Figure 20 (left) shows the electron reconstruction efficiency as a function of transverse energyET, measured with tag-and-probe method [27] using 2012 dataset. The efficiency in 2012 is higher than 97%
for ET > 10 GeV and is well reproduced by Monte Carlo simulation within the uncertainty. The right plot of Fig. 20 (right) shows the electron identification efficiencies as a function of ET. ForMedium++
andTight++lepton selections, a 2% level discrepancy is observed. Therefore, the efficiency is corrected in the analysis but the uncertainty associating with the correction is well below 2%, thus negligible.
[GeV]
Cluster ET
20 30 40 50 60 70 80
Reconstruction Efficiency
0.75 0.8 0.85 0.9 0.95 1 1.05
Reconstruction and track quality efficiency L dt = 4.7 fb-1
∫
=7 TeV s 2011 data 2011 MC
L dt = 20.7 fb-1
∫
=8 TeV s 2012 data 2012 MC
ATLAS
Preliminary "η"<2.47
[GeV]
ET
10 20 30 40 50 60 70 80 90 100
Efficiency
0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
L dt = 20.3 fb-1
∫
s = 8 TeV Z→ ee ATLASPreliminary2012
| < 2.47
|η Loose Loose, MC Multilepton Multilepton, MC Medium Medium, MC Tight Tight, MC
Figure 20: (Left) Efficiency of electron reconstruction is shown as a function of transverse energyET
for the electrons in the central part of the detector with|η|<2.47 for data (filled markers) and MC (open markers) for 2011 (triangles) and 2012 (circles) datasets. The total (statistical and systematic) uncertainty is displayed as the error bars. (Right) Identification efficiency of electrons fromZ →eedecay forLoose, Multi-lepton,MediumandTightselections are shown as a function ofETfor|η|<2.47. These plots are cited from Ref. [27].
should be combined to select pure muon tracks.
3.4.3 STACO muons
Match chi-squareχ2match is defined as the difference between the standalone muon track and the inner detector track vectors weighted by their combined covariance matrix:
χ2match =(TMS−TID)T(CMS+CID)−1(TMS−TID). (48) HereTdenotes a vector of track parameters andCis the covariance matrix. The subscript ID refers to the inner detector and MS to the muon spectrometer. The pair having the bestχ2match is chosen for the combination. Then the combined muon track vector is given by
T=+
C−ID1+C−MS1,−1+
C−ID1TID+C−MS1TMS,
. (49)
ID information dominates the measurement up to pT=80 GeV in the barrel and pT=20 GeV in the end-cap. For higher pT(<
∼100 GeV), the ID and MS measurements have similar weight while the MS domi-nates in pT>
∼100 GeV.
3.4.4 Segment-tagged muons
Segment-tagged muon reconstruction starts from Inner Detector tracks, extrapolates them to the inner station of Muon Spectrometer, and tries to match them to the segments not yet associated to the muons reconstructed by STACO algorithm. Segment-tagged muon algorithm provides an efficiency improve-ment for low pTmuons.
3.4.5 Hard muon definition
Both STACO and Segment-tagged muons are combined to increase the reconstruction efficiency over a widepTrange. To improve purity, the following hit qualities are required for the candidate muons.
• The number of hits in the pixel detector should be larger than 1. If, after the reconstruction, the pixel sensor which is passed by the track is found to be malfunctioning, the number of hits is increased by the number of such malfunctioning sensors to increase efficiency.
• Similarly, the number of SCT hits are requested to be greater than 6. Again, the number of mal-functioning SCT sensors are added up to the number.
• If more than 3 holes are found in Pixel and SCT detectors along the extrapolated track, the track quality is judged as bad.
• If the muon passes a working innermost pixel sensor, a hit should be recorded in that sensor.
• If|η| < 1.9, the number of TRT hits should be larger than 5 and the outlier tubes near the track should not exceed more than 10% of the total TRT hits.
• If|η|≥1.9 and the number of TRT hits is larger than 5, the outlier tubes near the track should not exceed more than 10% of the total TRT hits.
To reject fake muons from hadron decays, muons within∆R<0.4 from an overlap removal jet (defined in Section 3.2.7) is vetoed.
Then the following muons are defined:ETmissmuon, loose muon, preselected muon and signal muon.
The usages for these muons are the same as electrons in the previous section. The isolation condition of signal muon is different from that of electron, which is
ptcone20<1.8 GeV, (50)
whereptcone20is the sumpTof all tracks within∆R<0.2. The definitions are summarized in Table 6.
3.4.6 Soft muon definition
Most of the definitions are the same as those of Hard Muon. Here we see only the differences. First, pT thresholds are changed to 6 GeV for all muons. In addition, signal muon is requested to pass the following isolation conditions
• ptcone30<1.2 GeV,
• |zPV0 sinθ|<0.4 mm,
• |dPV0 /σ(d0PV)|≤3.
zPV0 is the track distance from the primary vertex along the beam axis andθis the polar angle of the track.
d0PV is the radial distance between the track and the Primary Vertex. σ(d0PV) is the uncertainty ofd0PV. Table 7 gives the summary of soft muon definition.
3.4.7 Performance
Figures 21 show the muon efficiency as a function of pT(left) andη(right). The muons reconstructed by both STACO and Segment-tagged algorithms are combined. The efficiency is larger than 98% for pT>20 GeV, and the discrepancy between data and Monte Carlo is well below 1%. The discrepancy is corrected by introducing a correction factor, but the impact is negligible.
20 30 40 50 60 70 80 90 100
0.8 0.85 0.9 0.95 1
Data, CB+ST muons MC, CB+ST muons
ATLASPreliminary 2012 Data, Chain 1 L dt = 20.7 fb-1
∫
| < 2.5 0.1 < |η
[GeV]
pT
20 30 40 50 60 70 80 90 100
Data/MC 0.98 1
1.02 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
0.5 0.6 0.7 0.8 0.9 1
Data, CB+ST muons MC, CB+ST muons
ATLASPreliminary 2012 Data, Chain 1 L dt = 20.7 fb-1
∫
> 20 GeV pT
η -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 Data/MC 0.98
1 1.02
Figure 21: Reconstruction efficiency for STACO and Segment-tagged muons as a function of pT(left) and|η|(right). The bottom panel shows the ratio between data and Monte Carlo. These plots are cited from Ref. [30].
Cut Value/description
Muon Type Preselected ETmiss Loose Signal Acceptance pT >10 GeV pT>25 GeV
|η|<2.4 Overlap Removal ∆R(µ,jet)>0.4
Isolation – ptcone20<1.8 GeV
Table 6: Summary of the hard muon selection criteria.
Cut Value/description
Muon Type Preselected EmissT Loose Signal
Acceptance pT >6 GeV
|η|<2.4 Overlap Removal ∆R(µ,jet)>0.4
Isolation – ptcone30<1.2 GeV
Impact Parameter – |zPV0 sinθ|<0.4 mm – |dPV0 /σ(d0PV)|≤3 Table 7: Summary of the soft muon selection criteria.