Quarks and leptons (topic 2) Flashcards
What are cosmic rays?
High-energy particles (protons or small nuclei) travelling through space, from stars
What happens when cosmic rays enter the atmosphere?
They collide with gas atoms in the atmosphere, creating photons, and new short-lived particles and anti-particles
What are the three short-lived particles created by cosmic rays reaching earth’s atmosphere or protons colliding at high speeds?
Muon, pion, kaon
What are the characteristics of the muon? (2)
- negatively charged
- rest mass 200x larger than an electron
What are the characteristics of a pion? (2)
- Can have positive, negative or neutral charge
- rest mass greater than muon but less than proton
What are the characteristics of a kaon? (3)
- can have positive, negative or neutral charge
- rest mass greater than pion but less than proton
What is created by kaon decay? (2)
1) pions
2) muon antineutrino/neutrino antimuon pair
What is created by CHARGED pion decay?
muon antineutrino/neutrino antimuon pair
What is created by pion(0) decay?
high-energy photons
What is creates by muon decay?
electron and antineutrino
Hadrons (definition)
Particles/antiparticles that can interact through strong interaction
and are made up of quarks
Leptons (definition)
Particles/anitparticles that do NOT interact through the strong interaction and are NOT made up of quarks
What is conserved in ALL decays? (5)
Energy, momentum, charge, lepton number, baryon number
How do we find the rest energy of products of interactions?
Rest energy of products = total energy before - kinetic energy of products
Baryon (definition)
Hadrons that decay into protons (directly or indirectly)
Meson (definition)
Hadrons that cannot decay into protons (kaons and pions)
What happens when leptons collide?
A quark and its antiqaurk are produced moving in opposite direction, producing a “shower” of hadrons in each direction.
How are electron neutrinos and muon neutrinos different?
Muon neutrinos can only create muons. They cannot create electrons when interacting with protons/neutrons.
What do current experiments indicate about leptons? How do we come to this conclusion?
Leptons appear to be fundamental, because they cannot break down into non-leptons
Why can a neutrino only change into its corresponding lepton, not its corresponding antilepton?
Lepton number must be conserved. Anti leptons have lepton number -1, so must produce a particle with lepton number -1 in a lepton-hadron interaction.
What happens in muon decay?
A muon becomes a muon neutrino/antimuon to antineutrino, and a electron/positron is created to conserve the charge + relevant (anti)neutrino. A muon cannot become an antimuon neutrino because lepton number or charge could not be conserved.
How does lepton conservation work?
Leptons have lepton number +1, antileptons have lepton number -1. Electrons and muons + their respective neutrinos must be considered respectively as muon neutrinos can’t become electrons and vice versa.
How is a kaon different from other strange particles?
It only decays into pions and has a rest mass lower than that of a proton.
What is true for all strange particles?
They are produced in twos and decay through the weak interaction
How is strangeness conserved? (2)
Always conserved in strong interactions
Can change by +1, -1 or not change during weak interactions
Properties of an u quark (3)
Charge = +2/3
Strangeness = 0
Baryon number = +1/3
Properties of a d quark (3)
Charge = -1/3
Strangeness = 0
Baryon number = +1/3
Properties of an s quark (3)
Charge = -1/3
Strangeness = -1
Baryon number = +1/3
Meson quark combinations
A quark-anti-quark pair
Baryon quark combinations
Three quarks OR three antiquarks
Which baryons are stable?
Only the proton - neutrons outside the nucleus will decay into protons through beta(-)
Kaon quark combinations
Kaons must include an (anti)/strange quark. Positive and K(0) have +1S, while anti-positive and anti(K(0)) have -1S.
Pion quark combinations
Only contain anti(up/down) quarks. All antimesons are also mesons, so pion+ is the antimeson of pion- and there are two pion(0)s.
Which baryon is the only one to include a strange particle?
Sigma
Where does beta(-) decay happen? Where does beta(+) decay happen?
B- = in a neutron-rich nucleus
B+ = in a proton-rich nucleus
What happens in terms of quarks during beta- decay?
A down quark changes to an up quark
What must be conserved in STRONG interactions? (6)
Charge, energy, momentum, lepton number, baryon number, and strangeness
Why might number of quarks NOT be conserved in an interaction?
Annihilation or pair production
