Abstract
The CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy up to 14 TeV. The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz. The unique CMS trigger architecture only employs two trigger levels. The Level-1 trigger is implemented using custom electronics. The High Level Trigger is implemented on a large cluster of commercial processors, the Filter Farm. Trigger menus have been developed for detector calibration and for fulfilment of the CMS physics program, at start-up of LHC operations, as well as for operations with higher luminosities. A complete multipurpose trigger menu developed for an early instantaneous luminosity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">32</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> has been tested in the HLT system under realistic online running conditions. The required computing power needed to process with no dead time a maximum HLT input rate of 50 kHz, as expected at startup, has been measured, using the most recent commercially available processors. The Filter Farm has been equipped with 720 of such processors, providing a computing power by at least a factor of two larger than expected to be needed at startup. Results for the commissioning of the full-scale trigger and data acquisition system with cosmic muon runs are reported. The trigger performance during operations with LHC circulating proton beams, delivered in September 2008, is outlined and first results are shown.
Highlights
The CMS detector [1] is built and in its final commissioning phase [2], preparing to collect data from the proton-proton collisions to be delivered by the Large Hadron Collider (LHC), at a centre-of-mass energy of up to 14 TeV
The CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy up to 14 TeV
The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz
Summary
The CMS detector [1] is built and in its final commissioning phase [2], preparing to collect data from the proton-proton collisions to be delivered by the Large Hadron Collider (LHC), at a centre-of-mass energy of up to 14 TeV. The CMS experiment employs a general-purpose detector with nearly complete solid-angle coverage, which can efficiently and precisely measure electrons, photons, muons, jets (including tau- and b-jets) and missing energy over a wide range of particle energies and event topologies. These characteristics ensure the capability of CMS to cover a broad programme of precise measurements of Standard Model physics and discoveries of new physics phenomena. The CMS trigger and data acquisition system [3, 4] is designed to cope with unprecedented luminosities and interaction rates. After a concise description of the CMS trigger and data acquisition (DAQ) system, we outline the tests performed for the High Level Trigger (HLT) deployment and validation in the online environment, commissioning with cosmic muon data and first operations with LHC circulating beams
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