In a bubble chamber a neutral particle made at a production vertex leaves no track of…
PHYSICS · Multi-part · Fermi University Physics · Particle Physics & Quantum Fields · Particles, interactions and experiment · Particles, interactions and experiment
Particle Physics, Ch The particle zoo and the four interactions
Problem
In a bubble chamber a neutral particle made at a production vertex leaves no track of its own. Some distance downstream, two tracks of opposite charge start from a single point, a V. One is identified as a proton with momentum 900MeV/c, the other as a π− with momentum 250MeV/c, and the angle between the two tracks at the V is 27.4∘. Nothing else leaves the V. Many such events, all with the neutral particle at the same momentum, give a mean distance of 7.98cm between the production vertex and the V. Take mp=938.272MeV/c2 and mπ=139.570MeV/c2.
((a)) Find the mass of the neutral particle.
((b)) Find its momentum, and hence its mean lifetime τ in its own rest frame.
((c)) Use the charges and baryon numbers of the two decay products to decide whether the neutral particle is a meson or a baryon, and identify it from these candidates: neutral kaon (497.6MeV/c2), neutron (939.6MeV/c2), Λ (1115.7MeV/c2). Name the interaction that ends its life.
((d)) A neutral kaon decaying to π+π− lives 8.95×10−11s. Explain why the lifetime found in (b) could not by itself have told you which particle made the V.