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Understanding Hadrons: Decay, Conservation, and Particle Interactions in Physics

This lesson explores the fascinating world of hadrons, the particles that make up protons and neutrons. Hadrons are divided into mesons and baryons, with distinct properties and interactions. We delve into their classifications, understanding decay processes, and conservation laws like charge and baryon number. While mesons have short lifetimes and zero baryon number, baryons such as protons and neutrons are more stable and comprise three quarks. Discover how these particles interact through fundamental forces and the implications of their decays in particle physics.

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Understanding Hadrons: Decay, Conservation, and Particle Interactions in Physics

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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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