.. _tracking:

========
Tracking
========

The main goal of the tracking reconstruction is to find and fit tracks using the hit information provided by the main tracking sub-detectors: PXD, :ref:`SVD<svd>`, CDC.
In general, tracking consists in two steps:

#. pattern recognition, or track finding: recognise the hits belonging to a single charged particle

   .. seealso::

      The `Track Finding at Belle II <https://arxiv.org/abs/2003.12466>`_ provides a nice introduction to Belle II tracking and describe the track finding algorithms and their performance on simulated events.

#. track fit: extract the track parameters from a fit to the pattern (collection of hits).

The tracking reconstruction chain is built as a modular system that can be adapted to different background levels and detector performance. We combine stages of pattern recognition and fitting for the different detectors in order to improve efficiency and minimise fakes and clones.

SVD and CDC provide hits for the first steps of the pattern recognition. In order to optimise the performance of the pattern recognition we have different algorithms for the CDC and for the SVD. Hits in the PXD are added to existing tracks to improve the track quality.

.. note::

   Beside the offline reconstruction, the tracking reconstruction is performed also *online* on the High Level Trigger (**HLT**): the two reconstructions are slightly different. Beside the fact that PXD hits are not available on HLT, tracking on HLT is optimized to satisfy the execution time and memory limits with no significant impact on the physics performance.

Use :ref:`add_tracking_reconstruction<tracking_addtrkreconstruction>` to append the tracking reconstruction to your path:

.. autofunction:: tracking.__init__.add_tracking_reconstruction
		  :noindex:
.. toctree::
   :glob:
   :maxdepth: 2

   trackParameterization
   trackFinding/trackFinding
   trackFitting
   specials
   trackRefining
   trackMatching
   eventTimeExtraction
   pxdDataReduction
   calibration
   scripts
   tools

    
More (?)
--------

The tracking package includes the following sub-packages

.. toctree::
   :glob:
   :maxdepth: 3

   datastore
   dbobjects
   dqmUtils
   modules/*
   spacePointCreation
   svdROIFinder
   tests
   validation
   vxdCaTracking
   vxdMomentumEstimation