Trigger Algorithms Research Articles

ATLAS Trigger and DAQ Upgrades for High-Luminosity LHC

The ATLAS Trigger-DAQ system will be significantly upgraded to explore new physics beyond the standard model in the High-Luminosity LHC environment with instantaneous luminosity of up to 7.5⨯1034 cm -2 s-1 . Two general trigger schemes are under study and their prospects and concerns are discussed. The muon trigger and readout electronics will be totally replaced to cope with a longer latency and a higher trigger rate. At the same time, new trigger algorithms using the precision tracker will be introduced to sharpen efficiency turn-ons and suppress fake triggers. The algorithm and the expected performance of the muon trigger are described. The hardware based track trigger is one of the major items introduced in the upgrade program. It will improve the trigger performance of various trigger items with a combination of the calorimeter or muon signature. The procedure for processing track information and an expected performance on the electron trigger are presented.

MEMS-based seismic intensity instrument for earthquake early warning

Micro-electro-mechanical systems (MEMS)-based tri-axial seismometer can be employed to design intensity instrument and construct early warning network. Using average period τc and peak amplitude of displacement Pd methods, the estimation relationships between seismometer and magnitude can be calculated. This work outlines the algorithm and first-hand experience using low-cost MEMS-based seismometer in seismic intensity instrument. τc and Pd methods are employed to calculate magnitude estimation and STA/LTA trigger algorithm is used to identify seismic event. A set of simulated earthquake wave experiments on a horizontal vibration table are used to testify the ability of P-wave identification. The results show that the accuracy of P-wave identification and seismic intensity judgement is over 95%, which proves the usability of improving implementations for the MEMS-based seismometer in the earthquake early warning application.

Application of Electronic Algorithms to Improve Diagnostic Evaluation for Bladder Cancer.

Strategies to ensure timely diagnostic evaluation of hematuria are needed to reduce delays in bladder cancer diagnosis. To evaluate the performance of electronic trigger algorithms to detect delays in hematuria follow-up. We developed a computerized trigger to detect delayed follow-up action on a urinalysis result with high-grade hematuria (>50 red blood cells/high powered field). The trigger scanned clinical data within a Department of Veterans Affairs (VA) national data repository to identify all patient records with hematuria, then excluded those where follow-up was unnecessary (e.g., terminal illness) or where typical follow-up action was detected (e.g., cystoscopy). We manually reviewed a randomly-selected sample of flagged records to confirm delays. We performed a similar analysis of records with hematuria that were marked as not delayed (non-triggered). We used review findings to calculate trigger performance. Of 310,331 patients seen between 1/1/2012-12/31/2014, the trigger identified 5,857 patients who experienced high-grade hematuria, of which 495 experienced a delay. On manual review of 400 randomly-selected triggered records and 100 non-triggered records, the trigger achieved positive and negative predictive values of 58% and 97%, respectively. Triggers offer a promising method to detect delays in care of patients with high-grade hematuria and warrant further evaluation in clinical practice as a means to reduce delays in bladder cancer diagnosis.

Design and performance of the phase I upgrade of the CMS Global Trigger

The Global Trigger is the final decision stage of the Level-1 Trigger of the CMS Experiment at the LHC. Previously implemented in VME, it has been redesigned and completely rebuilt in MicroTCA technology, using the Virtex-7 FPGA chip family. This allows implementing trigger algorithms close to the final analysis selection, combining different physical objects. The flexible and compact new system is presented, together with performance tests at a proton-proton centre-of-mass energy of 13 TeV. Firmware and software developments for the operation and validation of the Global Trigger will also be discussed.

