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Manuscript Title: Relativistic kinematics for three-body final states.
Authors: W.J. Braithwaite
Program title: BODY3
Catalogue identifier: ABOT_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 4(1972)233
Programming language: Fortran.
Computer: IBM 360/91.
Operating system: OS 360.
RAM: 2K words
Word size: 64
Keywords: Nuclear physics, Kinematics, Final-states, Collision, Three-body, Conservation, Relativistic, Symmetry, Nuclear reaction.
Classification: 17.8.

Nature of problem:
Kinematically-complete relativistic reaction kinematics are calculated for 3-body final states using the principle of conservation of momentum-energy for an isolated system. This program takes, as input, the rest-masses of all the particles (except that of the target), the reaction Q-value, the 3-momentum of outgoing particle 1 and the emission direction of outgoing particle 2. The three-body kinematics problem is then reduced to an equivalent 2-body kinematics problem by constructing effective total momentum-energy values for the subsystem of outgoing particles 2 and 3.

Solution method:
The equivalent 2-body kinematics problem is solved using the FORTRAN IV subroutine TWOBOD. The subroutine is particularly convenient to use as it describes the input momenta and the (unnormalized) direction of particle 2 in terms of their rectangular components in any arbitrary oriented cartesian 3-space. Following the output style of a previously written program, the "test program" generates a table of kinematic values by enumerating, in equal step sizes, the kinetic energy of outgoing particle 1. This table gives the laboratory kinetic energy of energy of outgoing particles 2 and 3, the relative energy of each particle pair (E23, E12, E13), and the outgoing direction (theta, phi) of particle 3. Both kinematic branches are included, when applicable.