Pseudo-Rapidity, Azimuthal Angle, and Transverse Momentum

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Pseudo-Rapidity Transverse Plane
In CDF the positive z-axis lies along the incident proton beam direction, phi is the azimuthal angle, theta-cm is the polar angle, and PT is the component of momentum in the transverse plane. The pseudo-rapidity, eta, is minus the natural log of the tangent of one-half of the center-of-mass scattering angle, theta-cm.
Eta-phi Space Eta-phi space corresponds to a rectangular coordinate system in which eta is plotted on one axis and phi is plotted on the other. The direction of an outgoing particle is represented by a point in eta-phi space. Particles travelling in the same direction lie near each other in eta-phi space (i.e. small distance d).