1.6 - HADRONS AND LEPTONS Flashcards
What particles are affected by the strong nuclear force?
Hadrons only
What is the exchange particle of gravity?
Graviton
What particles are affected by gravity?
All types
Is particle physics concerned with gravity?
Not really - it is usually ignored because it is very feeble unless large masses are involved.
What is the mass of a W boson?
About 100 times that of a proton.
Compare and explain the ranges of a W boson and a photon.
- W boson - Very short range because it has a large mass. This means it requires a lot of energy to create and can’t travel very far.
- Photon - Infinite range because it has zero mass.
What are hadrons?
Particles that feel the strong nuclear force. They are not fundamental.
What are hadrons made of?
Quarks
Are hadrons fundamental particles?
No, they are made of quarks.
What are the two types of hadrons?
- Baryons
* Mesons
What is the difference between baryons and mesons?
2 REASONS
- Baryons - Made of 3 quarks and decay into a proton directly or indirectly
- Mesons - Made of a quark and antiquark and do NOT decay into a proton
Name some baryons.
- Protons
- Neutrons
- Other particles (e.g. Sigmas)
What is the only stable baryon?
Proton - this means all baryons will decay in sequence and eventually form a proton.
Are antibaryons found in ordinary matter?
No, because they annihilate with baryons.
What values are particles given in baryon number conservation?
- Baryons = +1
- Antibaryons = -1
- Other particles = 0
What are some examples of antibaryons?
- Antiprotons
* Antineutrons
Why does beta decay happen?
Neutrons are not stable baryons, but protons are, so a neutron will decay into a proton.
Are mesons stable?
No
What are the different types of meson?
Pions and kaons
What is another name for a pion?
Pi-meson
What is another name for a kaon?
K-meson
What is the difference between pions and kaons?
- Pions - Lighter, less unstable, not strange
* Kaons - Heavier, more unstable, strange, very short lifetime
What is the antiparticle for π+
π-
What is the antiparticle for π0
Itself
What happens to kaons?
They decay into pions.
Where were pions and kaons seen?
Cosmic rays interact with molecules in the atmosphere and produce “showers” of lots of high-energy particles, including pions and kaons. = cosmic ray showers
How did scientists find pions and kaons?
How are they seen now?
Cloud chamber used to observe the tracks of the particles.
Now:
Two Geiger counters on top of each other with absorbing lead between them. If both counters detect radiation simultaneously it is likely to be a particle from a cosmic ray shower (rather than just random noise like background radiation)
How do mesons interact with baryons?
Through the strong force.
What are the general rules for determining the type of interaction in a reaction?
- If any leptons involved at all -> Weak interaction
- If strangeness isn’t conserved -> Weak interaction
- All others -> Strong interaction
What are leptons?
Particles that do not feel the strong interaction. They are fundamental.
What are the different leptons?
- Electrons
- Muons
- Neutrinos
- Tau
What happens to muons?
The eventually decay into electrons. This is because muons are unstable.
What can muons be described as?
Heavy electrons.
What is the mass and charge of neutrinos?
- Mass - Almost zero
* Charge - Zero
How does lepton conservation work?
- There are 3 generations of lepton number - electron, muon and tau
- Each lepton number must be conserved separately
- Each normal lepton and its respective neutrino is given a lepton number of +1
- Each anti-lepton and its respective antineutrino is given a lepton number of -1
What are the symbols for each lepton number?
- Electron lepton number = Le
- Muon lepton number = Lmuon
- Tau lepton number = Lt
What are antiparticles of hadrons made from?
Antiquarks
How do strange particles (e.g. kaons) interact?
- Created by the strong interaction
* Decay via the weak interaction
Strange particles are always produced in pairs (e.g. K+ and K-). Why?
The strangeness cancels out to become 0, so that strangeness is conserved. Therefore, the reaction is a strong interaction.
What are the types of quark?
- Up
- Down
- Strange
What is the charge of an up quark?
+2/3
What is the charge of a down quark?
-1/3
What is the charge of a strange quark?
-1/3
What is the charge of an anti-up antiquark?
-2/3
What is the charge of an anti-down antiquark?
+1/3
What is the charge of an anti-strange antiquark?
+1/3
What is the strangeness of a strange quark?
-1
What is the strangeness of an anti-strange antiquark?
+1
What is unusual about strangeness?
- It is not ALWAYS conserved
- Strange quarks are given a strangeness of -1 and anti-strange antiquarks are given a strangeness of +1.
In weak force: it is not usually conserved and can change by +1, -1, or 0
What quarks make up a proton?
uud
What quarks make up an antiproton?
anti-u, anti-u, anti-d
What quarks make up a neutron?
udd
What quarks make up an antineutron?
anti-u, anti-d, anti-d
What are baryons made of?
3 quarks
What are mesons made of?
A quark and an antiquark
What is the antiparticle of a pi-plus meson?
A pi-minus meson.
Remember to revise the diagram on mesons.
Pg 14 of the revision guide
What is a weak interaction in terms of quarks?
A weak interaction is something that changes the quark type (e.g. A neutron (udd) turning into a proton (uud))
What properties are conserved in an interaction?
- Charge
- Baryon number
- Strangeness (only in strong interactions)
- Lepton number (all 3 generations separately)
How is baryon number conserved in pair production?
How is charge conserved in pair production and neutron decay (e.g. beta minus)?
Why is strangeness only conserved in strong interaction?
You can change the type of quark in weak interactions.
In strong interactions the strange quarks have to be conserved throughout.
Can a quark exist on its own?
No.
What is quark confinement?
The idea that quarks cannot exist not their own.
Through which interaction do hadrons tend to decay?
Weak
Describe the mass, range and charge of a W boson.
- Non-zero rest mass
- 0.001fm range
- Can be positively or negatively charged
What are the quarks in a K0 meson?
- Anti-s
* d
What are the quarks in an anti-K0 meson?
- s
* Anti-d
