Abstract

An overview is presented of the ATLAS triggers that use information from the calorimeter system. The identification of high transverse-energy electrons, photons, τ leptons and jets, as well high missing and total transverse energy, was optimised for the high-luminosity and high-pile-up running conditions at LHC in 2011 and 2012. Results are shown that demonstrate the achieved trigger robustness: the selection of possible physics signatures was performed with high efficiency while maintaining the rates within their required limits.

Highlights

  • − Pile-up noise width varies as a function η, e.g., forward calorimeter region (FCAL) regions in η: bin 1 bin 2 bin 3 bin 4

  • − ETmiss trigger thresholds increased several times in 2011 − Raised noise cuts in FCAL region to strongly suppress rate − Have checked this has minimal impact on trigger efficiency − This allowed thresholds to be lowered at L1 → great benefit for physics analysis

  • − Understanding how current rates behave allows us to predict them at different LHC conditions

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Summary

Introduction

− Total ( ET) and Missing (ETmiss) Transverse Energy (ET): TE and XE − XE-Significance: XS ∼ √XE. Change of beam parameters → steady increase of instantaneous luminosity and average number of interactions per bunch crossing (pile-up) → higher event rates → higher load on all trigger levels, rate=luminosity×cross section energy per beam [ TeV]. Lpeak μ bunch crossing (BC) frequency [ MHz] bunch spacing [ ns] number of filled bunches amplitude function [ m] peak luminosity [1033 cm−2 s−1] average number of interactions per BC. Peak Luminosity per Fill [1033 cm-2 s-1] Peak Luminosity per Fill [1033 cm-2 s-1]

LHC Stable Beams
Interactions per Bunch Crossing
No FCAL
ATLAS Trigger Operations
Trigger run offline
Findings
Summary
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