A neutral collision event produces a charged particle at a primary interaction point
PHYSICS · Multi-part · Fermi University Physics · Particle Physics & Quantum Fields · Particles, interactions and experiment · Particles, interactions and experiment
Particle Physics, Ch Hadrons: baryons, mesons and their quark content
Problem
A neutral collision event produces a charged particle at a primary interaction point. That particle travels 3.5cm before it decays at a vertex V2 into a π− track and a second, neutral particle, which leaves no track. The gap between V2 and V1 is 6.3cm: the neutral particle crosses it unseen before it decays at a vertex V1 into a proton track and another π− track. Both flight distances are macroscopic, of order centimetres, and no other tracks are seen at either vertex. At V1 the combined energy and the magnitude of the combined momentum of the proton and π− tracks are E1=1498.26MeV and ∣p1∣c=1000.0MeV. At V2 the combined energy and the magnitude of the combined momentum of the intermediate particle (the one decaying at V1) together with the π− track produced at V2 are E2=1719.56MeV and ∣p2∣c=1100.0MeV. The following data list some baryons of baryon number B=1, with their quark content, charge, strangeness and measured mass: Data (particle: content, Q, S, mass in MeV/c2): n: udd, 0, 0, 939.6; Λ: uds, 0, −1, 1115.7; Σ−: dds, −1, −1, 1197.4; Ξ−: dss, −1, −2, 1321.7.
((a)) Using M2c4=E2−∣p∣2c2, reconstruct the mass of the particle that decays at V1. State, with a reason, which interaction is responsible for this decay.
((b)) Read off the total charge and baryon number carried by the proton and π− tracks at V1, and use them together with the reconstructed mass to identify the particle's quark content and strangeness from the table.
((c)) Reconstruct the mass of the particle that decays at V2. Read off the total charge and baryon number carried by its products (the particle identified in part (b), together with the π− track from V2), and identify its quark content and strangeness from the table.