Performance of the ATLAS Hadronic Tile Calorimeter in Run-2 and its Upgrade for the High Luminosity LHC

The Tile Calorimeter (TileCal) of the ATLAS experiment at the LHC is the central hadronic calorimeter designed for energy reconstruction of hadrons, jets, tauparticles and missing transverse energy. TileCal is a scintillator-steel sampling calorimeter and it covers the region of pseudo-rapidity up to 1.7, with almost 10000 channels measuring energies ranging from ∼30 MeV to ∼2 TeV. Each stage of the signal production, from scintillation light to the signal reconstruction, is monitored and calibrated. The performance of the Tile calorimeter has been studied in-situ employing cosmic ray muons and a large sample of proton-proton collisions, acquired during the operations of the LHC. Prompt isolated muons of high momentum from electroweak bosons decays are employed to study the energy response of the calorimeter at the electromagnetic scale. The calorimeter response to hadronic particles is evaluated with a sample of isolated hadrons. The modelling of the response by the Monte Carlo simulation is discussed. The calorimeter timing calibration and resolutions are studied with a sample of multijets events. Results on the calorimeter operation and performance are presented, including the calibration, stability, absolute energy scale, uniformity and time resolution. TileCal performance satisfies the design requirements and has provided an essential contribution to physics results in ATLAS.The Large Hadron Collider (LHC) has envisaged a series of upgrades towards a High Luminosity LHC (HL-LHC), delivering five times the LHC nominal instantaneous luminosity. The ATLAS Phase II upgrade, in 2024, will accommodate the detector and data acquisition system for the HL-LHC. In particular, the Tile Calorimeter will undergo a major replacement of its on- and off-detector electronics. All signals will be digitised and then transferred directly to the off-detector electronics, where the signals will be reconstructed, stored, and sent to the first level of trigger at a rate of 40 MHz. This will provide better precision for the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. Changes to the electronics will also contribute to the reliability and redundancy of the system. Three different front-end options are presently being investigated for the upgrade. Results of extensive laboratory tests and with beams of the three options will be presented, as well as the latest results on the development of the power distribution and the off-detector electronics.

The Run-2 ATLAS Trigger System

The ATLAS trigger successfully collected collision data during the first run of the LHC between 2009-2013 at different centre-of-mass energies between 900 GeV and 8TeV. The trigger system consists of a hardware Level-1 and a software-based high level trigger (HLT) that reduces the event rate from the design bunch-crossing rate of 40 MHz to an average recording rate of a few hundred Hz. In Run-2, the LHC will operate at centre-of-mass energies of 13 and 14 TeV and higher luminosity, resulting in up to five times higher rates of processes of interest. A brief review of the ATLAS trigger system upgrades that were implemented between Run-1 and Run-2, allowing to cope with the increased trigger rates while maintaining or even improving the efficiency to select physics processes of interest, will be given. This includes changes to the Level-1 calorimeter and muon trigger systems, the introduction of a new Level-1 topological trigger module and the merging of the previously two-level HLT system into a single event processing farm. A few examples will be shown, such as the impressive performance improvements in the HLT trigger algorithms used to identify leptons, hadrons and global event quantities like missing transverse energy. Finally, the status of the commissioning of the trigger system and its performance during the 2015 run will be presented.

The design and performance of the ATLAS Inner Detector trigger for Run 2 LHC Collisions at √s=13 TeV

The design and performance of the ATLAS Inner Detector trigger algorithms running online on the High Level Trigger processor farm with the LHC Run 2 data with collisions at both 50 ns and 25 ns are discussed. The HLT Inner Detector tracking algorithms are essential for the identification of nearly all physics signatures in the ATLAS trigger system. In order to deal with the expected higher rates for LHC Run 2, the Inner Detector trigger was redesigned during the 2013-15 long shutdown to satisfy the demands of the higher energy LHC operation. The detailed performance of the tracking algorithms with the Run 2 data taken in 2015 for the different trigger signatures in terms of both efficiency, and resolution is presented. The online processing times for running trigger tracking for the different trigger signatures are discussed in detail. Where appropriate, comparisons are made between the new strategies for Run 2, and the strategies adopted previously in Run 1. These comparisons demonstrate successful application and superior performance of the strategies adopted for Run 2.

