3.2.1.5. - 3.2.1.6. - 3.2.1.7.
3 ways of categorising particles?
- hadrons
- leptons
- gauge bosons
Hadrons
General properties of all hadrons?
- they interact through all 4 fundamental force of interactions (including the strong nuclear)
- all hadrons are massive, strong and heavy
- OBVS a hadron can only interact through the electromagnetic force if it's charged (pi zero
mesons can't e.g.)
- only the proton is stable → the rest of the hadrons decay through the weak
interaction
2 subcategories of hadrons? Examples for each? Their antiparticle? No. of quarks
they’re composed of?
1) baryons
- 3 quarks
→ neutrons, antineutrons
→ protons, antiprotons
2) mesons
- 2 quarks (a quark and an antiquark {they don't have to be a corresponding pair})
- kaons
~ K+ antiparticle: K-
~ K0 antiparticle: K bar 0 (anti K0)
- pions
~ pi+ antiparticle: pi-
~ pi0 antiparticle: pi0 (itself) (meaning: for pi0 there are 2 possible quark
compositions)
Is pion = pi meson?
- yes
What does it suggest that all hadrons can be further broken down into quarks?
- quarks are fundamental particles
What is true for all baryons, except for the proton?
- they’re all unstable
→ they all decay to become a proton
⇒ so basically, the neutron will always try to decay into a proton
Baryon no. def.?
- the no. of baryons in a particle interaction
- baryons have a +1 number, whereas antibaryons have a -1 number
→ this property has to be conserved in an interaction (gotta be the same on
either side)
Use of baryon no.?
- allows us to predict whether a particle interaction can happen → if the baryon
no. is not the same on both sides of the interaction → can’t happen
What is true for all mesons?
- they are ALL unstable - no exception
, Mesons in order of increasing mass?
- pions < kaons
How do mesons and baryons interact?
- via the strong nuclear force ← as hadrons feel the strong nuclear force
Hadron family tree?
Describe pion interactions?
EITHER…
…swap protons with neutrons
OR…
…swap neutrons with protons ⇐ both of these leave the baryon no. unchanged
Decay modes of a pion?
IF charged (+/-):
option 1) decays into a muon + antineutrino
option 2) decays into an antimuon + neutrino
IF not charged:
decays into high energy photons
Decay modes of a kaon?
option 1) decays into multiple pions
option 2) decays into muon + antineutrino
option 3) decays into antimuon + neutrino
What hadron will never be the decay product of mesons?
- proton ← bcs mesons are not baryons
Leptons
General properties of all leptons?
- all leptons are light and weak
- they interact through all 4 fundamental forces, except for the strong nuclear (as they're not
found in the nucleus)
- OBVS a lepton can only interact through the electromagnetic force if it's charged (neutrinos
can't)
Examples of leptons?
--> electron, positron
--> electron neutrino, antielectron neutrino
--> muon, antimuon
--> muon neutrino, antimuon neutrino
3 ways of categorising particles?
- hadrons
- leptons
- gauge bosons
Hadrons
General properties of all hadrons?
- they interact through all 4 fundamental force of interactions (including the strong nuclear)
- all hadrons are massive, strong and heavy
- OBVS a hadron can only interact through the electromagnetic force if it's charged (pi zero
mesons can't e.g.)
- only the proton is stable → the rest of the hadrons decay through the weak
interaction
2 subcategories of hadrons? Examples for each? Their antiparticle? No. of quarks
they’re composed of?
1) baryons
- 3 quarks
→ neutrons, antineutrons
→ protons, antiprotons
2) mesons
- 2 quarks (a quark and an antiquark {they don't have to be a corresponding pair})
- kaons
~ K+ antiparticle: K-
~ K0 antiparticle: K bar 0 (anti K0)
- pions
~ pi+ antiparticle: pi-
~ pi0 antiparticle: pi0 (itself) (meaning: for pi0 there are 2 possible quark
compositions)
Is pion = pi meson?
- yes
What does it suggest that all hadrons can be further broken down into quarks?
- quarks are fundamental particles
What is true for all baryons, except for the proton?
- they’re all unstable
→ they all decay to become a proton
⇒ so basically, the neutron will always try to decay into a proton
Baryon no. def.?
- the no. of baryons in a particle interaction
- baryons have a +1 number, whereas antibaryons have a -1 number
→ this property has to be conserved in an interaction (gotta be the same on
either side)
Use of baryon no.?
- allows us to predict whether a particle interaction can happen → if the baryon
no. is not the same on both sides of the interaction → can’t happen
What is true for all mesons?
- they are ALL unstable - no exception
, Mesons in order of increasing mass?
- pions < kaons
How do mesons and baryons interact?
- via the strong nuclear force ← as hadrons feel the strong nuclear force
Hadron family tree?
Describe pion interactions?
EITHER…
…swap protons with neutrons
OR…
…swap neutrons with protons ⇐ both of these leave the baryon no. unchanged
Decay modes of a pion?
IF charged (+/-):
option 1) decays into a muon + antineutrino
option 2) decays into an antimuon + neutrino
IF not charged:
decays into high energy photons
Decay modes of a kaon?
option 1) decays into multiple pions
option 2) decays into muon + antineutrino
option 3) decays into antimuon + neutrino
What hadron will never be the decay product of mesons?
- proton ← bcs mesons are not baryons
Leptons
General properties of all leptons?
- all leptons are light and weak
- they interact through all 4 fundamental forces, except for the strong nuclear (as they're not
found in the nucleus)
- OBVS a lepton can only interact through the electromagnetic force if it's charged (neutrinos
can't)
Examples of leptons?
--> electron, positron
--> electron neutrino, antielectron neutrino
--> muon, antimuon
--> muon neutrino, antimuon neutrino
