QUARKS

HADRON CONTENT

• 2’s or 3’s ONLY!

• Baryons and Mesons

• Quarks & Antiquarks

• Baryons = Three quarks (or antiquarks) of positive or neutral charge

• Protons Neutrons and antiprotons antineutron

• Mesons = One Quark plus one Antiquark

• Pion and Antipion

THE FLAVORS. TOP

BOTTOMSTRANGE

CHARMUP

DOWN

+2/3

-1/3

PROTONS VS NEUTRONS

Proton Neutron

Different particles are made up of different mixtures of Quarks

BARYON NUMBER

• Baryon numbers are assigned to the baryons

• It is a quantum number

• The antibaryon has the opposite baryon number to its baryon counterpart

• Protons & Neutrons have +1

• Antiprotons & antineutrons have -1

• This is the same for Mesons but because they have a quark and antiquark their bryon number is 0.

• BARYON NUMBERS ARE CONSERVED IN ALL REACTIONS!

SPIN STRUCTURE

Each quark has a spin of ½

The spin can be spin up (+1/2) or spin down (-1/2)

Baryons A particle normally has a spin of ½ Sometimes however they do have a spin of 1 ½ but these particles are more energetic and highly unstable

MesonsAs they consist of quark-antiquark pairs, the spins of the quarks are in the opposing sense.

PAULI EXCLUSION PRINCIPLE

• No two fermions may occupy the same state!

• Red Green Blue

• Colour is the quantum difference between fermions

• Even though there are two up quarks in a proton their colour is different

• Therefore their spin cannot be parallel

• Thus giving them a different quantum state.

• Antired Antigreen Antiblue

• Anticolours are the only other aspect apart from charge, that is different from their quark counterparts

COLOURS

• Colours must combine to make white

(a colour neutral combination or net colour of 0)

• Combinations:

• Red Blue Gree = White

• Antired Antiblue Antigreen = White

• Red Antired = White

• Etc.

USE OF COLOUR IN FORMING BOUND QUARKS

• There are only 8 gluons

• They exist as a combination of colours and anticolours

• A Gluon has only two colours within it

• And anticolour and a colour such that combinations like red – antiblue and so on.

• There could be 9 combinations but the three red-antired, blue-antiblue, green-antigreen possiblities only give two distinct behaviours.

GLUON COLOUR

gluon

• S = -(ns – ns)

• ns = number of strange quarks

• ns = number of antistrange quarks

• (the syllabus says that the equation is the other way round i.e. (ns - ns) )

• Expressed as a quantum number

• Describes decay of particles in reactions

• Describes strong and electromagnetic reactions.

• Kept for continuity of the phrase as it predates the discovery of quarks.

• Sign for antiparticles is +1

• Sign for particles is -1

• Strangeness is conserved in strong and electromagnetic interactions

STRANGENESS

• It is not possible to observe isolated quarks. Quarks inside a hadron appear in colour combinations that result in a net colour number of 0. This is quark confinement or confinement of colour

• The force between quark and antiquark is constant no matter the separation

• Therefore the force needed to separate them gets larger the greater the separation

• Complete separation would need an infinite force

• Insisting on providing an ever increasing force would only result in the creation of a meson-antimeson pair.

CONFINEMENT

• The interaction between nucleons is the residual interaction between the quarks in the nucleons

• This is a short-range interaction.

INTERACTION BINDING NUCLEONS

QU-ARK!!What do sick ducks say?