V. Büscher

Topological and Central Trigger Processor for 2014 LHC luminosities

The ATLAS experiment is located at the European Center for Nuclear Research (CERN) in Switzerland. It is designed to observe collisions at the Large Hadron Collider (LHC): the worlds largest and highest-energy particle accelerator. Event triggering and Data Acquisition is one of the extraordinary challenges faced by the detectors at the high luminosity LHC collider upgrade. During 2011, the LHC reached instantaneous luminosities of 4 × 1033cm-1s-1 and produced events with up to 24 interactions per colliding proton bunch. This places stringent operational and physical requirements on the ATLAS Trigger in order to reduce the nominal 40MHz collision rate to a manageable event storage rate up to 400Hz and, at the same time, select those events considered interesting. The Level-1 Trigger is the first rate-reducing step in the ATLAS Trigger, with an output rate of 75kHz and decision latency of less than 2.5μs. It is primarily composed of the Calorimeter Trigger, Muon Trigger, the Central Trigger Processor (CTP) and by 2014 a complete new electronics module: the Topological Processor (TP). The TP will make it possible, for the first time, to concentrate detailed information from sub-detectors in a single Level-1 module. This allows the determination of angles between jets and/or leptons, or even more complex observables such as muon isolation or invariant mass. This requires to receive on a single module a total bandwidth of about 1Tb/s and process the data within less than 100 ns. In order to accept this new information from the TP, the CTP will be upgraded to process double the number of trigger inputs and logical combinations of these trigger inputs. These upgrades also address the growing needs of the complete Level-1 trigger system as LHC luminosity increases. During the LHC shutdown in 2013, the TP and the upgraded CTP will be installed. We present the justification for such an upgrade, the proposed upgrade to the CTP, and tests on the TP demonstrator and prototype, emphasizing the characterization of the high speed links and tests of the topological algorithms latency and logic utilization.

A design of scintillator tiles read out by surface-mounted SiPMs for a future hadron calorimeter

Precision calorimetry using highly granular sampling calorimeters is being developed based on the particle flow concept within the CALICE collaboration. One design option of a hadron calorimeter is based on silicon photomultipliers (SiPMs) to detect photons generated in plastic scintillator tiles. Driven by the need of automated mass assembly of around ten million channels stringently required by the high granularity, we developed a design of scintillator tiles directly coupled with surface-mounted SiPMs. A cavity is created in the center of the bottom surface of each tile to provide enough room for the whole SiPM package and to improve collection of the light produced by incident particles penetrating the tile at different positions. The cavity design has been optimized using a GEANT4-based full simulation model to achieve a high response to a Minimum Ionizing Particles (MIP) and also good spatial uniformity. The single-MIP response for scintillator tiles with an optimized cavity design has been measured using cosmic rays, which shows that a SiPM with a sensitive area of only 1 × 1 mm2 (Hamamatsu MPPC S12571-025P) reaches a mean response of more than 23 photon equivalents with a dynamic range of many tens of MIPs. A recent uniformity measurement for the same tile design is performed by scanning the tile area using focused electrons from a 90Sr source, which shows that around 97% (80%) of the tile area is within 90% (95%) response uniformity. This optimized design is well beyond the requirements for a precision hadron calorimeter.

Upgrade of the ATLAS Level-1 Trigger with event topology information

The Large Hadron Collider (LHC) in 2015 will collide proton beams with increased luminosity from 1034 up to 3 × 1034cm−2s−1. ATLAS is an LHC experiment designed to measure decay properties of high energetic particles produced in the protons collisions. The higher luminosity places stringent operational and physical requirements on the ATLAS Trigger in order to reduce the 40MHz collision rate to a manageable event storage rate of 1kHz while at the same time, selecting those events with valuable physics meaning. The Level-1 Trigger is the first rate-reducing step in the ATLAS Trigger, with an output rate of 100kHz and decision latency of less than 2.5µs. It is composed of the Calorimeter Trigger (L1Calo), the Muon Trigger (L1Muon) and the Central Trigger Processor (CTP). By 2015, there will be a new electronics element in the chain: the Topological Processor System (L1Topo system).The L1Topo system consist of a single AdvancedTCA shelf equipped with three L1Topo processor blades. It will make it possible to use detailed information from L1Calo and L1Muon processed in individual state-of-the-art FPGA processors. This allows the determination of angles between jets and/or leptons and calculates kinematic variables based on lists of selected/sorted objects. The system is designed to receive and process up to 6Tb/s of real time data. The paper reports the relevant upgrades of the Level-1 trigger with focus on the topological processor design and commissioning.

