[ Activity 1 : The quark fruit machine]

Use the quark fruit machine to answer the following questions:
Exercise 13

(a) Select the Baryon tab.
(i) Why do no baryons have a charge of
– 2e
?
(ii) What are the possible baryon numbers for the baryons?
(iii) How does the strangeness of a baryon relate to the number of strange quarks it contains?

Reveal answer
Hide
(i) To achieve a charge of
– 2e
requires three constituents each of charge
–
2
 
3
 e
and such constituents would be antiquarks, not quarks, so there is no baryon with this charge.
(ii) All have
B = 1.
(iii)
Strangeness =  – 1 × no. of strange quarks.
(b) Select the Antibaryon tab.
(i) Why do no antibaryons have a charge of
 + 2e
?
(ii) What are the possible baryon numbers for the antibaryons?
(iii) What are the possible charm values of an antibaryon?

Reveal answer
Hide
(i) To achieve a charge of
 + 2e
requires three constituents each of charge
 + 
2
 
3
 e
and such constituents would be quarks, not antiquarks, so there is no antibaryon with this charge.
(ii) All have
B =  – 1.
(iii) An antibaryon may have charm values of
0,  – 1,  – 2
or
– 3,
depending on the number of anticharm quarks that it contains.
(c) Select the Meson tab (note that only 2 of the reels will be displayed).
(i) Why do no mesons have charges of
 + 2e
or
– 2e
?
(ii) What are the possible baryon numbers for the mesons?
(iii) What is the strangeness of a meson comprising a strange quark and an antistrange quark?

Reveal answer
Hide
(i) To achieve a charge of
 + 2e
or
– 2e
requires three constituents each of charge
 + 
2
 
3
 e
or three constituents each of charge
–
2
 
3
 e.
This would make the particle either a baryon or an antibaryon and not a meson, so such charges are not possible.
(ii) All have
B = 0.
(iii)
Strangeness = 0.