Abstract
The Large Hadron Collider will be upgraded to provide instantaneous luminosity L = 5 × 1034 cm−2s−1, leading to excessive rates from the ATLAS Level-1 trigger. A double buffer front-end architecture for the ATLAS tracker replacement is proposed, that will enable the use of track information in trigger decisions within 20 μs in order to reduce the high trigger rates. Analysis of ATLAS simulations have found that using track information will enable the use of single lepton triggers with transverse momentum thresholds of pT ∼ 25 GeV, which will be of great benefit to the future physics programme of ATLAS.
Highlights
The Large Hadron Collider will be upgraded to provide instantaneous luminosity L = 5 × 1034 cm−2s−1, leading to excessive rates from the ATLAS Level-1 trigger
Data are transmitted at 160 Mb/s from the Hybrid Chip Controller (HCC) along stave links to a gigabit transceiver and on to a Readout Driver (ROD) via a virtual private link
As there are two banks of five ABC130s each linked at 160 Mb/s into the HCC, but only 160 Mb/s output bandwidth, the buffers on the HCCs will fill faster than they drain
Summary
The ATLAS trigger system [2] consists of: a hardware-based Level-1 (L1) trigger that reduces from the bunch-crossing rate of 40 MHz to ∼75 kHz; a software-based Level-2 trigger that examines in detail Regions of Interest defined by Level-1 and further reduces the rate to ∼3 kHz; and the Event Filter that makes the final decision to record the event, with an output rate of ∼300 Hz. The Level-1 system (Figure 1) is implemented in hardware since it must make decisions within a latency of < 2.5 μs This limit is imposed by the length of the on-detector pipeline memories. The coarse data from the calorimeter and muon systems are used to identify objects such as muons, electrons and photons which satisfy programmable pT thresholds. These objects are passed to the Central Trigger Processor which will accept the event if it meets the requirements specified in the trigger menu. These requirements are based solely on the multiplicity of the trigger objects
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