Quarks + Conservation

Question 1

Strangeness

Answer 1

1
those that decay into pions only were referred to as kaons the others, such as the sigma particle in Figure 1, were found to:
• have different rest masses which were always greater than the proton’s rest mass
• decay either in sequence or directly into protons and pions.
3
strange particles are created in twos.

Question 2

The quark model

Answer 2

The properties of the hadrons, such as charge, strangeness, and rest mass can be explained by assuming they are composed of smaller particles known as quarks and antiquarks. For the hadrons studied three different types of quarks and their corresponding antiquarks are necessary. These three types are referred to as up, down, and strange quarks, and are denoted by the symbols u, d, and s, respectively.

Question 3

Quark properties

Answer 3

Charge up +2/3 Down -1/3. Strange -1/3 Antiparticles have opposite charge

Strangeness up and down 0. Strange -1 anti strange +1

Baryon number all +1/3 antiparticles -1/3

Question 4

Quark combinations

Answer 4

Mesons are hadrons, each consisting of a quark and an antiquark.

• a n° meson is a uû or dď combination. Combinations that include sś are not called pions because they decay much faster than pions.
• there are two uncharged kaons, the K° meson and the anti K° meson
• the antiparticle of any meson is a quark-antiquark pair and therefore another meson.

Question 5

Quark combinations - baryon

Answer 5

Baryons and antibaryons are hadrons that consist of three quarks for a baryon or three antiquarks for an antibaryon.
• A proton is the uud combination.
• A neutron is the udd combination.
• An antiproton is the ūūď combination.
• The sigma particle is a baryon containing a strange quark.
The proton is the only stable baryon. A free neutron decays into a proton, releasing an electron and an electron antineutrino, as in ß decay.

Question 6

First conservation rule

Answer 6

Conservation of energy and conservation of charge apply to all changes in science, not just to all particle and antiparticle interactions and decays.

Question 7

Conservation rules 2

Answer 7

Conservation rules used only for particle and antiparticle interactions and decays are essentially particle-counting rules, based on what reactions are observed and what reactions are not observed. So far, we have used the following conservation rules (in addition to energy and charge):
a Conservation of lepton numbers. In any change, the total lepton number for each lepton branch before the change is equal to the total lepton number for that branch after the change.

b Conservation of strangeness. In any strong interaction,
strangeness is always conserved.

Question 8

Baryon number

Answer 8

In any reaction, the total baryon number is conserved.