It is hard to determine directly the position of a neutral subatomic particle, but when such a particle decays into a pair of charged particles, it is easy to determine the positions of the charged decay particles and thereby infer the position of the parent particle at the time of its decay. A minimum of two coordinate points for each of the two decay particles is needed to reconstruct the position of the parent vertex. The mathematics of the reconstruction process is inherently interesting, and it can be used to demonstrate to students the utility of some of the most fundamental ideas of vector analysis.
Braithwaite, Edwin S. and Braithwaite, Wilfred J.
"Coplanarity Test for Selecting a Pair of Charged-Particle Tracks Resulting from a Single Neutral-Particle Decay,"
Journal of the Arkansas Academy of Science: Vol. 51
, Article 7.
Available at: http://scholarworks.uark.edu/jaas/vol51/iss1/7