Fast tracking for the second level trigger of the ATLAS experiment using silicon detectors data

To maintain sensitivity to new physics in the coming years of Large Hadron Collider (LHC) operations, A Toroidal LHC ApparatuS (ATLAS) collaboration has been working on upgrading a portion of the front-end (FE) electronics and replacing some parts of the detector with new devices that can operate under the much harsher background conditions of future LHC runs. The legacy FE of the ATLAS detector sent data to the data acquisition (DAQ) system via the so-called Read Out Drivers (RODs) custom-made VMEbus boards devoted to data processing, configuration, and control. The data were then received by the Read Out System (ROS), which was responsible for buffering them during the High-Level Trigger (HLT) processing. From Run 3 onward, all new trigger and detector systems will be read out using new components, replacing the combination of the ROD and the ROS. This new path will feature an application called the Software Read Out Driver (SW ROD), which will run on a commodity server receiving FE data via the Front-End Link eXchange (FELIX) system. The SW ROD will perform event fragment building and buffering as well as serving the data on request to the HLT. The SW ROD application has been designed as a highly customizable high-performance framework providing support for detector-specific event building and data processing algorithms. The implementation that will be used for Run 3 of the LHC is capable of building event fragments at a rate of 100 kHz from an input stream consisting of up to 120 MHz of individual data packets. This document will cover the design and the implementation of the SW ROD application and will present the results of performance measurements executed on the server models selected to host SW ROD applications during Run 3.

The purpose of this paper is to examine the model dependence of the stringent constraints on the gluino mass obtained from the Large Hadron Collider (LHC) experiments by analyzing the Run II data using specific simplified models based on several ad hoc sparticle spectra which cannot be realized even in the fairly generic pMSSM models. We first revisit the bounds on the gluino mass placed by the ATLAS collaboration using the [Formula: see text] data. We show that the exclusion region in the [Formula: see text] plane in the pMSSM scenario sensitively depends on the mass hierarchy between the left and right squarks and composition of the lighter electroweakinos and to a lesser extent, other parameters. Most importantly, for higgsino-type lighter electroweakinos (except for the LSP), the bound on the gluino mass from this channel practically disappears. However, if such models are confronted by the ATLAS [Formula: see text] data, fairly strong limits are regained. Thus, in the pMSSM, an analysis involving a small number of channels may provide more reliable mass limits. We have also performed detailed analyses on neutralino Dark Matter (DM) constraints in the models we have studied and have found that for a significant range of LSP masses, the relic density constraints from the WMAP/PLANCK data are satisfied and LSP-gluino coannihilation plays an important role in relic density production. We have also checked the simultaneous compatibility of the models studied here with the direct DM detection, and the LHC constraints.

Collisions of the Large Hadron Collider (LHC) were collected by ATLAS end of 2009 at a centre of mass energy of 900 GeV and are now being collected at √s = 7 TeV. This paper gives an overview of the performance of the ATLAS high level trigger for the selection of electrons, photons, taus, jets and missing transverse energy. Comparisons of the selection variables based on the calorimeter and tracking information calculated by the different trigger levels and the offline reconstruction are shown. This has been an important step in the commissioning of these triggers to ensure their correct functioning and the results from the first data are very encouraging. Furthermore, examples of comparisons between data and Monte Carlo simulations of some of the selection variables are presented. At the end a brief outlook will be given on the steps to be taken to fully commission these triggers with 7 TeV collision data.

The ATLAS trigger system includes a Level-1 (L1) trigger based on custom electronics and firmware, and a high-level software trigger running on off-the-shelf hardware. The L1 trigger system uses information from the forward detectors, the calorimeters and the muon trigger detectors. Once information from all muon trigger sectors has been received, trigger candidate multiplicities are calculated by the Muon-to-Central-Trigger-Processor Interface (MUCTPI). Muon multiplicity information is sent to the Central-Trigger-Processor (CTP) and trigger objects are sent to the L1 Topological Trigger Processor (L1Topo). The CTP combines the information received from the MUCTPI with the trigger information from the forward detectors, the calorimeters and the L1Topo, and takes the L1 trigger decision. As part of the ATLAS L1 trigger system upgrade for Run-3 of the Large Hadron Collider (LHC) a new MUCTPI has been designed and commissioned. We discuss the commissioning and operation of the new MUCTPI used in ATLAS from the beginning of Run-3. In particular, we describe the integration tests which have been carried out for the commissioning and operation of the new MUCTPI.

