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Quarks and antiquarks questions
Three quarks, up, down and strange, build every hadron on the specification. Baryons are made of three quarks, mesons of a quark bound to an antiquark, and beta-minus decay is a single down quark changing into an up quark.
19 original questions · 52 marks · the quarks and antiquarks notes · Particles
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State the electric charge of the up quark and of the down quark, as fractions of the elementary charge e.
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Up quark: +2/3 e (1). Down quark: −1/3 e (1).State the quark composition of a proton and of a neutron.
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Proton: up, up, down (uud) (1). Neutron: up, down, down (udd) (1).State the baryon number of a quark and of an antiquark.
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A quark has baryon number +1/3 (1); an antiquark has −1/3 (1).State the strangeness of the strange quark and of the anti-strange quark.
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Strange quark: strangeness −1 (1). Anti-strange quark: strangeness +1 (1).The π− is the antiparticle of the π+ (up, anti-down). State the quark composition of the π− and show that its charge is −1e.
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The π− is a down quark and an anti-up quark (1). Charge = (−1/3) + (−2/3) = −1e (1).State two properties of a quark that take the opposite sign for its antiquark.
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Charge (1); baryon number or strangeness (1). (Any two of the three.)Show, using the quark charges, that a proton (uud) has a charge of +1e.
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Charge = (+2/3) + (+2/3) + (−1/3) (1)
= +3/3 = +1e (1)Show, using the quark charges, that a neutron (udd) has a charge of 0.
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Charge = (+2/3) + (−1/3) + (−1/3) (1)
= 0 (1)A positive pion is made of an up quark and an anti-down quark. Calculate its charge and its baryon number, showing your working.
State the quark composition of an antiproton and show that its charge is −1e.
The Δ++ baryon has charge +2e, baryon number +1 and strangeness 0. Deduce its quark composition, showing your reasoning. Quark charges: up +2/3 e, down −1/3 e.
In beta-minus decay a down quark changes into an up quark, emitting a W− boson. Show that charge is conserved at this vertex.
Explain, in terms of quark content, why kaons have strangeness +1 or −1 but pions always have strangeness 0.
Describe the beta-minus decay of a neutron in terms of its quarks, naming what the changed quark becomes and the particles emitted.
A positive kaon is made of an up quark and an anti-strange quark. The anti-strange quark has charge +1/3 e and strangeness +1. Determine the charge and the strangeness of the K+, showing your working.
Explain why the quark model assigns the neutron the composition udd rather than uud.
A baryon has charge 0 and strangeness −1. Deduce its quark composition, using only up, down and strange quarks. Quark charges: up +2/3 e, down −1/3 e, strange −1/3 e; the strange quark has strangeness −1.
A student claims to have detected a baryon with charge +1 and strangeness +1. Deduce whether such a particle can be built from up, down and strange quarks and their antiquarks. The strange quark has strangeness −1 and baryon number +1/3; an antiquark has baryon number −1/3.
State the maximum possible charge of a baryon built from up, down and strange quarks, and explain your reasoning. Quark charges: up +2/3 e, down −1/3 e, strange −1/3 e.
The same practice on paper: the printable workbook for this topic, questions and a worked answer book.
Practise quarks and antiquarks one question at a time
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