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Particles and Nuclear Structure

Hadrons: baryons, antibaryons and mesons

  • 3 things to know
  • Component 3

Overview

Recall questions on what a hadron is and which force acts on it, the division into baryons and mesons and the quark content of each, baryon number and its values, why the proton is the only stable baryon, and why every meson is unstable.

What you need to know

Answer each one before you reveal it.

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Key term

Why is a quark never observed on its own?

Key term

Why can a hadron never carry a fractional charge?

Key term

What is a hadron?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a hadron?

    Model answer

    A hadron is a composite particle built from quarks and held together by the strong interaction. Protons, neutrons and pions are all hadrons.

  2. 2

    Why is a quark never observed on its own?

    Model answer

    Quarks are always bound into hadrons by the strong interaction, and pulling them apart takes so much energy that new quark–antiquark pairs are created instead. A free quark is therefore never seen.

  3. 3

    What is a baryon?

    Model answer

    A baryon is a hadron built from three quarks. Its baryon number is +1.

  4. 4

    What is an antibaryon?

    Model answer

    An antibaryon is a hadron built from three antiquarks. Its baryon number is −1.

  5. 5

    What is a meson?

    Model answer

    A meson is a hadron built from one quark and one antiquark. Its baryon number is zero.

  6. 6

    Why does a meson have a baryon number of zero?

    Model answer

    Its quark contributes +1/3 and its antiquark contributes −1/3. The two cancel exactly.

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