Performance of the ATLAS muon trigger in pp collisions at [Formula: see text] TeV

Abstract

The performance of the ATLAS muon trigger system is evaluated with proton-proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of [Formula: see text] bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum [Formula: see text] GeV, with a statistical uncertainty of less than 0.01 % and a systematic uncertainty of 0.6 %. The [Formula: see text] range for efficiency determination is extended by using muons from decays of [Formula: see text] mesons, [Formula: see text] bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.

Fig. 1

A schematic picture showing a quarter-section of the muon system in a plane containing the beam axis, with monitored drift tube (MDT) and cathode strip (CSC) chambers for momentum determination and resistive plate (RPC) and thin gap (TGC) chambers for triggering

Fig. 2

Trigger rates as a function of instantaneous luminosity a for selected muon triggers at Level-1 and b for selected single- and multi-muon triggers at the event-filter as denoted in the legend (see Table 1 for details)

Fig. 3

Trigger rate of the Level-1 MU15 as a function of a pseudorapidity ${\mathit{\eta }}_{{\mathrm{L}}_1}$ of all the trigger objects (light histogram) and of the ones associated with offline reconstructed muons (dark histogram) and b instantaneous luminosity, for all triggers (dots) and for the fake ones not-associated with offline-reconstructed muons (triangles) with the lines representing the results of the corresponding linear fits

Fig. 4

Rate of the isolated single-muon trigger, mu24i, at the event-filter a as a function of pseudorapidity ${\mathit{\eta }}_{\mathrm{EF}}$ for all combined-muons (light histogram) and for the ones associated with offline reconstructed muons (dark histogram), b as a function of the transverse momentum $p_{\mathrm{T}}$ threshold at the event-filter (EF) at an instantaneous luminosity of $7\times {10}^{33}$ cm${}^{-2}$ s${}^{-1}$, for combined-muons in the data (dots) compared to the expectations from $W$- and $Z$-bosons production and from the data-driven estimate for multi-jet production, as described in the legend

Fig. 5

Resolution difference in transverse momentum $p_{\mathrm{T}}$ determination in the offline and in the event-filter reconstruction, as a function of $p_{\mathrm{T}}$ of the offline muon

Fig. 6

Resolution difference in the a pseudorapidity $\mathit{\eta }$ and b  azimuthal angle $\mathit{\varphi }$ determination in the offline and in the event-filter reconstruction, as a function of $p_{\mathrm{T}}$ of the offline muon

Fig. 7

Efficiency to pass either mu24i or mu36 triggers, as a function of the number of reconstructed vertices in an event, N${}_{\mathrm{vtx}}$ in a the barrel region, and in b the endcap region, for data (dots) and MC simulation (bands). The lower panels show the ratio of the efficiencies in data and in MC simulation. The error bars reflect statistical uncertainties only

Fig. 8

Efficiency of passing either the mu24i or mu36 trigger as a function of the probe-muon transverse momentum $p_{\mathrm{T}}$, for a the barrel region and b the endcap region, for data (dots) and MC simulation (bands). The lower panels show the ratio of the data and MC efficiencies. The error bars include both statistical and systematic uncertainties

Fig. 9

Efficiency of passing either the mu24i or mu36 trigger as functions of the probe-muon transverse momentum $p_{\mathrm{T}}$, for the three trigger levels, Level-1, Level-2 and event-filter, in the data for a the barrel region and b the endcap region. The error bars show the statistical uncertainties only

Fig. 10

Ratio of the data and MC efficiencies to pass either the mu24i or the mu36 trigger, in bins of the probe-muon $\mathit{\eta }$ and $\mathit{\varphi }$ in a the barrel region and b the endcap region

Fig. 11

Efficiency of single-muon triggers, mu13, mu18, mu24i, mu36 and mu40_SA_barrel, measured in data as a function of the probe-muon transverse momentum $p_{\mathrm{T}}$, for a the barrel region and b the endcap region. The error bars indicate statistical uncertainties only

Fig. 12

Efficiency of the mu8_FS trigger measured as a function of the reconstructed number of vertices in an event, N${}_{\mathrm{vtx}}$ in a the barrel region and b the endcap region, in the data (dots) and in the MC simulation (bands) The lower panels show the ratio of efficiencies of data and MC simulation. The error bars represent statistical uncertainties only

Fig. 13

Efficiency of the event-filter full-scan mu8_FS as a function of the probe-muon transverse momentum $p_{\mathrm{T}}$, separately in a the barrel region and b the endcap region

Fig. 14

Ratio of the data and MC efficiencies for the mu8_FS trigger in bins of the probe-muon pseudorapidity $\mathit{\eta }$ and azimuthal angle $\mathit{\varphi }$, in a the barrel region and b the endcap region

Fig. 15

Efficiency of low transverse momentum $p_{\mathrm{T}}$ single-muon triggers, mu4, mu6 and mu8, as a function of the probe-muon transverse momentum $p_{\mathrm{T}}$ in a the barrel region and b the endcap region, in the data (symbols) and in the MC (bands). The error bars for MC indicate the statistical uncertainties only, while those for data indicate both the statistical and systematic uncertainties

Fig. 16

Ratio of the data and MC efficiencies of the mu4 trigger in bins of the probe-muon pseudorapidity $\mathit{\eta }$ multiplied by its charge, $Q\mathit{\eta }$, and the transverse momentum $p_{\mathrm{T}}$

Fig. 17

Efficiency of the mu24i trigger as a function of the probe-muon transverse momentum $p_{\mathrm{T}}$, as measured with the top quark and $W$ $+$ jet candidate events in the a barrel and b endcap regions. The lower panels show the ratio of the efficiencies in the data and MC simulation. Also shown is the efficiency as measured with the $Z$ decays using the tag-and-probe method. The error bars for MC simulation indicate the statistical uncertainties only while the error bars for data include both statistical and systematic uncertainties