Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 2 Quarks and Ieptons (2.2 (Classifying particles and antiparticles…
Chapter 2
Quarks and Ieptons
2.1
Space Invaders
Cosmic rays
- high energy particles (fast moving protons or small nuclei) that travel through space from stars- create short-lived particles, anti-particles and photons when they enter the Earth's atmosphere
New particles discovered
Muon (μ)
or Heavy electron - negatively charges particle
Rest mass over 200x that if an electron
Pion (π)
or π meson- Can be positive, negative or neutral
Rest mass greater than muon but less than proton
Kaon (K)
or K meson- Can be positive, negative or neutral
Rest mass greater than pion but less than proton
A Strange Puzzle
Pions and kaons are produced in twos through the
strong interaction
Decay of kaons took longer than expected and included pions in the product- Kaon must decay via
weak interaction
(strangeness not conserved)
Kaons known as
strange particles
due to its properties
Kaon decay
- 1) Pions
2) Muon and antineutrino
3) Antimuon and neutrino
Charged pion decay
- 1) Nuon and antineutrino
2) Antimuon and neutrino
Neutral pion decay
- High energy photons
Muon decay
- 1) Electron and antineutrino
Antimuon decay
- 1) Positron and neutrino
2.2
Classifying particles and antiparticles
π+ meson and π- meson are often produced in pairs, led to conclusion they were a particle-antiparticle pair, same for Kaon
Anti-particle symbol= particle symbol with bar above
Except antimuon- μ+ and positron- e+
Hadrons
-Particles and antiparticles that interact through the strong interaction e.g. Protons, Neutrons, π mesons, K mesons
Decay through weak interaction
except proton which is stable
Leptons
- Particles and antiparticles that don't interact through the strong interaction e.g Electrons, muons and neutrinos
Energy
Total rest energy of products = total energy before - Ek of products
Baryons and mesons
Hadrons
split into two groups
baryons
and
mesons
Baryons
- protons and all other hadrons that decay into protons directly or indirectly
Mesons
- Hadrons that don't include protons in their decay products
Baryons and mesons are made up of smaller particles called
Quarks
and
antiquarks
2.3
Lepton collisions
Lepton and antileptons can interact to produce hadrons- produces a quark and a corresponding anti-quark- move away in opposite directions producing a shower of hadrons
Neutrino types
Neutrinos and antineutrinos from beta decay are different to neutrinos produced by muon decays
Muon neutrino-
Electron neutrino-
Lepton rules
Leptons can change into other leptons through the weak interaction and can be produced or annihilates in particle-antiparticle interactions
1) Interaction between a lepton and a hadron, a neutrino or an antineutrino
Electron neutrino can interact with a neutron to produce a proton and electron
But it cannot change into an antiproton and positron because although charge is conserved, lepton number LHS= +1 +0= +1 RHS= 0+ -1= -1
2) Muon decay- muon changes into a muon neutrino, electron is created and an antineutrino
e.g.
Lepton number must be conserved in any change
Lepton number = +1 for lepton, -1 for antilepton, 0 for non-lepton
Muon can only change into a muon neutrino not a muon antineutrino
Electron can only be created with an electron antineutrino
2.4
Strangeness
Strange particles decay through weak interaction
Strange particles created in twos
Other strange particles (not kaon)- have different rest masses- always greater than proton's- decay either in sequence or directly into protons and pions
Quark model
3 types -
up, down, strange
Anti- quarks have opposite charge, strangeness and baryon number to its counterpart
Quark combinations
Mesons
Consist of a quark and anti-quark
π0 - quark- corresponding antiquark combination
Charged meson- particle- antiparticle pair
Antiparticle of any meson is a quark- antiquark pair and therefore another meson
Baryons and antibaryons
Hadrons consist of 3 quarks or 3 antiquarks
Proton
- uud
Neutron
-udd
Antiproton
-
Σ particle is a baryon containing a strange quark
Beta- decay
- down quark->up quark
Beta + decay
- up quark-> down quark
2.5
Particles and properties
Conservation of energy and charge
-
Conservation rules are only used for particle and antiparticle interaction and decays
Lepton number is conserved
Strangeness is conserved in any strong interaction
- change in strangeness can only occur in a weak interaction
In any reaction baryon number is conserved
-
1/3= quark, -1/3 = antiquark 0= lepton
