Argon calorimeter, at the CERN Large Hadron Collider. The final version of the custom design, fabricated in a commercial 130 nm CMOS process, is presented and found to meet the system requirements for analog performance and radiation tolerance. The procedure for quality control of 17200 ADCs is described and the results are presented.

Development and data path integration test of the global Feature EXtractor for the ATLAS Level-1 calorimeter trigger system Phase-I upgrade

Abstract The global Feature Extractor (gFEX) is a component of the Phase-I upgrade of the Level-1 Calorimeter (L1Calo) trigger system for the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. The gFEX is used to identify patterns of energy associated with the hadronic decays of high momentum Higgs, W and Z bosons, top quarks, and exotic particles in real time at the 40 MHz LHC bunch crossing rate. Three prototypes were implemented and tested from 2014 to 2017. With the lessons learned from the prototypes, the final gFEX production board has been implemented at the end of 2017. The gFEX receives up to 300 fiber optical links from the calorimeter and transmits trigger data on 96 links to the ATLAS Level-1 Topological [1] (L1Topo) trigger at a rate of up to 12.8 Gb/s. There are also 24 electrical links on board for communication between two FPGAs running at speeds of up to 25.6 Gb/s. The hardware functionality and performance of the production board have been evaluated. A data path integration test between the Liquid Argon Digital Processing Blade (LDPB) [2] and the Front End LInk eXchange (FELIX) [3] was performed successfully at CERN in 2018.

Design of the CMS calorimeter trigger upgrade from Phase I to Phase II of the LHC

The CMS experiment implements a sophisticated two-level triggering system composed of the Level-1, instrumented by custom-design hardware boards, and the software High Level Trigger. In 2017, the LHC delivered proton-proton collisions at a centre-of-mass energy of 13 TeV with a peak instantaneous luminosity larger than 2×1034 cm−2s−1, more than twice the peak luminosity reached during Run I and far larger than the design value. The CMS Level-1 calorimeter trigger was upgraded during the long shutdown 1 between 2013 and 2015, to improve its performance at high luminosity and large number of simultaneous inelastic collisions per crossing (pile-up). All the electronic boards have been replaced, tested and commissioned with data. Smarter, more sophisticated, and innovative algorithms are now the core of the first decision layer of CMS: the upgraded trigger system implements dynamic clustering techniques, pile-up subtraction and isolation requirements for electrons and tau leptons. In addition, the new global trigger is capable of computing complex variables such as those involving the invariant mass of trigger objects. The trigger selections used for a wide variety of physics signals during Run II are presented, ranging from simple single-object selections to more sophisticated algorithms combining different objects and applying analysis-level reconstruction and selection. The design and operation of the Phase I calorimeter trigger will be reviewed. The technological choices made influenced the path towards the Phase II upgrade system necessary for the LHC run at a center-of mass energy of 14 TeV with luminosity of 5−7×1034 cm−2s−1, corresponding to 140-200 pile-up events. The addition of the tracker information at Level-1 and the enhanced calorimeter granularity will be used to maintain the trigger object thresholds at a similar level as the present system.

The ATLAS High-Level Calorimeter Trigger in Run-2

The ATLAS Experiment uses a two-level triggering system to identify and record proton-proton collision events containing a wide variety of physics signatures. It reduces the event rate from the bunch crossing rate of 40 MHz to an average recording rate of 1 kHz, whilst maintaining high efficiency for interesting collision events. It is composed of an initial hardware-based level-1 trigger followed by a software-based high-level trigger. A central component of the high-level trigger is the calorimeter trigger. This is responsible for processing data from the electromagnetic and hadronic calorimeters in order to identify electrons, photons, taus, jets and missing transverse energy. This paper presents the performance of the high-level calorimeter trigger in Run-2, noting the improvements that have been made in response to the challenges of operating at high luminosity.