View
222
Download
2
Category
Preview:
Citation preview
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
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.
• 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
Recommended