A Large Ion Collider Experiment (ALICE) is one of the four major experiments at the Large Hadron Collider (LHC) at CERN. The high level trigger (HLT) is a compute cluster, which reconstructs collisions as recorded by the ALICE detector in real-time. It employs a custom online data-transport framework to distribute data and workload among the compute nodes. ALICE employs subdetectors that are sensitive to environmental conditions such as pressure and temperature, e.g., the time projection chamber (TPC). A precise reconstruction of particle trajectories requires calibration of these detectors. Performing calibration in real time in the HLT improves the online reconstructions and renders certain offline calibration steps obsolete speeding up offline physics analysis. For LHC Run 3, starting in 2020 when data reduction will rely on reconstructed data, online calibration becomes a necessity. Reconstructed particle trajectories build the basis for the calibration making a fast online-tracking mandatory. The main detectors used for this purpose are the TPC and Inner Tracking System. Reconstructing the trajectories in the TPC is the most compute-intense step. We present several improvements to the ALICE HLT developed to facilitate online calibration. The main new development for online calibration is a wrapper that can run ALICE offline analysis and calibration tasks inside the HLT. In addition, we have added asynchronous processing capabilities to support long-running calibration tasks in the HLT framework, which runs event-synchronously otherwise. In order to improve the resiliency, an isolated process performs the asynchronous operations such that even a fatal error does not disturb data taking. We have complemented the original loop-free HLT chain with ZeroMQ data-transfer components. The ZeroMQ components facilitate a feedback loop that inserts the calibration result created at the end of the chain back into tracking components at the beginning of the chain, after a short delay. All these new features are implemented in a general way, such that they have use-cases aside from online calibration. In order to gather sufficient statistics for the calibration, the asynchronous calibration component must process enough events per time interval. Since the calibration is valid only for a certain time period, the delay until the feedback loop provides updated calibration data must not be too long. A first full-scale test of the online calibration functionality was performed during 2015 heavy-ion run under real conditions. Since then, online calibration is enabled and benchmarked in 2016 proton-proton data taking. We present a timing analysis of this first online-calibration test, which concludes that the HLT is capable of online TPC drift time calibration fast enough to calibrate the tracking via the feedback loop. We compare the calibration results with the offline calibration and present a comparison of the residuals of the TPC cluster coordinates with respect to offline reconstruction.

The ATLAS detector uses a real time selective triggering system to reduce the high interaction rate from 40 MHz to its data storage capacity of 1 kHz. A hardware first level (L1) trigger limits the rate to 100 kHz and a software high level trigger (HLT) selects events for offline analysis. The HLT uses the Regions of Interest (RoIs) identified by L1 and provided by the Region of Interest Builder (RoIB). The current RoIB is a custom VMEbus based system that operated reliably since the first run of the LHC . Since the LHC will reach higher luminosity and ATLAS will increase the complexity and number of L1 triggers, it is desirable to have a more flexible and more operationally maintainable RoIB in the future. In this regard, the functionality of the multi-card VMEbus based RoIB is being migrated to a PC based RoIB with a PCI-Express card. Testing has produced a system that achieved the targeted rate of 100 kHz.

