Muon Trigger Research Articles

Operational Experience With the GEM Detector Assembly Lines for the CMS Forward Muon Upgrade

The CMS Collaboration has been developing large-area triple-gas electron multiplier (GEM) detectors to be installed in the muon Endcap regions of the CMS experiment in 2019 to maintain forward muon trigger and tracking performance at the High-Luminosity upgrade of the Large Hadron Collider (LHC); 10 preproduction detectors were built at CERN to commission the first assembly line and the quality controls (QCs). These were installed in the CMS detector in early 2017 and participated in the 2017 LHC run. The collaboration has prepared several additional assembly and QC lines for distributed mass production of 160 GEM detectors at various sites worldwide. In 2017, these additional production sites have optimized construction techniques and QC procedures and validated them against common specifications by constructing additional preproduction detectors. Using the specific experience from one production site as an example, we discuss how the QCs make use of independent hardware and trained personnel to ensure fast and reliable production. Preliminary results on the construction status of CMS GEM detectors are presented with details of the assembly sites involvement.

Participation of JINR in the CDF Experiment

Participation of a Joint Institute for Nuclear Research (JINR) team in the research program at the Tevatron at Fermilab is described. In their work on the upgraded CDF Run II detector, the emphasis was placed on top quark physics. The JINR team was fully engaged in the data analysis of the CDF experiment, particularly, in measuring the top quark mass in the dilepton and lepton–jet modes, in measuring the top quark charge, and in searching for the Higgs boson. The JINR team made a decisive contribution to the operation of the scintillation counter subsystem of the CDF muon trigger, to the trigger based on the vertex silicon detector for selection of events with secondary vertices and to the preshower detector of the electromagnetic calorimeter. The team was involved in the construction, upgrading, and operation of the system of scintillation counters and developed a system for the online monitoring of their parameters to ensure their effective operation in Run II. The work of the JINR researchers was highly appreciated by the international CDF collaboration.

The algorithm of the CMS Level-1 Overlap Muon Track Finder trigger

The CMS Level-1 trigger, based on custom electronics built around FPGA devices, was upgraded in 2016 to achieve the required performance with almost two times higher LHC luminosity than originally designed. The upgraded Level-1 muon trigger merges data from the three muon detectors in the CMS (DT, CSC, and RPC) in the track reconstruction stage — contrary to the legacy trigger which comprised three separate systems each based on one muon detector. This approach allows better use of the detector redundancy and improved measurement of the muon transverse momentum . However, it is particularly challenging in the barrel-endcap transition region, where up to 18 muon chamber layers are present, the detector geometry is complex, and the magnetic field bending the muon tracks is heterogeneous. For this region the Overlap Muon Track Finder (OMTF) uses a novel algorithm based on a naive Bayes classifier. The algorithm identifies the muon tracks and measures their momentum by calculating the probabilities of matching the detector hits to defined transverse momentum hypotheses. The algorithm was tailored to the needs of muon measurements based on the detector data (e.g. to cope with missing hits or multi-muon events) and implementation in FPGA technology. The algorithm details, performance, and optimization methods are discussed in this report. • A novel algorithm was developed for the upgrade of the CMS L1 muon trigger. • It is based on a naive Bayes classifier - a classic machine learning algorithm. • The algorithm performance is significantly better than the legacy muon trigger.

