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Particles and Nuclear Structure

Quark composition of the proton, neutron and pions

  • 3 things to know
  • Component 3

Overview

Recall questions on the charges of the first-generation quarks, the compositions of the proton and the neutron and the charge arithmetic that confirms them, the compositions of the charged pions, antiparticle compositions, and why no quark is ever found alone.

What you need to know

Answer each one before you reveal it.

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Key term

Give the quark composition of a proton.

Key term

Give the quark composition of a neutron.

Key term

Give the quark composition of an antiproton.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Give the quark composition of a proton.

    Model answer

    A proton is two up quarks and a down quark, written uud. Its charge is +2/3 + 2/3 − 1/3 = +1e.

  2. 2

    Give the quark composition of a neutron.

    Model answer

    A neutron is one up quark and two down quarks, written udd. Its charge is +2/3 − 1/3 − 1/3 = 0.

  3. 3

    Show that the baryon number of a proton is +1.

    Model answer

    Each of the three quarks in uud carries a baryon number of +1/3. Adding +1/3 three times gives +1.

  4. 4

    Give the quark composition of an antiproton.

    Model answer

    An antiproton is ūūd̄, two anti-up quarks with an anti-down quark. Its charge is −2/3 − 2/3 + 1/3 = −1e.

  5. 5

    Give the quark composition of an antineutron.

    Model answer

    An antineutron is ūd̄d̄, one anti-up quark with two anti-down quarks. Its net charge is zero and its baryon number is −1.

  6. 6

    Give the quark composition of the π⁺ meson.

    Model answer

    The π⁺ is ud̄, an up quark with an anti-down quark. Its charge is +2/3 + 1/3 = +1e.

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