OCR · A-Level · Physics

    Course version: H556 · Version from Sept 2015

    (e) simple quark model of hadrons in terms of up (u), down (d) and strange…

    Full specification wording

    Fundamental particles: (e) simple quark model of hadrons in terms of up (u), down (d) and strange (s) quarks and their respective anti-quarks

    Hadrons are particles that feel the strong interaction, and the simple quark model explains them as composites of quarks.

    Checked against the OCR H556 specification (opens in a new tab) on .

    • Point 5 of 12
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Hadrons are particles that feel the strong interaction, and the simple quark model explains them as composites of quarks. Baryons such as the proton and neutron contain three quarks (qqq), while mesons such as the pion contain a quark and an anti-quark (qq̄). The model uses up (u), down (d) and strange (s) quarks, each with a corresponding anti-quark: anti-up (ū), anti-down (d̄) and anti-strange (s̄). Anti-quarks carry opposite charge, baryon number and strangeness to their quarks. For example, a proton is uud and a neutron is udd; a π⁺ meson is ud̄. Quark composition determines the hadron's charge, baryon number and strangeness, so you can deduce these properties from the quark content alone.

    What earns the marks

    • Hadrons are particles that interact via the strong force and are not fundamental.
    • Baryons are made of three quarks (qqq); mesons are made of a quark and an anti-quark (qq̄).
    • The simple model uses up (u), down (d) and strange (s) quarks.
    • Each quark has a corresponding anti-quark: ū, d̄ and s̄.
    • Anti-quarks have opposite charge, baryon number and strangeness to their quarks.
    • Quark composition determines a hadron's charge, baryon number and strangeness.

    Common mistakes and how to put them right

    • Thinking mesons contain two quarks rather than a quark and an anti-quark.

      Put it right by stating mesons are qq̄.

    • Believing anti-quarks have the same charge as their quarks.

      Put it right by noting anti-quarks have opposite charge.

    • Assuming all hadrons are baryons.

      Put it right by recalling mesons are also hadrons.

    • Forgetting that strangeness is carried by the strange quark and its anti-quark.

      Put it right by tracking s and s̄ in compositions.

    Exam tips

    • Learn the quark content of the proton (uud) and neutron (udd) as anchors for baryon questions.
    • When given a hadron's quark composition, work out charge, baryon number and strangeness systematically.
    • Check whether a particle is a baryon or meson before applying conservation rules.
    • Practise writing anti-quark symbols clearly to avoid losing marks.

    Try the lesson

    The start of the Fundamental particles: (e) simple quark model of hadrons in terms of up (u), down (d) and strange (s) quarks and their respective anti-quarks lesson, made from checked teaching notes for this specification point.

    Listen

    Hadrons are particles that feel the strong interaction, and the simple quark model explains them as composites of quarks. Baryons such as the proton and neutron contain three quarks (qqq), while mesons such as the pion contain a quark and an anti-quark (qq̄). The model uses up (u), down (d) and strange (s) quarks, each with a corresponding anti-quark: anti-up (ū), anti-down (d̄) and anti-strange (s̄). Anti-quarks carry opposite charge, baryon number and strangeness to their quarks. For example, a proton is uud and a neutron is udd; a π⁺ meson is ud̄. Quark composition determines the hadron's charge, baryon number and strangeness, so you can deduce these properties from the quark content alone. A strong answer earns marks for these points. Hadrons are particles that interact via the strong force and are not fundamental. Baryons are made of three quarks (qqq); mesons are made of a quark and an anti-quark (qq̄). The simple model uses up (u), down (d) and strange (s) quarks. Each quark has a corresponding anti-quark: ū, d̄ and s̄. A common slip: Thinking mesons contain two quarks rather than a quark and an anti-quark. Instead, stating mesons are qq̄. Exam tip: Learn the quark content of the proton (uud) and neutron (udd) as anchors for baryon questions.

    See it

    A top-down flowchart. At the top, a node labelled Hadrons branches into two nodes: Baryons and Mesons. Baryons leads to a node reading Three quarks (qqq), which branches into Proton: uud and Neutron: udd. Mesons leads to a node reading Quark and anti-quark (qq̄), which leads to π⁺ meson: ud̄. Separately, a node reading Quarks: u, d, s leads to Anti-quarks: ū, d̄, s̄, which leads to a node reading Opposite charge, baryon number and strangeness.
    It shows hadrons split into baryons (three quarks) and mesons (a quark and an anti-quark), with example compositions and the quarks and anti-quarks of the simple model.

    Key words

    Say what each word means before you turn the card.

    Hadron classification

    Try answering aloud or in your head before turning the card.

    Quark and anti-quark composition

    Try answering aloud or in your head before turning the card.

    Baryon number and strangeness

    Try answering aloud or in your head before turning the card.

    Charge from quark content

    Try answering aloud or in your head before turning the card.

    See every definition
    Hadron classification
    Hadrons are particles that feel the strong interaction and are not fundamental, and the simple quark model explains them as composites of quarks.
    Quark and anti-quark composition
    Baryons contain three quarks (qqq), while mesons contain a quark and an anti-quark (qq̄), using up (u), down (d) and strange (s) quarks and their respective anti-quarks.
    Baryon number and strangeness
    Anti-quarks carry opposite baryon number and strangeness to their quarks, and quark composition determines a hadron's baryon number and strangeness.
    Charge from quark content
    Anti-quarks carry opposite charge to their quarks, and quark composition determines the hadron's charge, so these properties can be deduced from the quark content alone.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top, a node labelled Hadrons branches into two nodes: Baryons and Mesons. Baryons leads to a node reading Three quarks (qqq), which branches into Proton: uud and Neutron: udd. Mesons leads to a node reading Quark and anti-quark (qq̄), which leads to π⁺ meson: ud̄. Separately, a node reading Quarks: u, d, s leads to Anti-quarks: ū, d̄, s̄, which leads to a node reading Opposite charge, baryon number and strangeness.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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