Design and construction of integrated small-diameter drift tube and thin-gap resistive plate chambers for the phase-1 upgrade of the ATLAS muon spectrometer

In the long shutdown for the Phase-1 upgrade of the Large Hadron Collider (LHC) in 2019–2020, 16 new integrated muon tracking and trigger chambers will be installed at the ends of the toroid magnet coils in the small azimuthal sectors of the inner barrel layer (BIS) of the ATLAS muon spectrometer in order to improve the trigger selectivity and fake trigger suppression in the transition region 1 . 0 < | η | < 1 . 3 between the barrel part and the endcaps. The new muon detectors consist of a small-diameter muon drift tube (sMDT) precision tracking chamber with 15 mm tube diameter and a pair of thin-gap RPC chambers with 1 mm gas gap width. The new integrated chamber modules (labeled BIS 78) are currently under construction and will replace the present BIS 7 and 8 MDT tracking chambers with 30 mm diameter drift tubes. The project is the pilot phase for the complete replacement of the small barrel inner layer MDT chambers with the new integrated tracking and trigger detectors in the ATLAS Phase-2 upgrade in 2024–2026 in order to increase the barrel first-level muon trigger coverage and efficiency at the high luminosities at HL-LHC. The sMDT chambers have been chosen to make room for the new trigger chambers and because of their eight times higher rate capability than MDT chambers. The new thin-gap RPC chambers have about 15 times lower avalanche charges and correspondingly increased lifetime and rate capability at HL-LHC and will be operated in coincidence with the endcap trigger chambers. They consist of a triplet of gas gaps which has to be very thin as well and which is supported by a light-weight aluminum structure which is interleaved with the sMDT chamber supports.

The new octal amplifier–shaper–discriminator chip for the ATLAS MDT chambers at HL-LHC

In order to fully exploit the physics potential of the ATLAS experiment at the HL-LHC, the trigger rate of and maximum latency of the first-level trigger system will be increased to 1 MHz and 10 μ s , respectively. In addition, a new first-level muon track trigger with high momentum resolution based on the ATLAS precision Muon Drift-Tube (MDT) chambers will be employed which requires triggerless readout. The TDC ASICs of the current front-end electronics of the MDT chambers are incompatible with these requirements. The front-end boards, each with a TDC chip and three 8-channel amplifier–shaper–discriminator (ASD) chips have to be replaced. Therefore, a new octal ASD2 ASIC has been developed in modern 130 nm IBM/Global Foundries CMOS technology. The chip also contains a Wilkinson ADC to perform both time-over-threshold and signal charge measurement. The ASD design has been fully qualified for the serial production of 80000 chips for ATLAS. The performance in terms of signal rise time and channel uniformity significantly surpasses the one of the previous chip while keeping the power consumption constant. In addition to the characterization with test pulses, several chips have been mounted on the front-end boards and tested in a muon beam at the Gamma Irradiation Facility GIF++ at CERN up to high counting rates where the superior drift time and spatial resolution becomes evident. • New Amplifier–Shaper–Discriminator chips for the readout of ATLAS (s)MDT chambers at HLLHC. • Design of new ASD chip in 130 nm CMOS IBM/Global Foundries technology completed. • Improved signal rise time and channel uniformity. • Radiation hardness far better than needed in the ATLAS muon spectrometer at HLLHC. • Successful full performance test in a muon beam at CERN under intense gamma irradiation.

Performance of the CMS muon system in LHC Run-2

Abstract The CMS muon system has played a key role for many physics results obtained from the LHC Run-1 and Run-2 data. It presently consists of three detector technologies equipping different regions of the spectrometer. Drift Tube chambers (DT) are installed in the CMS muon system barrel, while Cathode Strip Chambers (CSC) cover the CMS end-caps; both serve as tracking and triggering detectors. Moreover, Resistive Plate Chambers (RPC) complement DT and CSC in barrel and end-caps respectively and are mostly used in the trigger. Finally, Gas Electron Multiplier (GEM) chambers are going to be installed in the muon spectrometer endcaps at different stages of the CMS upgrade programme. A slice test consisting of 10 GEM chambers is being presently operated in parallel to the rest of the muon spectrometer. The performance of the different muon detectors and the muon trigger, evaluated using data collected at 13 TeV centre-of-mass energy during the LHC Run2, will be presented in this report in all of its aspects.