Upgrade of the ATLAS Level-1 trigger with an FPGA based Topological Processor

The ATLAS experiment is located at the European Centre for Nuclear Research (CERN) in Switzerland. It is designed to measure decay properties of highly energetic particles produced in the protons collisions at the Large Hadron Collider (LHC). The LHC has a beam collision frequency of 40 MHz, and thus requires a trigger system to efficiently select events, thereby reducing the storage rate to a manageable level of about 400 Hz. Event triggering is therefore one of the extraordinary challenges faced by the ATLAS detector. The Level-1 Trigger is the first rate-reducing step in the ATLAS Trigger, with an output rate of 75 kHz and decision latency of less than 2.5 μs. It is primarily composed of the Calorimeter Trigger, Muon Trigger, the Central Trigger Processor (CTP). Due to the increase in the LHC instantaneous luminosity up to 3×1034 cm-2 s-1 from 2015 onwards, a new element will be included in the Level-1 Trigger scheme: the Topological Processor (L1Topo). The L1Topo receives data in a specialized format from the calorimeters and muon detectors to be processed by specific topological algorithms. Those algorithms sit in high-end FPGAs which perform geometrical cuts, correlations and calculate complex observables such as the invariant mass. The outputs of such topological algorithms are sent to the CTP. Since the Level-1 trigger is a fixed latency pipelined system, the main requirements for the L1Topo are a large input bandwidth (≈1Tb/s), optical connectivity and low processing latency on the real-time data path. This presentation focuses on the design of the L1Topo final production module and the tests results on L1Topo prototypes. Such tests are aimed at characterizing high-speed links (signal integrity, bit error rate, margin analysis and latency) and the logic resource utilization of algorithms.

The Topological Processor for the future ATLAS Level-1 Trigger: From design to commissioning

The ATLAS detector at the Large Hadron Collider (LHC) is designed to measure decay properties of high energetic particles produced in the proton-proton collisions. During its first run, the LHC collided proton bunches at a frequency of 20 MHz, and therefore the detector required a Trigger system to efficiently select events down to a manageable event storage rate of about 400 Hz. By 2015 the LHC instantaneous luminosity will be increased up to 3×1034cm-2s-1: this represents an unprecedented challenge faced by the ATLAS Trigger system. To cope with the higher event rate and efficiently select relevant events from a physics point of view, a new element will be included in the Level-1 Trigger scheme after 2015: the Topological Processor (L1Topo). The L1Topo system, currently developed at CERN, will consist initially of an ATCA crate and two L1Topo modules. A high density opto-electroconverter (AVAGO miniPOD) drives up to 1.6 Tb/s of data from the calorimeter and muon detectors into two high-end FPGA (Virtex7-690), to be processed in about 200 ns. The design has been optimized to guarantee excellent signal integrity of the high-speed links and low latency data transmission on the Real Time Data Path (RTDP). The L1Topo receives data in a standalone protocol from the calorimeters and muon detectors to be processed into several VHDL topological algorithms. Those algorithms perform geometrical cuts, correlations and calculate complex observables such as the invariant mass. The output of such topological cuts is sent to the Central Trigger Processor. This talk focuses on the relevant high-density design characteristic of L1Topo, which allows several hundreds optical links to processed (up to 13 Gb/s each) using ordinary PCB material. Relevant test results performed on the L1Topo prototypes to characterize the high-speed links latency (eye diagram, bit error rate, margin analysis) and the logic resource utilization of the algorithms are discussed.

Comparison of Silicon Photomultiplier Characteristics using Automated Test Setups

Silicon Photomultipliers (SiPM) are photo-sensors consisting of an array of hundreds to thousands pixels with a typical pitch of 10-100 μm. They exhibit an excellent photon counting and time resolution. Therefore applications of SiPMs are emerging in many fields. In order to characterize SiPMs, the PRISMA Detector Lab at Mainz has established three automated test setups. Setup-A is dedicated to measure the gain, the dark count rate and the optical crosstalk probability. The temperature dependencies are characterized by operating the setup in a climate chamber. Setup-B is an optical system to measure the photon detection efficiency. Setup-C addresses the most challenging aspect of comparing SiPMs which is the uniformity of the active surface. Because of the small pixel size, a micro focus lens is attached to a picosecond laser diode to collimate the beam into the sub-structures of the sensors. A three-axis micro-positioning system moves the SiPMs into the focus of the laser spot and then automatically scans the active surfaces. In this paper we present the measurements of several SiPMs and compare their performance.

Status of the DØ Detector

During the data-taking period from 1992 to 1996 (Run I), the Tevatron experiments CDF and DO collected about 125pb¯1 of proton-antiproton collision data at center of mass energies of 1.8 TeV. Since then, the Fermilab accelerator complex has been upgraded to provide collisions at 1.96 TeV and an initial design luminosity of 8.6 × 1031cm¯2s¯1. The new data-taking period (Run II) has started in March 2001 and is expected to deliver more than 10fb¯1 by the year 2007. This dataset is the basis for a rich physics program, including precision mass measurements of the W-boson and top-quark as well as the possibility to discover a light Higgs boson[1].