ECG Triggering in Ultra-High Field Cardiovascular MRI

Cardiac magnetic resonance imaging at ultra-high field (B0 ≥ 7 T) potentially provides improved resolution and new opportunities for tissue characterization. Although an accurate synchronization of the acquisition to the cardiac cycle is essential, electrocardiogram (ECG) triggering at ultra-high field can be significantly impacted by the magnetohydrodynamic (MHD) effect. Blood flow within a static magnetic field induces a voltage, which superimposes the ECG and often affects the recognition of the R-wave. The MHD effect scales with B0 and is particularly pronounced at ultra-high field creating triggering-related image artifacts. Here, we investigated the performance of a conventional 3-lead ECG trigger device and a state-of-the-art trigger algorithm for cardiac ECG synchronization at 7 T. We show that by appropriate subject preparation and by including a learning phase for the R-wave detection outside of the magnetic field, reliable ECG triggering is feasible in healthy subjects at 7 T without additional equipment. Ultra-high field cardiac imaging was performed with the ECG signal and the trigger events recorded in 8 healthy subjects. Despite severe ECG signal distortions, synchronized imaging was successfully performed. Recorded ECG signals, vectorcardiograms, and large consistency in trigger event spacing indicate high accuracy for R-wave detection.

Synchronization of multiple USB 3.0 devices using Isochronous Timestamp Packet

In test and measurement, synchronizing multiple devices to timely coordinate data acquisition is crucial. This is due to the limited number of channels on a single device and the need for mixed-signal channels. Currently, various techniques have been proposed for triggering and synchronization among multiple devices such as GPIB, VXI, PXI/PXIe and LXI. However, they are expensive and need large footprint and additional cable or hardware to set up. Due to that, with the low cost and easy-to-setup USB 2.0, it is enhanced to have synchronization ability. There are various synchronization methods in USB 2.0 such as software-timed trigger, external hardware trigger and USB-inSync. The software-timed trigger is purely implemented in software and has high trigger delay, which is up to microseconds. Besides that, for both external hardware trigger and USB-inSync, they can achieve up to nanoseconds of synchronization precision. However, both of those methods need extra hardware or setup to synchronize multiple devices. In this paper, to overcome the drawbacks from the existing techniques, a trigger algorithm is proposed based on the study of USB 3.0 technology. The Isochronous Timestamp Packet (ITP) in USB 3.0 is used as the main component in the trigger algorithm. Without any hardware implementation, the trigger algorithm is able to trigger multiple USB 3.0 devices with a trigger delay around 200ns. In addition, the trigger algorithm can support up to maximum to three consecutive connected hubs without affecting the performance. In conclusion, the trigger algorithm increases the performance of synchronization of multiple USB device with only software intervention.

Level Zero Trigger Processor for the ultra rare kaon decay experiment: NA62

The NA62 experiment is designed to measure the (ultra-)rare decay K+→π+νν¯ branching ratio with a precision of ∼10% at the CERN Super Proton Synchrotron (SPS). The L0 Trigger Processor (L0TP) is the lowest level system of the trigger chain. It is hardware implemented using programmable logic. The architecture of the L0TP is completely new for a high energy physics experiment. It is fully digital, based on a standard gigabit ethernet communication between detectors and L0TP Board. The L0TP Board is a commercial development board, Terasic DE4, mounting an Altera Stratix IV FPGA. The primitives generated by sub-detectors are sent asynchronously using the UDP protocol to the L0TP during the entire beam spill period (about 5 seconds). The L0TP realigns in time the primitives coming from 7 different sources and manages the information of the time plus all the characteristics of the event as energy, multiplicity and position of hits in order to select good events with a comparison with preset masks. It should guarantee a maximum latency of 1ms. The maximum input rate is 10MHz for each sub-detector, while the design maximum output trigger rate is 1MHz. A complete trigger-less parasitic acquisition of the primitives is possible using mirroring switches to monitor the L0 behavior. A first version of the L0TP was commissioned during the 2014 NA62 pilot run and it is used in the current data taking. A description of the trigger algorithm is here presented.