Improving of RPC for Muon System of CMS experiment

In the Endcap regions, CMS Muon spectrometer is using Cathode Strip Chambers (CSCs) as muon tracking and trigger detectors, also Resistive Plate Chambers (RPCs) serve as dedicated trigger detectors and improve the muon reconstruction by providing the excellent timing resolution for identification of muon particles. At the present, the four Endcap discs are not fully equipped: RPCs are covering only Endcap disks up to |ŋ| = 1.8. During the Long Shutdown 3 (from 2023 to 2026) of the Large Hadron Collider, Endcap stations 3 and 4 will be further instrumented with new improved RPCs (iRPCs) that will be covering the pseudorapidly region 1.8 < |ŋ| < 2.4, increasing the redundancy in this region. Nowadays, the final design of RPC chambers has been developed and the RPC double gap prototypes with a gas thickness 1.4mm are being tested. The performance and stability of iRPCs at the future HL-LHC upgrades have been studied (detection efficiency, cluster size, rate capability) at the Gamma-Irradiation Facility (GIF++) at CERN, where high energy charged particle beams (mainly muons) are combined with gammas from a 14 TBq 137Cesium source which simulates the background expected at the CMS experiments. In this paper, the main results obtained during the test at GIF ++ are presented.

Flexible trigger menu implementation on the Global Trigger for the CMS Level-1 trigger upgrade

The CMS experiment at the Large Hadron Collider (LHC) has continued to explore physics at the high-energy frontier in 2016. The integrated luminosity delivered by the LHC in 2016 was 41 fb−1 with a peak luminosity of 1.5 × 1034 cm−2s−1 and peak mean pile-up of about 50, all exceeding the initial estimations for 2016. The CMS experiment has upgraded its hardware-based Level-1 trigger system to maintain its performance for new physics searches and precision measurements at high luminosities. The Global Trigger is the final step of the CMS Level-1 trigger and implements a trigger menu, a set of selection requirements applied to the final list of objects from calorimeter and muon triggers, for reducing the 40 MHz collision rate to 100 kHz. The Global Trigger has been upgraded with state-of-the-art FPGA processors on Advanced Mezzanine Cards with optical links running at 10 GHz in a MicroTCA crate. The powerful processing resources of the upgraded system enable implementation of more algorithms at a time than previously possible, allowing CMS to be more flexible in how it handles the available trigger bandwidth. Algorithms for a trigger menu, including topological requirements on multi-objects, can be realised in the Global Trigger using the newly developed trigger menu specification grammar. Analysis-like trigger algorithms can be represented in an intuitive manner and the algorithms are translated to corresponding VHDL code blocks to build a firmware. The grammar can be extended in future as the needs arise. The experience of implementing trigger menus on the upgraded Global Trigger system will be presented.

The ATLAS Level-1 Topological Trigger performance in Run 2

The Level-1 trigger is the first event rate reducing step in the ATLAS detector trigger system, with an output rate of up to 100 kHz and decision latency smaller than 2.5 μs. During the LHC shutdown after Run 1, the Level-1 trigger system was upgraded at hardware, firmware and software levels. In particular, a new electronics sub-system was introduced in the real-time data processing path: the Level-1 Topological trigger system. It consists of a single electronics shelf equipped with two Level-1 Topological processor blades. They receive real-time information from the Level-1 calorimeter and muon triggers, which is processed to measure angles between trigger objects, invariant masses or other kinematic variables. Complementary to other requirements, these measurements are taken into account in the final Level-1 trigger decision. The system was installed and commissioning started in 2015 and continued during 2016. As part of the commissioning, the decisions from individual algorithms were simulated and compared with the hardware response. An overview of the Level-1 Topological trigger system design, commissioning process and impact on several event selections are illustrated.

Muon and B-physics trigger of the ATLAS experiment in Run 2

This paper presents an overview of muon trigger and B-physics trigger of the ATLAS experiment. Main updates done during the preparation for Run 2 data-taking are outlined. Trigger performance results obtained with new experimental data and modelling are shown.

