Q189 · Practice questionComplex familiar6 marks
QUESTION 189 (6 marks)
Particle X has quark content . Particle Y has quark content . The quark charges are and . Antiquarks have opposite charge and baryon number to their corresponding quarks.
a)[2 marks]
Calculate the charge and baryon number of X.
b)[2 marks]
Calculate the charge and baryon number of Y.
c)[2 marks]
Classify X and Y as baryons, mesons or leptons, giving a constituent-based reason for each.
WORKED SOLUTION
6 marksPractice marking scheme
ANSWER
(a) ; . (b) ; . (c) X is a baryon (three quarks); Y is a meson (a quark and an antiquark).
Worked solution
(a) . For three quarks and no antiquarks, .
(b) The anti-strange charge is . Thus and . Neutrality does not make Y elementary.
(c) Baryons are made of three quarks, so X is a baryon. Mesons contain a quark–antiquark pair, so Y is a meson. Neither is a lepton because both have quark constituents.
Equivalent physically justified methods and consistent equivalent units accepted.
Displayed decimals are model answers; accept appropriate significant figures and consistent rounding from stated constants.
Part a: Add the constituent quark charges.
Part a: Calculate baryon number from three quarks.
Part b: Use the reversed antiquark charge to calculate net charge.
Part b: Use cancelling quark and antiquark baryon numbers.
Part c: Classify X with its three-quark reason.
Part c: Classify Y with its quark–antiquark reason.
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