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PH 103

PH 103. Dr. Cecilia Vogel Lecture 24. From the particle adventure webpage. Review. Particles Antimatter conservation laws Mesons and baryons. Outline. forces: 4 fundamental interactions particles affected force carriers. The Four Fundamental Forces. Gravity Electromagnetic Strong

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PH 103

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  1. PH 103 Dr. Cecilia Vogel Lecture 24 From the particle adventure webpage

  2. Review • Particles • Antimatter • conservation laws • Mesons and baryons Outline • forces: • 4 fundamental interactions • particles affected • force carriers

  3. The Four Fundamental Forces • Gravity • Electromagnetic • Strong • Weak • forces are interactions • What about friction? VanderWaals? etc • These are not fundamental, • just consequences of electromagnetic interaction of electrons in atoms. • What about strong nuclear force? • Just a consequence of the strong force between the quarks in p’s and n’s.

  4. Gravity • What particles feel gravity? • Anything that has mass. Ex: electron, galaxy • Anything that has energy. Ex: photon, n. • Pretty much everything! • Have we seen its effects? • Earth goes around Sun • Apples fall on people’s heads • Not a sizeable force for microscopic objects • Often ignored in atomic, nuclear, and particle physics

  5. Electromagnetic • What particles feel EM force? • Anything that has electric charge (or is made up of charged particles) • Have we seen its effects? • Electrons are held in atoms. • Electrons flow in circuits. • Static-y clothes stick together. • Magnets stick to fridges. • Compasses point North

  6. Strong • What particles feel strong force? • Anything that has color charge • i.e. All quarks • and anything made up of quarks • And gluon… to be introduced later • Have we seen its effects? • Nuclei are held together by it • Quarks are held together by it • held so strongly, they cannot be isolated • Decays: alpha decays occur by strong interaction

  7. Weak • What particles feel weak force? • Anything that has flavor • Flavor = what distinguishes one quark or lepton from another. • i.e. all matter and antimatter • Have we seen its effects? • Does not hold anything together! • too weak! • Decays: beta-plus and beta-minus decays occur by weak interaction

  8. Recall Quarks and Leptons up charm top down strange bottom (electron) neutrino (ne) mu neutrino (nm) tau neutrino (nt) electron (e-) muon (m-) tau (t -) • What forces does each particles feel?

  9. How do Forces Work? • One particle is here, another over there, • how do they interact, how are they aware of each other? • Spooky action-at-a-distance? • No — they “communicate” by exchanging particles.

  10. Virtual Particles • Exchange particles come into existence, • even if particles exchanging them don’t lose energy • If exchange particle has mass, • the mass energy created from nowhere • What??? Energy from nowhere? Isn’t energy conserved??

  11. Virtual Particles • If exchange particle has mass, • the mass energy created from nowhere, but… • HUP allows non-conservation of energy • for a very short period of time

  12. Virtual Particles • If exchange particle has mass, • HUP allows it to exist • for a very short period of time • Where DE = (mass of virtual particle)c2 • Virtual particle can’t go far, so • forces with massive exchange particles are very short range.

  13. Exchange Particles • AKA force-carriers, gauge bosons, field quanta. • Particles exert forces on each other by exchanging these particles. • Force-carriers are not “matter” particles • even though some have mass • Force carriers come and go; • their number is not conserved. • You can create or destroy as many as you want. • (unlike quarks and leptons)

  14. Carriers for Each Force • Electromagnetic • photon • No surprise: Photon is quantum of electromagnetic energy. • Strong • gluon • Weak • W-particles and Z-particles • Gravity • graviton? • are there gravity waves like EM wave? • if there are, are they quantized?

  15. Gauge Bosons There are six different gauge bosons photon g gluon g graviton Z0 W+ W- massless massive • What forces does each particle feel? • NOTE: By “feel” we are excluding the fact that these particles are created and destroyed in exchange.

  16. Fundamental Particles • We now have all the fundamental particles that have been found (plus one that hasn’t). • Matter • 6 quarks • + and - • 6 leptons • charged and neutral • Antimatter • ditto • 6 Gauge Bosons • 3 massless • 3 massive

  17. Search for the Higgs • Recall that the mass of a nucleus is less than the mass of its constituent protons and neutrons. • Also, the mass of a proton is only partly due to constituent quarks. • Interactions contribute to mass. • What if all mass comes from interactions? • interactions with what? • hypothetical Higgs boson!

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