620 Particle Physics and Cosmology Q46.9 The decays of the muon, tau, charged pion, kaons, neutron, lambda, charged sigmas, xis, and omega occur by the weak interaction. All have lifetimes longer than 10 13 − s. Several produce neutrinos; none produce photons. Several violate strangeness conservation. Q46.10 The decays of the neutral pion, eta, and neutral sigma occur by the electromagnetic interaction. These are three of the shortest lifetimes in Table 46.2. All produce photons, which are the quanta of the electromagnetic force. All conserve strangeness. Q46.11 Yes, protons interact via the weak interaction; but the strong interaction predominates. Q46.12 You can think of a conservation law as a superficial regularity which we happen to notice, as a person who does not know the rules of chess might observe that one player’s two bishops are always on squares of opposite colors. Alternatively, you can think of a conservation law as identifying some stuff of which the universe is made. In classical physics one can think of both
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