Particle Interactions & Conservation (Edexcel A Level Physics): Flashcards
Exam code: 9PH0
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- FrontThe Standard Model
Define hadron.
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Define hadron.
A hadron is a particle made up of quarks that interacts via the strong nuclear force. Baryons and mesons are both hadrons.
How many quarks make up a baryon and a meson, and give an example of each?
Baryon: 3 quarks — e.g. proton, neutron
Meson: a quark–antiquark pair — e.g. pion, kaon
Define lepton.
A lepton is a fundamental (elementary) particle that is not made of quarks and does not interact via the strong nuclear force.
Name the four most common leptons.
The electron (e-), the electron neutrino (ve), the muon (μ-) and the muon neutrino (vμ).
How does the muon compare with the electron?
The muon is about 200 times more massive than the electron, but both carry a charge of -1*e*.
What are the properties and role of the photon?
The photon is uncharged and has zero mass. It is the exchange particle that mediates the electromagnetic interaction.
The symmetry of the standard model predicted a third generation of quarks: the .......... and .......... quarks.
The symmetry of the standard model predicted a third generation of quarks: the top and bottom quarks.
True or False?
Leptons interact via the strong nuclear force.
False.
Leptons do not interact via the strong nuclear force. Only hadrons (baryons and mesons) feel the strong force.
Define antiparticle.
An antiparticle is identical to its matter counterpart but has the opposite charge, while its mass stays the same.
How do a particle and its antiparticle compare?
Same: mass and rest mass-energy
Different: opposite electric charge
A neutral particle, such as a neutron, neutrino or photon, is its own ...........
A neutral particle, such as a neutron, neutrino or photon, is its own antiparticle.
True or False?
An antiparticle has less mass than its matter particle.
False.
A particle and its antiparticle have identical mass and rest mass-energy; only the charge is opposite.
Define rest mass-energy.
The rest mass-energy of a particle is the energy equivalent to the mass of the particle at rest.
How is an antiparticle usually named and written?
It has the same name with the prefix 'anti-' and a bar (line) above the particle's symbol. The electron is an exception.
Which three quantum numbers are always conserved in particle interactions?
Charge (Q), baryon number (B) and lepton number (L).
Define baryon number (B).
The baryon number is the number of baryons in an interaction. Baryons have B = +1, anti-baryons B = -1 and non-baryons B = 0.
Define lepton number (L).
The lepton number is the number of leptons in an interaction. Leptons have L = +1, anti-leptons L = -1 and non-leptons L = 0.
What is the baryon number of a quark and of an antiquark?
Each up, down and strange quark has a baryon number of +1/3, and each corresponding antiquark has -1/3.
An interaction that does not conserve charge, baryon number or lepton number is ...........
An interaction that does not conserve charge, baryon number or lepton number is not allowed.
State the charge Q of a proton, an electron and an up quark.
Proton: Q = +1
Electron: Q = -1
Up quark: Q = +2/3
True or False?
An electron has a lepton number of -1.
False.
The electron has a lepton number of +1. It is the positron that has a lepton number of -1.
Which five quantities must be conserved in every particle interaction?
Charge (Q)
Baryon number (B)
Lepton number (L)
Energy (mass-energy)
Momentum
How do you check whether a particle interaction can occur?
Check that each conserved quantum number (Q, B, L), along with energy and momentum, is equal on both sides of the equation.
If even one quantum number, apart from .......... in weak interactions, is not conserved, the interaction cannot occur.
If even one quantum number, apart from strangeness in weak interactions, is not conserved, the interaction cannot occur.
Two protons collide to give two protons, a positive pion (π+) and an antiproton. Charge is conserved, so why is the reaction not permitted?
Because baryon number is not conserved: the left side has B = 2, but the right side has B = 1 + 1 + 0 + (-1) = 1.
What values can quantum numbers such as Q, B and L take?
Only discrete values — for example 0, +1, -1 or ½ — never continuous ones.
True or False?
A particle interaction is permitted as long as charge is conserved.
False.
Every conserved quantity — charge, baryon number, lepton number, energy and momentum — must balance. Conserving charge alone is not enough.
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