This report summarises some of the activities of the HiggsTools initial training network working group in the period 2015–2017. The main goal of this working group was to produce a document discussing various aspects of state-of-the-art Higgs physics at the large hadron collider (LHC) in a pedagogic manner. The first part of the report is devoted to a description of phenomenological searches for new physics (NP) at the LHC. All of the available studies of the couplings of the new resonance discovered in 2012 by the ATLAS and CMS experiments (Aad et al (ATLAS Collaboration) 2012 Phys. Lett. B 716 1–29; Chatrchyan et al (CMS Collaboration) 2012 Phys. Lett. B 716 30–61) conclude that it is compatible with the Higgs boson of the standard model (SM) within present precision. So far the LHC experiments have given no direct evidence for any physical phenomena that cannot be described by the SM. As the experimental measurements become more and more precise, there is a pressing need for a consistent framework in which deviations from the SM predictions can be computed precisely. Such a framework should be applicable to measurements in all sectors of particle physics, not only LHC Higgs measurements but also electroweak precision data, etc. We critically review the use of the κ-framework, fiducial and simplified template cross sections, effective field theories, pseudoobservables and phenomenological Lagrangians. Some of the concepts presented here are well known and were used already at the time of the large electron–positron collider (LEP) experiment. However, after years of theoretical and experimental development, these techniques have been refined, and we describe new tools that have been introduced in order to improve the comparison between theory and experimental data. In the second part of the report, we propose as a new and complementary observable for studying Higgs boson production at large transverse momentum in the case where the Higgs boson decays to two photons. The variable depends on measurements of the angular directions and rapidities of the two Higgs decay products rather than the energies, and exploits the information provided by the calorimeter in the detector. We show that, even without tracking information, the experimental resolution for is better than that of the transverse momentum of the photon pair, particularly at low transverse momentum. We make a detailed study of the phenomenology of the variable, contrasting the behaviour with the Higgs transverse momentum distribution using a variety of theoretical tools including event generators and fixed order perturbative computations. We consider the theoretical uncertainties associated with both and distributions. Unlike the transverse momentum distribution, the distribution is well predicted using the Higgs effective field theory in which the top quark is integrated out—even at large values of —thereby making this a better observable for extracting the parameters of the Higgs interaction. In contrast, the potential of the distribution as a probe of NP is rather limited, since although the overall rate is affected by the presence of additional heavy fields, the shape of the distribution is relatively insensitive to heavy particle thresholds.

The Large Hadron Collider (LHC) at CERN is a proton-proton collider providing the highest energy and the highest instantaneous luminosity ever achieved at a hadron collider. During 2012 runs, bunch crossings occurred every 50 ns. The online event selection system should reduce the event recording rate down to a few hundred Hz in the harsh conditions with many overlapping pp collisions occurring in one bunch crossing. Muons provide a clear signature for many physics processes. They therefore often play an important role in physics analyses such as the recent discovery of a Higgs boson. The ATLAS experiment deploys a three-level online processing scheme. The Level 1 (L1) muon trigger system gets its input from fast muon trigger detectors. Fast sector logic boards select muon candidates, which are passed via an interface board to the central trigger processor and then to the High Level Trigger (HLT). The muon HLT is purely software-based and encompasses a Level 2 (L2) and an Event Filter (EF) trigger for a staged trigger approach. It has access to the data of the precision muon detectors and other detector elements to refine the muon hypothesis. At L2, trigger-specific algorithms are used to increase processing speed by making use of look-up tables and simple algorithms. The EF muon triggers benefit from offline reconstruction software to obtain a precise determination of the track parameters. Algorithms based on two different approaches, namely inside-out and outside-in tracking, are used with a conditional OR to obtain maximal efficiency with minimal processing time. A full overview of the ATLAS muon trigger system is given, the three years of running experience are summarised and a report about online performance such as processing time, trigger rates, efficiency and resolution is given.

In recent years, there was a growing interest in improving the utilization of supercomputers by running applications of experiments at the Large Hadron Collider (LHC) at CERN when idle cores cannot be assigned to traditional HPC jobs. At the same time, the upcoming LHC machine and detector upgrades will produce some 60 times higher data rates and challenge LHC experiments to use so far untapped compute resources. LHC experiment applications are tailored to run on high-throughput computing resources and they have a different anatomy than HPC applications. LHC applications comprise a core framework that allows hundreds of researchers to plug in their specific algorithms. The software stacks easily accumulate to many gigabytes for a single release. New releases are often produced on a daily basis. To facilitate the distribution of these software stacks to world-wide distributed computing resources, LHC experiments use a purpose-built, global, POSIX file system, the CernVM File System. CernVM-FS pre-processes data into content-addressed, digitally signed Merkle trees and it uses web caches and proxies for data distribution. Fuse-mounted files system clients on the compute nodes load and cache on demand only the small fraction of files needed at any given moment. In this paper, we report on problems and lessons learned in the deployment of CernVM-FS on supercomputers such as the supercomputers at NERSC in Berkeley, at LRZ in Munich, and at CSCS in Lugano. We compare CernVM-FS to a shared software area on a traditional HPC storage system and to container-based systems.

