Fundamental particles

What is not a quark flavour?

A. Charm.

B. Meson.

C. Strange.

D. Up.

Answer: B

In the quark model, the hadrons are made up of fundamental particles called quarks. Three types of quark, called flavours of quark, were initially introduced: up (u), down (d) and strange (s). The total number of types of quark or ‘flavours’ is considered to be six. The additional flavours are charm (c), bottom (b) and top (t)

Thus, the six quark flavours are:

up (u)

down (d)

strange (s)

charm (c)

bottom (b)

top (t)

How many down quarks are in a nucleus of hydrogen-3, ₁³H ?

A. 2.

B. 3.

C. 4.

D. 5.

Answer: D

1 proton → quark composition = uud → 1 down quark.

2 neutrons → each neutron = udd → Total from 2 neutrons = $4$ down quarks.

Which fundamental particles form a hadron?

A. Leptons.

B. Nucleons.

C. Photons.

D. Quarks.

Answer: D

Hadrons are particles that are affected by the strong nuclear force and are made up of quarks.

There are two types of hadrons:

Baryons are made of 3 quarks.

Mesons are made of 1 quark + 1 antiquark.

A particle Q and a particle R are each composed of one quark and one antiquark.

a. State the name of the class (group) of particles that includes Q and R.

b. Q has a charge of −1e, where e is the elementary charge. R has a charge of 0.

Complete table to show a possible second quark in each of Q and R. 

a. Mesons (or Hadrons).

b. Q: anti-up, anti-charm, or anti-top.R: up, charm, or top.

What is the charge, in terms of the elementary charge $e$, on a charm quark?

A. `-2/3e`

B. `-1/3e`

C. `+1/3e`

D. `+2/3e`

Answer: D

Which combination of up (u) and down (d) quarks forms a neutron?

A. u u u

B. u u d

C. u d d

D. d d d

Answer: C

A neutron is composed of one up quark (u) and two down quarks (d).

Each quark has a specific electric charge: up quark `+2/3e`, down quark `-1/3e`

So for u d d: `"Charge" = (2/3)e - (1/3)e - (1/3)e = 0e`

A `pi^+` meson has a charge of +e, where $e$ is the elementary charge. It consists of an up quark and one other quark.

What could be the other quark in the `pi^+` meson?

A. Anti-down.

B. Anti-up.

C. Bottom.

D. Charm.

Answer: A

Mesons are hadrons made up of one quark and one antiquark. The `pi^+` meson is made of an up quark and an anti-down quark.

Known charges: up `+2/3e`, anti-down `+1/3e` 

Hence, total charge: +1e.

A stationary nucleus has nucleon number A.

The nucleus decays by emitting a proton with speed v to form a new nucleus with speed u. The new nucleus and the proton move away from one another in opposite directions.

Which equation gives v in terms of A and u?

A. `v=(A/4-1)u`

B. `v=(A-1)u`

C. `v=Au`

D. `v=(A+1)u`

Answer: B

Because they move in opposite directions, their momenta are equal and opposite:

Momentum of proton = momentum of daughter nucleus.

`1xxv=(A−1)xxu`

`v=(A−1)xxu`

What is a general description of a baryon?

A. It consists of three quarks that must all be the same flavour.

B. It consists of three quarks that do not need to be the same flavour.

C. It consists of two quarks that must both be the same flavour.

D. It consists of two quarks that do not need to be the same flavour.

Answer: B

A. Incorrect: Proton is uud.

B. Correct: 

Baryons are hadrons made up of three quarks. They can be of different flavours - for example:

Proton = uud; Neutron = udd.

So baryons consist of 3 quarks, and these quarks can be different in flavour.

C. Incorrect: a particle with 2 quarks - this refers to mesons, not baryons.

D. Incorrect: a particle with 2 quarks - this refers to mesons, not baryons. 

a. Nucleus P and nucleus Q are isotopes of the same element.

Nucleus Q is unstable and emits a β⁻ particle to form nucleus R.

i. For nuclei P and Q, compare:

The number of protons.

The number of neutrons.

ii. When nucleus Q decays to form nucleus R, the quark composition of a nucleon changes.

State the change to the quark composition of the nucleon.

iii. State the name of another particle that must be emitted from nucleus Q in addition to the β⁻ particle.

b. A hadron consists of two charm quarks and one bottom quark.

Determine, in terms of the elementary charge e, the charge of the hadron.

a.

i. Number of protons: equal/same.

Number of neutrons: unequal/different.

ii. In β⁻ decay, a down quark changes to an up quark, emitting an electron and antineutrino.

So, change: down → up.

iii. In β⁻ decay, an electron and an (electron) antineutrino are emitted.

b. Charm quark (c): `+2/3e`

Bottom quark (b): `-1/3e`

Total charge: `"Charge" = 2 xx (2/3)e + (-1/3)e = (4/3)e - (1/3)e = +1e`