A programmable time alignment scheme for detector signals from the upgraded muon spectrometer at the ATLAS experiment

We present a programmable time alignment scheme used in an ASIC for the ATLAS forward muon trigger development. The scheme utilizes regenerated clocks with programmable phases to compensate for the timing offsets introduced by different detector trace lengths. Each ASIC used in the design has 104 input channels with delay compensation circuitry providing steps of ∼3 ns and a full range of 25 ns for each channel. Detailed implementation of the scheme including majority logic to suppress single-event effects is presented. The scheme is flexible and fully synthesizable. The approach is adaptable to other applications with similar phase shifting requirements. In addition, the design is resource efficient and is suitable for cost-effective digital implementation with a large number of channels.

The New Global Muon Trigger of the CMS Experiment

For the 2016 physics data runs, the L1 trigger system of the compact muon solenoid (CMS) experiment underwent a major upgrade to cope with the increasing instantaneous luminosity of the CERN LHC whilst maintaining a high event selection efficiency for the CMS physics program. Most subsystem specific trigger processor boards were replaced with powerful general purpose processor boards, conforming to the MicroTCA standard, whose tasks are performed by firmware on an field-programmable gate array of the Xilinx Virtex 7 family. Furthermore, the muon trigger system moved from a subsystem centered approach, where each of the three muon detector systems provides muon candidates to the global muon trigger (GMT), to a region-based system, where muon track finders (TFs) combine information from the subsystems to generate muon candidates in three detector regions that are then sent to the upgraded GMT. The upgraded GMT receives up to 108 muons from the processors of the muon TFs in the barrel, overlap, and endcap detector regions. The muons are sorted in two steps and duplicates are identified for removal. The first step treats muons from different processors of a TF in one detector region. Muons from TFs in different detector regions are compared in the second step. An isolation variable is calculated, using energy sums from the calorimeter trigger and added to each of the best eight muons before they are sent to the upgraded global trigger (GT) where the final trigger decision is made. The upgraded GMT algorithm is implemented on a general purpose processor board that uses optical links at 10 Gb/s to receive the input data from the muon TFs and the calorimeter energy sums, and to send the selected muon candidates to the upgraded GT.

Latency study of the High Performance Time to Digital Converter for the ATLAS Muon Spectrometer trigger upgrade

The High Performance Time to Digital Converter (HPTDC), a multi-channel ASIC designed by the CERN Microelectronics group, has been proposed for the digitization of the thin-Resistive Plate Chambers (tRPC) in the ATLAS Muon Spectrometer Phase-1 upgrade project. These chambers, to be staged for higher luminosity LHC operation, will increase trigger acceptance and reduce or eliminate the fake muon trigger rates in the barrel-endcap transition region, corresponding to pseudo-rapidity range 1<|η|<1.3. Low level trigger candidates must be flagged within a maximum latency of 1075 ns, thus imposing stringent signal processing time performance requirements on the readout system in general, and on the digitization electronics in particular. This paper investigates the HPTDC signal latency performance based on a specially designed evaluation board coupled with an external FPGA evaluation board, when operated in triggerless mode, and under hit rate conditions expected in Phase-I. This hardware based study confirms previous simulations and demonstrates that the HPTDC in triggerless operation satisfies the digitization timing requirements in both leading edge and pair modes.