Graphical processors for HEP trigger systems

General-purpose computing on GPUs is emerging as a new paradigm in several fields of science, although so far applications have been tailored to employ GPUs as accelerators in offline computations. With the steady decrease of GPU latencies and the increase in link and memory throughputs, time is ripe for real-time applications using GPUs in high-energy physics data acquisition and trigger systems. We will discuss the use of online parallel computing on GPUs for synchronous low level trigger systems, focusing on tests performed on the trigger of the CERN NA62 experiment. Latencies of all components need analysing, networking being the most critical. To keep it under control, we envisioned NaNet, an FPGA-based PCIe Network Interface Card (NIC) enabling GPUDirect connection. Moreover, we discuss how specific trigger algorithms can be parallelised and thus benefit from a GPU implementation, in terms of increased execution speed. Such improvements are particularly relevant for the foreseen LHC luminosity upgrade where highly selective algorithms will be crucial to maintain sustainable trigger rates with very high pileup.

Integrated Optimization of Long-Range Underwater Signal Detection, Feature Extraction, and Classification for Nuclear Treaty Monitoring

We designed and jointly optimized an integrated signal processing chain for detection and classification of long-range passive-acoustic underwater signals recorded by the global geophysical monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization. Starting at the level of raw waveform data, a processing chain of signal detection, feature extraction, and signal classification was designed and jointly optimized to the task. Relevant waveform segments were in a first step identified by a generic, flexibly parameterized detection algorithm on a long- to short-term averages' ratio of the spectral energy. For representation, general-purpose sound processing features, with an added focus on spectral and cepstral features, were extracted from the detected segments. As classifiers, support vector machines with different kernel functions were employed alongside other baseline learning algorithms. The free parameters of the overall toolchain (i.e., trigger algorithm parameters and classifier hyperparameters) were jointly optimized in a cross-validation setting, either according to the cross-validation classification error or the cross-validation area under the receiver operating characteristic curve. Experiments demonstrate that our method outperforms machine learning algorithms task-tailored to a previous, human-expert-designed preprocessing chain. The presented approach can be adapted to a wide range of problems that can benefit from jointly optimizing parameters of preprocessing and classification algorithm.

Upgrade of the ATLAS Tile hadronic calorimeter for high-luminosity LHC run

The ATLAS Tile Calorimeter (TileCal) will undergo a major replacement of its on- and off-detector electronics for the Long Shutdown 3 that is planned for 2024 and 2025. All signals will be digitised and transferred directly to the off-detector electronics, where the signals are reconstructed, stored, and sent to the first level of trigger at a rate of 40MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. Changes to the electronics will also contribute to the reliability and redundancy of the system. Three different front-end options are presently being investigated for the upgrade and will be chosen after extensive test beam studies. A Hybrid Demonstrator module has been developed. The demonstrator is undergoing extensive testing and is planned for insertion in ATLAS.

Trigger algorithm of vehicle automatic crash notification system

The Automatic Crash Notification (ACN) system is an effective technology to decrease the crash response time, improve the level of post-accident rescue and alleviate the severity of injuries. To realize this system, a vehicle terminal is developed. And based on a moving window integral algorithm, the trigger algorithm of ACN system is designed. By comparing the effect of different window widths on the trigger algorithm, we select the window width of the moving window integral algorithm as 8 ms. After system is triggered, different notify types was determined according to the change of velocity in the moving window. A sled impact simulation test shows that the impact can be identified rapidly and also the notify types can be judged by the trigger algorithm. A vehicle road test proves that the ACN system has no false trigger cases. The outcomes of this study support identifications of accidents and crash severities for both occupants and emergency centers.

Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment

This article gives an overview of the steps taken in ATLAS to identify hadronically decaying tau leptons and to validate the performance. The tau trigger, the reconstruction and identification algorithms, and the energy calibration are described. The performance is tested with Z→ττ events, collected in 2012 at 8 TeV center-of-mass energy of the LHC. Identification efficiencies are determined both in real data and simulation and differences are expressed in terms of correction factors, with uncertainties below 6%. The uncertainty on the energy scale is measured with two independent methods and found to be less than 4%. All algorithms show good stability against a varying number of simultaneous proton-proton collisions.

The ATLAS FTK system: how to improve the physics potential with a tracking trigger

After a very successful data taking run, the ATLAS experiment is being upgraded to cope with the higher luminosity and higher center of mass energy that the Large Hadron Collider (LHC) will provide in the next years. The Fast Tracker (FTK) trigger system, part of the ATLAS trigger upgrade program, is a highly parallel hardware device processor based on a mixture of advanced technologies. FTK provides global track reconstruction in the full inner silicon detector, with resolution comparable to the offline algorithms, in approximately 100 microseconds, allowing a fast and precise detection of the primary and secondary vertex information. The track and vertex information is then used by the high-level trigger algorithms, allowing highly improved trigger performance for the most difficult signatures, such as b-jets. The expected physics performance of FTK in the harsh environment at high pile-up and high luminosities at LHC Run2 are presented.

NaNet-10: a 10GbE network interface card for the GPU-based low-level trigger of the NA62 RICH detector.

A GPU-based low level (L0) trigger is currently integrated in the experimental setup of the RICH detector of the NA62 experiment to assess the feasibility of building more refined physics-related trigger primitives and thus improve the trigger discriminating power. To ensure the real-time operation of the system, a dedicated data transport mechanism has been implemented: an FPGA-based Network Interface Card (NaNet-10) receives data from detectors and forwards them with low, predictable latency to the memory of the GPU performing the trigger algorithms. Results of the ring-shaped hit patterns reconstruction will be reported and discussed.

A high bandwidth and versatile advanced MC board

Nowadays, the trigger and data acquisition (TDAQ) system of many particle physics experiments always require larger data throughput, larger number of high speed I/Os and much more sophisticated trigger algorithms with longer latency. The micro-TCA and the ATCA standards, with their FPGA-based boards, respond to those requirements. Besides, maintenance of the electronics may become an issue and it is therefore of interest to limit the use of many different custom-made electronics boards. So it is significant to develop a high bandwidth and versatile board. In this contribution we present a new AMC board based on AMC.0, named as Trigger Receiver Board (TRB).

The upgrade of the CMS Global Trigger

The Global Trigger is the final step of the CMS Level-1 Trigger. Previously implemented in VME, it has been redesigned and completely rebuilt in MicroTCA technology, using the Virtex-7 FPGA chip family. It will allow to implement trigger algorithms close to the final physics selection. The new system is presented, together with performance tests undertaken in parallel operation with the legacy system during the initial months of Run II of the LHC at a beam energy of 13 TeV.

Trigger algorithms and electronics for the ATLAS muon new small wheel upgrade

The New Small Wheel Upgrade for the ATLAS experiment will replace the innermost station of the Muon Spectrometer in the forward region in order to maintain its current performance during high luminosity data-taking after the LHC Phase-I upgrade. The New Small Wheel, comprising Micromegas and small Thin Gap Chambers, will reduce the rate of fake triggers coming from backgrounds in the forward region and significantly improve the Level-1 muon trigger selectivity by providing precise on-line segment measurements with ∼ 1 mrad angular resolution. Such demanding precision, together with the short time (∼ 1 μs) to prepare trigger data and perform on-line reconstruction, implies very stringent requirements on the design of trigger system and trigger electronics. This paper presents an overview of the design of the New Small Wheel trigger system, trigger algorithms and processor hardware.