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. +2/3 -1/3

PROTONS VS NEUTRONS ProtonNeutron 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 Mesons As 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 = -(n s – n s ) n s = number of strange quarks n s = number of antistrange quarks (the syllabus says that the equation is the other way round i.e. (n s - n s ) ) 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?