13 Pattern Recognition and Reconstruction
599
After ambiguity solving, the remaining track candidates are extended into the TRT.
Outside-in tracking first finds track segments in the TRT, using a Hough transform
of the straw centers. A Kalman filter/smoother using also the drift times builds the
final track segments. These track segments are then extrapolated back into the SCT
and the Pixel Detector. Muons are reconstructed in the ID like any other charged
particles; for the standalone reconstruction of muons in the muon system and the
combined reconstruction, see [148].
Based on the experience gained in Run 1, several improvements to track reconstruction were made for Run 2 [149]. For example, the tracking was adapted to the
new insertable B-layer (IBL) [150], and track reconstruction in dense environments
(TIDE) was optimized [151]. This included an artificial neural network based
approach to identify pixel clusters created by multiple charged particles. The effect
of these two developments is shown in Fig. 13.5. In Fig. 13.5a the transverse impact
parameter as a function of track momentum resolution is shown for data taken in
2015 at 13 TeV with the inclusion of the IBL information and for data in 2012 at
8 TeV without the IBL. The data in 2015 was collected with a minimum bias trigger.
The data in 2012 is derived from a mixture of jet, tau and missing E T triggers [150].
Figure 13.5b shows the improvement of the track reconstruction efficiency in the jet
core due to the TIDE optimization [151].
ATLAS track reconstruction efficiency as a function of pseudorapidity and
transverse momentum with simulated data at a center-of-mass energy of 13 TeV
is shown in Fig. 13.6 [152].
[GeV]
T
p
m]
μ
) [
0
(d
σ
0
50
100
150
200
250
300
350
400
ATLAS Preliminary
< 0.2
η
0.0 <
= 8 TeV
s
Data 2012,
= 13 TeV
s
Data 2015,
[GeV]
T
p
-1
10
×
4
1
2
3 4 5 6 7 8910
20
2015/2012
0.6
0.8
1
(a)
R(jet,trk)
Δ
-2
10
-1
10
Track Reconstruction Efficiency
0.7
0.75
0.8
0.85
0.9
0.95
1
ATLAS Preliminary
=13 TeV, Z’(3 TeV)
s
Simulation,
>2 GeV
part
T
<750 GeV, p
jet
T
450
part
decay
<100 mm, R
part
prod
R
TIDE
Light-Jets
B-Jets
Baseline
Light-Jets
B-Jets
(b)
Fig. 13.5 (a) Upper panel: unfolded transverse impact parameter resolution measured from data
in 2015 at 13 TeV with the Inner Detector including the IBL, as a function of track p T for values
of 0.0 < η < 0.2, compared to that measured from data in 2012 at 8 TeV [150]; lower panel: ratio
of the resolution in 2015 over the resolution in 2012. (b) Improvement of the track reconstruction
efficiency due to the TIDE optimization, as a function of the angular distance of the particle from
the jet axis. The track selection is explained in [151]
599
After ambiguity solving, the remaining track candidates are extended into the TRT.
Outside-in tracking first finds track segments in the TRT, using a Hough transform
of the straw centers. A Kalman filter/smoother using also the drift times builds the
final track segments. These track segments are then extrapolated back into the SCT
and the Pixel Detector. Muons are reconstructed in the ID like any other charged
particles; for the standalone reconstruction of muons in the muon system and the
combined reconstruction, see [148].
Based on the experience gained in Run 1, several improvements to track reconstruction were made for Run 2 [149]. For example, the tracking was adapted to the
new insertable B-layer (IBL) [150], and track reconstruction in dense environments
(TIDE) was optimized [151]. This included an artificial neural network based
approach to identify pixel clusters created by multiple charged particles. The effect
of these two developments is shown in Fig. 13.5. In Fig. 13.5a the transverse impact
parameter as a function of track momentum resolution is shown for data taken in
2015 at 13 TeV with the inclusion of the IBL information and for data in 2012 at
8 TeV without the IBL. The data in 2015 was collected with a minimum bias trigger.
The data in 2012 is derived from a mixture of jet, tau and missing E T triggers [150].
Figure 13.5b shows the improvement of the track reconstruction efficiency in the jet
core due to the TIDE optimization [151].
ATLAS track reconstruction efficiency as a function of pseudorapidity and
transverse momentum with simulated data at a center-of-mass energy of 13 TeV
is shown in Fig. 13.6 [152].
[GeV]
T
p
m]
μ
) [
0
(d
σ
0
50
100
150
200
250
300
350
400
ATLAS Preliminary
< 0.2
η
0.0 <
= 8 TeV
s
Data 2012,
= 13 TeV
s
Data 2015,
[GeV]
T
p
-1
10
×
4
1
2
3 4 5 6 7 8910
20
2015/2012
0.6
0.8
1
(a)
R(jet,trk)
Δ
-2
10
-1
10
Track Reconstruction Efficiency
0.7
0.75
0.8
0.85
0.9
0.95
1
ATLAS Preliminary
=13 TeV, Z’(3 TeV)
s
Simulation,
>2 GeV
part
T
<750 GeV, p
jet
T
450
part
decay
<100 mm, R
part
prod
R
TIDE
Light-Jets
B-Jets
Baseline
Light-Jets
B-Jets
(b)
Fig. 13.5 (a) Upper panel: unfolded transverse impact parameter resolution measured from data
in 2015 at 13 TeV with the Inner Detector including the IBL, as a function of track p T for values
of 0.0 < η < 0.2, compared to that measured from data in 2012 at 8 TeV [150]; lower panel: ratio
of the resolution in 2015 over the resolution in 2012. (b) Improvement of the track reconstruction
efficiency due to the TIDE optimization, as a function of the angular distance of the particle from
the jet axis. The track selection is explained in [151]