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R. Frühwirth et al.
Track reconstruction uses hits in the VELO, TT and T stations. Depending on
which detectors are crossed, different track types are defined [160, 161]:
• Long tracks traverse the full tracking system. They have hits in both the VELO
and the T stations, and optionally in TT. They are the most important set of tracks
for physics analyses.
• Upstream tracks pass only through the VELO and TT stations. In general their
momentum is too low to traverse the magnet and reach the T stations.
• Downstream tracks pass only through the TT and T stations. They are important
for the reconstruction of long-lived particles that decay outside the VELO
acceptance.
• VELO tracks pass only through the VELO. These tracks are particularly
important in the primary vertex reconstruction.
• T tracks pass only through the T stations. Like the downstream tracks, they are
useful for particle identification in the Ring Imaging Cherenkov detectors.
Reconstruction of long tracks starts in the VELO. There are two complementary
algorithms to add information from the downstream tracking stations to these VELO
tracks. The first one combines the VELO tracks with information from the T
stations. The second one combines the VELO tracks with track segments found
after the magnet in the T stations, using a standalone track finding algorithm. The
candidate tracks found by each algorithm are then combined, removing duplicates,
to form the final set of long tracks used for analysis. Finally, hits in the TT
consistent with the extrapolated trajectories of each track are added to improve their
momentum determination.
Downstream tracks are found starting with T tracks, extrapolating them through
the magnetic field and searching for corresponding hits in the TT. Upstream tracks
are found by extrapolating VELO tracks to the TT where matching hits are then
added in a procedure similar to that used by the downstream tracking. At least three
TT hits are required to be present by these algorithms.
The found tracks are fitted using a Kalman filter, taking into account multiple
scattering and energy loss due to ionisation. The χ 2 -statistic of the fit is used to
determine the quality of the reconstructed track. If two or more tracks have many
hits in common, only the one with most hits is kept.
The track reconstruction efficiency for the 2012 and the 2015 data as a function
of the momentum can be seen in Fig. 13.9 [162]. The results of the two periods are
compatible.
R. Frühwirth et al.
Track reconstruction uses hits in the VELO, TT and T stations. Depending on
which detectors are crossed, different track types are defined [160, 161]:
• Long tracks traverse the full tracking system. They have hits in both the VELO
and the T stations, and optionally in TT. They are the most important set of tracks
for physics analyses.
• Upstream tracks pass only through the VELO and TT stations. In general their
momentum is too low to traverse the magnet and reach the T stations.
• Downstream tracks pass only through the TT and T stations. They are important
for the reconstruction of long-lived particles that decay outside the VELO
acceptance.
• VELO tracks pass only through the VELO. These tracks are particularly
important in the primary vertex reconstruction.
• T tracks pass only through the T stations. Like the downstream tracks, they are
useful for particle identification in the Ring Imaging Cherenkov detectors.
Reconstruction of long tracks starts in the VELO. There are two complementary
algorithms to add information from the downstream tracking stations to these VELO
tracks. The first one combines the VELO tracks with information from the T
stations. The second one combines the VELO tracks with track segments found
after the magnet in the T stations, using a standalone track finding algorithm. The
candidate tracks found by each algorithm are then combined, removing duplicates,
to form the final set of long tracks used for analysis. Finally, hits in the TT
consistent with the extrapolated trajectories of each track are added to improve their
momentum determination.
Downstream tracks are found starting with T tracks, extrapolating them through
the magnetic field and searching for corresponding hits in the TT. Upstream tracks
are found by extrapolating VELO tracks to the TT where matching hits are then
added in a procedure similar to that used by the downstream tracking. At least three
TT hits are required to be present by these algorithms.
The found tracks are fitted using a Kalman filter, taking into account multiple
scattering and energy loss due to ionisation. The χ 2 -statistic of the fit is used to
determine the quality of the reconstructed track. If two or more tracks have many
hits in common, only the one with most hits is kept.
The track reconstruction efficiency for the 2012 and the 2015 data as a function
of the momentum can be seen in Fig. 13.9 [162]. The results of the two periods are
compatible.