Quarks and antiquarks Flashcards – AQA A-level Physics (7408)

What are the electric charges of the up, down and strange quarks?

Up: $+\frac{2}{3}e$; down: $-\frac{1}{3}e$; strange: $-\frac{1}{3}e$.

What is the baryon number of a quark?

$+\frac{1}{3}$

What are the strangeness values of the up, down and strange quarks?

Up: $0$; down: $0$; strange: $-1$.

How do an antiquark’s charge, baryon number and strangeness compare with those of its corresponding quark?

Each has the opposite sign.

How are the charge, baryon number and strangeness of a composite particle determined from its constituent quarks and antiquarks?

Each is the sum of the corresponding values of its constituents.

How do the constituents of a baryon and an antibaryon differ?

A baryon contains three quarks; an antibaryon contains three antiquarks.

What is the quark composition of a proton?

$uud$

What is the quark composition of a neutron?

$udd$

What is the quark composition of an antiproton?

$\bar{u}\bar{u}\bar{d}$

What is the quark composition of an antineutron?

$\bar{u}\bar{d}\bar{d}$

How is a nucleon’s antiparticle formed from its quark composition?

Replace each quark with its corresponding antiquark.

What are the charges of the proton and antiproton?

Proton: $+e$; antiproton: $-e$.

What are the charges of the neutron and antineutron?

Both have zero charge.

What are the baryon numbers of nucleons and antinucleons?

Nucleons: $+1$; antinucleons: $-1$.

What is the strangeness of a proton or neutron?

Zero.

What is the quark composition of a meson?

A quark and an antiquark.

What is the baryon number of a meson?

$0$

What are the quark compositions of the two charged pions?

$\pi^+ = u\bar{d},\qquad \pi^- = d\bar{u}$

What is the quark composition of the neutral pion?

A quantum superposition of $u\bar{u}$ and $d\bar{d}$ states.

What are the quark compositions of the two charged kaons?

$K^+ = u\bar{s},\qquad K^- = s\bar{u}$

What are the quark compositions of the two neutral kaons?

$K^0 = d\bar{s},\qquad \bar{K}^0 = s\bar{d}$

How does a kaon's strangeness depend on whether it contains a strange or an anti-strange quark?

A kaon containing an anti-strange quark has strangeness $+1$; one containing a strange quark has strangeness $-1$.

What is the equation for neutron beta-minus decay?

$n \rightarrow p + e^- + \bar{\nu}_e$

What quark change occurs in neutron beta-minus decay, and through which interaction?

A down quark changes into an up quark through the weak interaction.

What are the quark compositions of a neutron and a proton?

Neutron: $udd$; proton: $uud$.

Name two quantities conserved in neutron beta-minus decay.

Electric charge and baryon number.