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Strange Particles AS level Notes

Strange Particles AS level Notes. Strange Particles. By the 1950s, many new particles were being discovered with the use of accelerators (you study those at A2 – they accelerate charged particles by using magnetic and electric fields.)

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Strange Particles AS level Notes

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  1. Strange ParticlesAS level Notes

  2. Strange Particles • By the 1950s, many new particles were being discovered with the use of accelerators (you study those at A2 – they accelerate charged particles by using magnetic and electric fields.) • They were produced from collisions between protons, neutrons, and pions

  3. Strange Particles • Some of these particles were called strange particles because of some strange properties in their production and decay! • They were always produced in pairs • Some would decay and not have a proton or a neutron as an end product • All are unstable • All are created by strong force interactions and often decay via the weak force

  4. Strange Particles • Contain an 's' quark or anti-quark • Have surprisingly long lives (100,000 times longer than expected!) • Are produced in pairs which suggests that they have an additive conserved quality.

  5. Our Syllabus • There are lots of different types of strange particles but • The only one you need to know about for the AQA syllabus at AS level is: the kaon - k

  6. Kaon k • Mass = ½ proton mass • Spin = 0 • Two particles: k+, k0 • Two antiparticles: k-, k0-bar • Lifetime = 10-8 or 10-10 seconds

  7. Kaon k • In 1947 the British physicists Rochester and Butler observed the new kaon particles. • They observed these particles in two matter forms: • a neutral one ko that decayed into the pions p+ and p- , and a • positively charged one that decayed into a muon m+ (a muon is basically like a heavy electron) and a photon.

  8. What is the problems with that? • You cannot make the quarks add up properly! • Strangeness (which looked so ‘conservative’ because of pair production) was not conserved in weak interaction decays

  9. Truly Strange Particles! • Strangeness is not conserved when weak interactions take place – that is how it is possible for the decays of strange particles into none strange ones! • So, if strangeness is not conserved that is evidence of a weak interaction in these particles in the reaction concerned.

  10. Conservation of Strangeness • Strangeness must be conserved in all strong and electromagnetic interactions, but • not conserved in weak interactions

  11. Creation of Strange Particles • Strange particles are always created in pairs by strong processes in such a way that the total strangeness remains zero. • If one particle has strangeness then the other must have strangeness. • An example of strange particle production is when a negative pion collides with proton, giving rise to a neutral lambda particle and a neutral kaon.

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