Chapter 13
Pattern Recognition and Reconstruction
R. Frühwirth, E. Brondolin, and A. Strandlie
13.1 Track Reconstruction
13.1.1 Introduction
Track reconstruction is the task of finding and estimating the trajectory of a charged
particle, usually embedded in a static magnetic field to determine its momentum and
charge. It involves pattern recognition algorithms and statistical estimation methods.
Depending on the physics goals, not all charged tracks have to be reconstructed. For
instance, in many cases there is a physically motivated lower limit on the momentum
or transverse momentum of the particles to be found. Other examples are short-range
secondary particles, such as δ-electrons, that normally need not be reconstructed. It
may also be useful to reconstruct electron-positron pairs from photon conversions
in order to check the distribution of material in the detector. Track reconstruction
frequently proceeds in several steps:
1. Pattern recognition or Track finding: Finds the detector signals (hits) that are
generated by the same charged particle.
2. Track fitting: Estimates for each track candidate the track parameters and the
associated covariance matrix.
3. Test of track hypothesis: Tests for each track candidate whether all hits do indeed
belong to the track and identifies outliers.
R. Frühwirth () · E. Brondolin
Institute of High Energy Physics of the Austrian Academy of Sciences, Vienna, Austria
e-mail: Rudolf.Fruehwirth@oeaw.ac.at; erica.brondolin@cern.ch
A. Strandlie
NTNU—Norwegian University of Science and Technology, Gjøvik, Norway
e-mail: are.strandlie@ntnu.no
© The Author(s) 2020
C. W. Fabjan, H. Schopper (eds.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-35318-6_13
555
Pattern Recognition and Reconstruction
R. Frühwirth, E. Brondolin, and A. Strandlie
13.1 Track Reconstruction
13.1.1 Introduction
Track reconstruction is the task of finding and estimating the trajectory of a charged
particle, usually embedded in a static magnetic field to determine its momentum and
charge. It involves pattern recognition algorithms and statistical estimation methods.
Depending on the physics goals, not all charged tracks have to be reconstructed. For
instance, in many cases there is a physically motivated lower limit on the momentum
or transverse momentum of the particles to be found. Other examples are short-range
secondary particles, such as δ-electrons, that normally need not be reconstructed. It
may also be useful to reconstruct electron-positron pairs from photon conversions
in order to check the distribution of material in the detector. Track reconstruction
frequently proceeds in several steps:
1. Pattern recognition or Track finding: Finds the detector signals (hits) that are
generated by the same charged particle.
2. Track fitting: Estimates for each track candidate the track parameters and the
associated covariance matrix.
3. Test of track hypothesis: Tests for each track candidate whether all hits do indeed
belong to the track and identifies outliers.
R. Frühwirth () · E. Brondolin
Institute of High Energy Physics of the Austrian Academy of Sciences, Vienna, Austria
e-mail: Rudolf.Fruehwirth@oeaw.ac.at; erica.brondolin@cern.ch
A. Strandlie
NTNU—Norwegian University of Science and Technology, Gjøvik, Norway
e-mail: are.strandlie@ntnu.no
© The Author(s) 2020
C. W. Fabjan, H. Schopper (eds.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-35318-6_13
555