A
trajectory represents the orbit followed by a (charged) particle through the experiment. This
trajectory has a validity range which specifies where the results can be reliably
interpreted (i.e. if a trajectory is extrapolated beyond the bounds of the experiment, there is no guarantee that the results, or the quoted covariances are correct).
A trajectory can be represented by a collection of
states, each of which parameterize the
'local' orbit of the (charged) particle. These
states basically represent straight line
segments, including a covariance matrix. To achieve a 'global' representation of the trajectory, a set of states parameterized as
a function of an 'external' parameter is used. Given the geometry of the experiment, this parameter is
choosen to be the position projected onto the nominal beamaxis, i.e. the z coordinate in the canonical
LHCb reference frame
.
At this point, there is no seperate class which represents a
trajectory. For
a discussion on this subject, please go
here.
--
GerhardRaven - 03 Apr 2005