Abstract
During its second run of operation (Run 2), started in 2015, the LHC will deliver a peak instantaneous luminosity that may reach 2 · 1034 cm-2s-1 with an average pileup of about 55, far larger than the design value. Under these conditions, the online event selection is a very challenging task. In CMS, it is realized by a two-level trigger system: the Level-1 (L1) Trigger, implemented in custom-designed electronics, and the High Level Trigger (HLT), a streamlined version of the offine reconstruction software running on a computer farm. In order to face this challenge, the L1 trigger has been through a major upgrade compared to Run 1, whereby all electronic boards of the system have been replaced, allowing more sophisticated algorithms to be run online. Its last stage, the global trigger, is now able to perform complex selections and to compute high-level quantities, like invariant masses. Likewise, the algorithms that run in the HLT have been greatly improved; in particular, new approaches for the online track reconstruction lead to a drastic reduction of the computing time, and to much improved performances. This document will describe the performance of the upgraded trigger system in Run 2.
Highlights
1.1 The CMS triggerThe Compact Muon Solenoid (CMS) is a multi-purpose experiment built at the Large Hadron Collider (LHC)
In CMS, it is realized by a two-level trigger system: the Level-1 (L1) Trigger, implemented in custom-designed electronics, and the High Level Trigger (HLT), a streamlined version of the offline reconstruction software running on a computer farm
It is made of a silicon tracker subdetector, a homogeneous electromagnetic calorimeter, and a hadron calorimeter immersed in a magnetic field of 3.8 T produced by a superconducting solenoid
Summary
The Compact Muon Solenoid (CMS) is a multi-purpose experiment built at the Large Hadron Collider (LHC). It is made of a silicon tracker subdetector, a homogeneous electromagnetic calorimeter, and a hadron calorimeter immersed in a magnetic field of 3.8 T produced by a superconducting solenoid. Proton bunches collide with a rate of 40 MHz, but only about 1 kHz of collisions is registered for data analysis. This limit is mainly determined by the offline computing resources involved in the offline reconstruction. From L1 trigger, the HLT has access to the full detector information
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