5.7 X'/Z Projection

If one views an event perpendicular to the beam axis, some tracks are curved and some are straight, depending on the azimuthal angle φ VIEW of the viewing direction. Such a projection is of use only if a sufficiently narrow jet is selected, which may even consist of a single track. In this case a jet based Cartesian coordinate system is optimal, which depends on the direction of the jet axis:

In the X'/Z projection a single track has minimum curvature and maximum angle to the Z axis. It lies in the display screen. The track is seen from the orthogonal side as compared to the Y/X projection (see 5.1 Y/X Projection). The jet image is similar to the one in the ρ/Z projection (see 5.4 ρ/Z Projection), which is however not limited to single jets. This projection provides a second intuitively understandable view of the region around the primary vertex orthogonal to that of the Y'/Z projection (see 5.8 Y'/Z Projection). The momentum of tracks may not be estimated form their curvature in this projection.

Due to the maximum angle between jet and Z axis in the X'/Z projection the sub detector sectors lying in the jet direction can be displayed for the barrel and the endcap. This is specially interesting for the MDT tubes. If only one MDT sector is displayed and the viewing direction is perpendicular to the sector angle, the MDT tubes can be represented as small circles.

The X'/Z Projection Menu (see 3.3.2 Projection Menus)