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Conservation Rules

Conservation Rules. Particle Physics Lesson 10. Can these happen?. Why/Why not?. Hadrons. There are a very large number of particles that are classified as hadrons , which are subdivided into two further classifications, the mesons , and the baryons . 

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Conservation Rules

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  1. Conservation Rules Particle Physics Lesson 10

  2. Can these happen? Why/Why not?

  3. Hadrons • There are a very large number of particles that are classified as hadrons, which are subdivided into two further classifications, the mesons, and the baryons.  • Hadrons interact by the strong, weak, and electromagnetic force.     • They are not fundamental particles but have a structure. • They have non-zero rest masses, about 1 GeV/c2 • They have an associated value of charge, Q,and baryon numberB. • Hadrons with zero baryon number are called mesons; those with baryon number of 1 are called baryons.

  4. Mesons • These particles have a smaller rest mass than the baryons (and a lower rest mass than the tau lepton).  They have: • Zero baryon number. • Short lifetimes. • Antiparticles

  5. Here are a few mesons: • Notice how short the lifetimes are of these mesons.

  6. We should note the following: • Mesons have TWO quantum numbers that must be conserved in interactions.  The charge is denoted by Q, the baryon number by B.  Mesons have a baryon number of 0. • Mesons have a lepton number of 0.  This must be conserved in any interactions with leptons. • Here is a typical decay:

  7. Notice the conservation of charge and baryon number. • Here are some more:

  8. Show that this interaction can proceed:     • π+μ+ + νm

  9. Answer • Charge +1 ----> + 1 + 0  (Charge is conserved) (P)   • Baryon  0 ----> 0 + 0  (Baryon number is conserved) (P)   • Therefore it can proceed

  10. Baryons • These are the heavyweights of particle physics, and include the familiar proton and neutron. • They are made up of three quarks • They have quantum numbers such as charge and baryon number, which must be conserved in interactions.

  11. Let us look at the properties of the baryons:

  12. Typical Decays

  13. The proton is the only stable baryon.  • All the others spontaneously decay, although the neutron within a nucleus is stable, apart from beta decay.  • The decay times are incredibly short, except the isolated neutron which takes about 8 to 10 minutes.  • Baryons decay to protons, either directly (Σ+π+ + π0) or indirectly (W-Λ0 + K, then Λ0π+ + π-).  • Mesons decay to photons or leptons.

  14. Show that this decay is possible: • Λ0π+ +   π-

  15. Answer • Charge 0  +1 + -1 (Charge is conserved) (P)   • Baryon  1  1 + 0 (Baryon number is conserved) (P)   • The interaction is possible.

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