The Mott problem is an iconic challenge to quantum mechanics theory: how can the prediction of spherically symmetric wave function result in linear tracks seen in a cloud chamber.[1]: 119ff The problem was first formulated in 1927 by Albert Einstein and Max Born and solved in 1929 by Nevill Francis Mott.[2] Mott's solution notably only uses the wave equation, not wavefunction collapse, and it is considered the earliest example of what is now called decoherence theory.[3]
(Also reprinted as Sec.I-6 of Quantum Theory and Measurement, J.A. Wheeler. and W.H. Zurek, (1983) Princeton).