TELL1: development of a common readout board for LHCb

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 data acquisition system (DAQ) of the CMS experiment at the CERN Large Hadron Collider assembles events at a rate of 100 kHz, transporting event data at an aggregate throughput of 100 GB/s to the high level trigger (HLT) farm. The HLT farm selects interesting events for storage and offline analysis at a rate of around 1 kHz. The DAQ system has been redesigned during the accelerator shutdown in 2013/14. The motivation is twofold: Firstly, the current compute nodes, networking, and storage infrastructure will have reached the end of their lifetime by the time the LHC restarts. Secondly, in order to handle higher LHC luminosities and event pileup, a number of sub-detectors will be upgraded, increasing the number of readout channels and replacing the off-detector readout electronics with a µTCA implementation. The new DAQ architecture will take advantage of the latest developments in the computing industry. For data concentration, 10/40 Gb/s Ethernet technologies will be used, as well as an implementation of a reduced TCP/IP in FPGA for a reliable transport between custom electronics and commercial computing hardware. A 56 Gb/s Infiniband FDR Clos network has been chosen for the event builder with a throughput of ∼4 Tb/s. The HLT processing is entirely file based. This allows the DAQ and HLT systems to be independent, and to use the HLT software in the same way as for the offline processing. The fully built events are sent to the HLT with 1/10/40 Gb/s Ethernet via network file systems. Hierarchical collection of HLT accepted events and monitoring meta-data are stored into a global file system. This paper presents the requirements, technical choices, and performance of the new system.

In 2017 the LHC reached the record beam luminosity 2 ⋅ 1034 cm−2 s−1, around a factor of two beyond the LHC design value. In December 2018 the Large Hadron Collider (LHC) entered the LS2 phase (Long Shutdown 2), which will last until beginning of 2021, in which the maintainance and upgrade program of LHC and the other smaller accelerators is scheduled. To cope with this and also looking at the following LHC phase in which the luminosity will be increased to 5 ⋅ 1034 cm−2 s−1 the LHC experiments must be upgraded as well. In this context the muon subsystem of the CMS experiment began installing the first GEM based detector station (GE1/1) in July 2019, almost 5 meters from the point of interaction. GE1/1 will consist of 144 triple Gas Electron Multiplier (GEM) detectors, which will work together with the Cathode Strip Chamber (CSC) station ME1/1, improving tracking and triggering of muons produced in the pseudorapidity range of 1.6 < |η| < 2.15. The installation in CMS is now underway at a good pace. The first 72 chambers have been installed together with their services (gas, cooling, low voltage and high voltage etc.) while the completion of the station is foreseen in spring 2020. This contribution will summarize the detector design along with the steps a detector must pass before being approved for the installation in CMS. The status of the operations will be presented, together with the tools developed to monitor the detector parameters during installation. Finally the plans for the installation and commissioning of the entire project will be outlined.

We study the behavior of elastic and diffractive proton dissociation cross sections at high energy. First, we describe what would be expected to be observed at the Large Hadron Collider (LHC) based on conventional Regge theory. We emphasize the tension between these expectations and the recent LHC measurements, and we discuss the possibilty to modify the classic Reggeon Field Theory (RFT) in a physically-motivated way so as to accommodate the tendencies observed at the LHC. As a result, we show that we are able to achieve a "global" description of the wide variety of high energy elastic and diffractive data that are presently available, particularly from the LHC experiments. The model is based on only one pomeron pole, but includes multi-pomeron interactions and, significantly, includes the transverse momentum dependence of intermediate partons as a function of their rapidity, which provides the rapidity dependence of the multi-pomeron vertices. We give predictions for diffractive observables at LHC, and higher, energies.

At the design luminosity, the Large Hadron Collider will have a bunch crossing (BC) rate of 40 MHz with up to 25 pp interactions per BC. For the ATLAS detector, to reduce this large interaction rate to the 200 Hz that can be written offline, a 3-level trigger system is employed. An essential component in achieving this large reduction is the online tracking in the High Level Trigger (HLT), which consists of the Level 2 (L2) and the Event Filter (EF). L2 is the earliest that data from the Inner Detector is available, and uses custom, fast tracking algorithms. The EF uses components from the offline tracking instead. Results are presented for the commisioning and performance of the HLT tracking algorithms in pp collisions from the first few months of the LHC operation and show that the track reconstruction efficiency approaches 100% for tracks with high transverse momentum.