Quarks and antiquarks

Question 1

When kaons were first discovered they were called V particles because

Answer 1

The cloud chamber photographs often showed v shaped tracks. They were called strange particles after investigations showed that the V tracks decay into pions only or pions and protons.

Question 2

Although these strange particles all decay through the weak interaction:

Answer 2

• Those that decay into pions only were referred to as kaons,
• The other e.g. the Σ particle: have different rest masses which are always greater the protons rest mass and decay either in sequence or directly into protons and pions.
• Strange particles are created in 2s.

Question 3

Strangeness conservation

Answer 3

Strangeness is always conserved in a strong interaction, whereas strangeness can change by 0, +1, or -1 in weak interaction.

Question 4

The Quark model

Answer 4

The properties of the hadrons, such as charge, strangeness, and rest mass can be explained by assuming they are composed of smaller particles called quarks and antiquarks.

Question 5

U quark

Answer 5

• Q = +2/3
• S = 0
• B = +1/3

Question 6

D quark

Answer 6

• Q = -1/3
• S = 0
• B = 1/3

Question 7

S quark

Answer 7

• Q = -1/3
• S = -1
• B = 1/3

Question 8

Mesons consist of:

Answer 8

A quark and antiquark

Question 9

Meson Quark composition

Answer 9

• A π⁰ meson can be any quark-corresponding antiquark combination.
• Each pair of charged mesons is a particle-antiparticle pair.
• There are two uncharged kaons, the K⁰ meson and the K̄⁰ meson.
• The antiparticles of any meson is a quark-antiquark pair and therefore another meson.

Question 10

Baryons and antibaryons are:

Answer 10

Hadrons that consist of three quarks for a baryon or three antiquarks for an antibaryon.

Question 11

Proton combination

Answer 11

uud

Question 12

Neutron combination

Answer 12

udd

Question 13

The Σ particle:

Answer 13

Is a baryon containing a strange quark.

Question 14

In β^- decay:

Answer 14

A neutron in a neutron-rich nucleus changes into a proton, releasing an electron and an electron antineutrino. In quark terms, a down quark changes into an up quark

Question 15

In β⁺ decay:

Answer 15

A proton in a proton-rich nucleus changes into a neutron, releasing a positron and an electron neutrino. In quark terms, an up quark changes into an down quark

Question 16

Conservation of energy and conservation of charge:

Answer 16

Apply to all changes in science, not just to particles and antiparticle interactions and decays.

Question 17

Conservation rules used only for particle and antiparticle interactions and decays:

Answer 17

Are essentially particle counting rules, based on what reactions are observed and what reactions are not observed.

Question 18

Conservation of lepton numbers.

Answer 18

In any change, the total lepton number for each lepton branch before the change is equal to the total lepton number for the branch after the change.

Question 19

Conservation of strangeness.

Answer 19

In any strong interaction, strangeness is always conserved.

Question 20

Baryon conservation

Answer 20

• +1 to any baryon and -1 to any antibaryon
• 0 to any meson or lepton.