A Measurement of the ATLAS Di-Muon Trigger Efficiency in Proton-Proton Collision at $\sqrt{s}=7$ TeV

TL;DR

This paper measures the efficiency of the ATLAS di-muon trigger system in proton-proton collisions at 7 TeV, crucial for B physics studies involving low-$p_{T}$ di-muon events.

Contribution

It presents the first detailed measurement of the ATLAS di-muon trigger efficiency using real collision data at 7 TeV, comparing two trigger approaches.

Findings

High trigger efficiency achieved for low-$p_{T}$ di-muon events.

Comparison of Level-1 and Level-2 trigger performance.

Results support optimized trigger strategies for B physics analyses.

Abstract

The B physics programme of the ATLAS experiment includes measurements of production cross sections, searches for rare B-decay signatures which are sensitive to new physics at the TeV energy scale and studies of CP violation effects in B-events, such as $B_{s}^{0}\rightarrow J/\psi \phi$ and $B_{d}^{0}\rightarrow J/\psi K_{s}^{0}$. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-$p_{T}$ di-muon events, whilst keeping an acceptable trigger rate. ATLAS developed two separate approaches for triggering on di-muon events from resonances such as $J/\psi$ and Upsilon ($\Upsilon$). The first approach is to start from a di-muon trigger selected at Level-1 while the second is based on dedicated Level-2 algorithms. The performance for these triggers has been studied using collision data at $\sqrt{s}=7$ TeV collected in 2011.