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Fundamental Particles

Conservation laws

  • 3 things to know
  • Unit A2 2

Overview

Recall questions on conserving charge, lepton number and baryon number, the values assigned to a baryon, an antibaryon, a lepton and an antilepton, the baryon number of a single quark, checking all three for the decay of a neutron, why an antineutrino accompanies an electron, and using the rules to test whether a proposed interaction is allowed.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

Name the three quantities that must be conserved in every particle interaction

Key term

State the rule for conservation of charge.

Key term

What baryon number is assigned to a baryon, to an antibaryon and to any other particle?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Name the three quantities that must be conserved in every particle interaction at this level.

    Model answer

    Charge, lepton number and baryon number.

  2. 2

    State the rule for conservation of charge.

    Model answer

    The total charge before an interaction must equal the total charge after it.

  3. 3

    What baryon number is assigned to a baryon, to an antibaryon and to any other particle?

    Model answer

    Plus one for a baryon, minus one for an antibaryon, and zero for mesons, leptons and gauge bosons.

  4. 4

    What baryon number does a single quark carry?

    Model answer

    Plus one third, so that three of them give a baryon number of one.

  5. 5

    What lepton number is assigned to a lepton, to an antilepton and to any other particle?

    Model answer

    Plus one for a lepton, minus one for an antilepton, and zero for everything that is not a lepton.

  6. 6

    Why is lepton number conserved separately from baryon number?

    Model answer

    They are independent quantum numbers, and no observed interaction converts a lepton into a baryon or the reverse.

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CBIl becomes B × (q/t) × vt, which is Bqv.

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