Status and future prospects of the Muon Drift Tubes System of CMS

A key component of the CMS (Compact Muon Solenoid) experiment is its muon system. The tracking and triggering of muons in the central part relies on Drift Tube (DT) chambers. In 2013 and 2014 a number of improvements and upgrades were implemented, in particular concerning the readout and trigger electronics. The increase of luminosity expected by LHC will impose several constraints for rate reduction while maintaining high efficiency in the CMS Level 1 trigger system. In order to exploit the muon detector redundancy, a new trigger system has been designed. The TwinMux system is the early layer of the muon barrel region that combines the primitives information from different subdetectors: DT, Resistive Plate Chambers (RPC) and Outer Hadron Calorimeter (HO). Regarding the long term operation of the DT system, in order to cope with up to a factor 2 nominal LHC luminosity, several improvements will be implemented. The in-chamber local electronics will be modified to cope with the new rate and radiation environment. This paper will present, along with the main system improvements implemented in the system, the first performance results from data collected at 13 TeV center-of-mass energy during 2016, confirming the satisfactory operation of both DT performance and the TwinMux system. A review of the present status and plans for the DT system upgrades will be also described.

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.

The CMS muon system: status and upgrades for LHC Run-2 and performance of muon reconstruction with 13 TeV data

The CMS muon system has played a key role for many physics results obtained from the LHC Run-1 and Run-2 data. During the Long Shutdown (2013–2014), as well as during the last year-end technical stop (2015–2016), significant consolidation and upgrades have been carried out on the muon detectors and on the L1 muon trigger. The algorithms for muon reconstruction and identification have also been improved for both the High-Level Trigger and the offline reconstruction. Results of the performance of muon detectors, reconstruction and trigger, obtained using data collected at 13 TeV centre-of-mass energy during the 2015 and 2016 LHC runs, will be presented. Comparison of simulation with experimental data will also be discussed where relevant. The system's state of the art performance will be shown, and the improvements foreseen to achieve excellent overall quality of muon reconstruction in CMS, in the conditions expected during the high-luminosity phase of Run-2, will be described.

The Partial Truncated Icosahedron Phoswich Detector Array: A Light Charged Particle Array for Pionic Fusion Measurements

The Partial Truncated Icosahedron (ParTI) phoswich detector array has been designed to detect charged pions and other light charged particles in pionic fusion reactions. The array has been constructed and characterized in a series of beam experiments. It is composed of 15 plastic/thalium-doped cesium iodide (CsI(Tl)) phoswich detector units arranged on the faces of a truncated icosahedron geometry which covers approximately 20% of the solid angle. The phoswich detectors have been shown to be capable of isotopic identification of Z = 1 and Z = 2 particles and elemental identification of at least up to Z = 3 using fast vs. slow pulse shape discrimination (PSD). Some advantages of employing digital electronics are discussed including identification of charged pions independent of PSD using their characteristic waveform response and selective event triggering using a muon decay trigger. A calibration method for the array is also described.

The CMS Barrel Muon trigger upgrade

The increase of luminosity expected by LHC during Phase1 will impose tighter constraints for rate reduction in order to maintain high efficiency in the CMS Level1 trigger system. The TwinMux system is the early layer of the muon barrel region that concentrates the information from different subdetectors: Drift Tubes, Resistive Plate Chambers and Outer Hadron Calorimeter. It arranges the slow optical trigger links from the detector chambers into faster links (10 Gbps) that are sent in multiple copies to the track finders. Results from collision runs, that confirm the satisfactory operation of the trigger system up to the output of the barrel track finder, will be shown.

The Level-1 Tile-Muon Trigger in the Tile Calorimeter upgrade program

The Tile Calorimeter (TileCal) is the central hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider (LHC). TileCal provides highly-segmented energy measurements for incident particles. Information from TileCal's outermost radial layer can assist in muon tagging in the Level-1 Muon Trigger by rejecting fake muon triggers due to slow charged particles (typically protons) without degrading the efficiency of the trigger. The main activity of the Tile-Muon Trigger in the ATLAS Phase-0 upgrade program was to install and to activate the TileCal signal processor module for providing trigger inputs to the Level-1 Muon Trigger. This report describes the Tile-Muon Trigger, focusing on the new detector electronics such as the Tile Muon Digitizer Board (TMDB) that receives, digitizes and then provides the signal from eight TileCal modules to three Level-1 muon endcap Sector-Logic Boards.

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.