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/*!
\page DataFormats_TrackReco Package DataFormats/TrackReco
<center>
<small>
<a href=http://cmsdoc.cern.ch/swdev/viewcvs/viewcvs.cgi/CMSSW/DataFormats/TrackReco/?cvsroot=CMSSW>CVS head for this package</a> -
<a href=http://cmsdoc.cern.ch/swdev/viewcvs/viewcvs.cgi/CMSSW/DataFormats/TrackReco/.admin/developers?rev=HEAD&cvsroot=CMSSW&content-type=text/vnd.viewcvs-markup>Administrative privileges</a>
</small>
</center>
\section desc Description
Persistent classes for Track Reco data format.
\subsection interface Public interfaces
- reco::Track: reconstructed Track. Objects of this type are ment to be stored in the AOD.
<br>Contains a reference to an object of type reco::TrackExtra.
- reco::TrackExtra: Track extension. Objects of this type are ment to be stored in the RECO.
\subsection interface_base Auxiliary base classes
- reco::TrackBase: common base class to reco::Track and reco::Muon
- reco::TrackExtraBase: common base class to reco::TrackExtra and reco::MuonExtra.
Contains references to objects of type TrackingRecHit.
\subsection typedefs
- reco::TrackCollection: collection of reco::Track objects
- reco::TrackRef: persistent reference to a reco::Track object
- reco::TrackRefProd: reference to a reco::Track collection
- reco::TrackRefVector: vector of references to reco::Track objects in the same collection
- reco::track_iterator: iterator over a vector of references to reco::Track objects in the same collection
- reco::TrackExtraCollection: collection of reco::TrackExtra objects
- reco::TrackExtraRef: persistent reference to a reco::TrackExtra object
- reco::TrackExtraRefProd: reference to a reco::TrackExtra collection
- reco::TrackExtraRefVector: vector of references to reco::TrackExtra objects in the same collection
- reco::trackExtra_iterator: iterator over a vector of references to reco::TrackExtra objects in the same collection
\section tiers Track object "Tiers"
The complete track information is stored in two different object:
reco::Track and reco::TrackExtra, that are stored in two different
collection, physically written to fine into two
different ROOT branches. This modularity allows the freedom to "drop"
the reco::TrackExtra component, if not needed, and leave only
reco::Track, in order to save disk space. This could be done,
for instance while writing only the AOD component of a RECO collection.
A reco::Track has a reference (edm::Ref) to a reco::TrackExtra object that
allows to access the information in the "extra" tier. Users don't
necessarily have to dereference this persistent reference, since
reco::Track has two sets of methods:
- inherited from the base class reco::TrackBase, that only
access data stored in the reco::Track object
- specific to reco::Track, that return quantities
derived from reco::TrackExtra information, dereferencing
the corresponding reference.
For instance, the following methods
will only access reco::TrackBase data members:
\htmlonly
<pre>
reco::Track trk;
double pt = trk.pt();
double eta = trk.eta();
</pre>
\endhtmlonly
The following instead access data members contained in reco::TrackExtra:
\htmlonly
<pre>
reco::Track trk;
double outerPt = trk.outerPt();
math::XYZPoint p = trk.outerPosition();
</pre>
\endhtmlonly
and are equivalent to:
\htmlonly
<pre>
reco::Track trk;
const reco::TrackExtraRef & trkExtra = trk.extra();
double outerPt = trkExtra.outerPt();
math::XYZPoint p = trkExtra.outerPosition();
</pre>
\endhtmlonly
<br>
<b>Warning:</b> collections of those two data types are potentially stored in different data tiers.
So, if a reco::TrackExtra is not stored on disk dereferencing the reference contained in
reco::Track may result in an exception.
\section parms Track Parametrization
Track helix parametrization follows the perigee model described
in the internal CMS note <a href="https://cmsdoc.cern.ch/documents/03/in/in03_008.pdf">CMS IN-2003/008</a>.
The five parameters are:
\htmlonly
<ul>
<li> <b><i>κ</i>: signed transverse curvature: <i>&kappa = -<font face="Times New Roman, Times">q • B<sub>z</sub>/p<sub>t</sub></font></i>.
<li> <b><i>θ</i></b>: polar angle of the momentum vector.
<li> <b><i>φ<sub>0</sub></i></b>: azimuthal angle of the momentum vector at the PCA to the beam line.
<li> <b><i><font face="Times New Roman, Times">d<sub>0</sub></font></i></b>: signed transverse distance of the PCA. By convention, the
sign is positive if the reference point is at the left of the PCA.
<li> <b><i><font face="Times New Roman, Times">d<sub>z</sub></font></i></b>: longitudinal distance of the PCA.
</ul>
\endhtmlonly
The five parameters are stored internally in a vector whose index
varies from 0 to 4, in the order listed above. The indices are
also defined as the enumerator <tt>index</tt> defined in the
namespace reco::helix:
\htmlonly
<pre>
enum index { i_transverseCurvature = 0 , i_theta, i_phi0, i_d0, i_dz };
</pre>
\endhtmlonly
So, for instance, in order to access specific track parameters a user
can write the following code that requires no explicit numeric index:
\htmlonly
<pre>
using namespace reco::perigee;
reco::TrackRef track = ... ;
double d0 = track->parameter( i_d0 );
double covThetaPhi = track->covariance( i_theta, i_phi0 );
</pre>
\endhtmlonly
\subsection modules Modules
None.
\subsection tests Unit tests and examples
None.
\section status Status and planned development
To be reviewed.
<hr>
Last updated: @DATE@ L. Lista, Th. Speer
*/
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