The LHCb Trigger and its Performance in 2011

TL;DR

This paper describes the design and performance of the LHCb trigger system in 2011, which efficiently filters charm and beauty decays from high-rate proton-proton collisions to enable precise flavor physics measurements.

Contribution

It introduces a two-stage trigger system combining hardware and software to select charm and beauty decays, with performance evaluation using data-driven methods.

Findings

Trigger reduces event rate from 11 MHz to 3 kHz

Effective discrimination of charm and beauty decays from background

Trigger performance validated on multiple decay modes

Abstract

This paper presents the design of the LHCb trigger and its performance on data taken at the LHC in 2011. A principal goal of LHCb is to perform flavour physics measurements, and the trigger is designed to distinguish charm and beauty decays from the light quark background. Using a combination of lepton identification and measurements of the particles' transverse momenta the trigger selects particles originating from charm and beauty hadrons, which typically fly a finite distance before decaying. The trigger reduces the roughly 11\,MHz of bunch-bunch crossings that contain at least one inelastic $pp$ interaction to 3\,kHz. This reduction takes place in two stages; the first stage is implemented in hardware and the second stage is a software application that runs on a large computer farm. A data-driven method is used to evaluate the performance of the trigger on several charm and beauty decay modes.