A hadron is a subatomic particle made up of quarks , meaning it can feel the strong nuclear force .

What are the two classes of hadrons, and how many quarks make up each?

Baryons are made up of three quarks Mesons are made up of a quark and an anti-quark pair

Give the most common example of a baryon and a meson.

The proton and neutron are the most common baryons The pion and kaon are the most common mesons

Anti-baryons are made up of three .......... , while anti-mesons are made up of a quark and anti-quark pair.

Anti-baryons are made up of three anti-quarks , while anti-mesons are made up of a quark and anti-quark pair.

True or False? A baryon can be made from a mixture of quarks and anti-quarks, such as up, anti-down and down.

False. Baryons consist of three quarks or three anti-quarks only — mixing quarks and anti-quarks would give a non-integer baryon charge, which does not occur.

How does the quark composition of a meson's antiparticle differ from the meson itself?

Each quark becomes an anti-quark and each anti-quark becomes a quark .

What charge property is true of all baryons and mesons?

They all have integer (whole number) charges, e.g. +1 e , –2 e .

Define baryon number .

The baryon number , B , indicates the number of baryons in an interaction: baryons have B = +1, anti-baryons have B = –1, and all other particles have B = 0.

What is the baryon number of each of the up, down and strange quarks?

Each quark (u, d, s) has a baryon number of +1/3 ; each corresponding anti-quark has a baryon number of –1/3 .

The proton is the most stable baryon because it is the .......... baryon.

The proton is the most stable baryon because it is the lightest baryon.

Why can't the proton decay into a lighter, non-baryon particle?

This would reduce the baryon number from +1 to 0, violating the conservation of baryon number .

True or False? The neutron is the most stable baryon, with the longest half-life.

False. The proton is the most stable baryon with the longest half-life — it is the lightest baryon, and other baryons eventually decay into it.

What quarks make up pions, and what is their strangeness as a result?

Pions contain only up and down quarks (and their anti-quarks), giving them a strangeness of zero .

Why are pions the most stable mesons?

Pions are the lightest mesons, which makes them more stable than other mesons.

Define the role of the pion in the nucleus.

The pion is the exchange particle that mediates the strong nuclear force between baryons (nucleons) in a nucleus.

The neutral pion, π 0 , is its own .......... , but the neutral kaon is not.

The neutral pion, π 0 , is its own antiparticle , but the neutral kaon is not.

True or False? Kaons have unusually short lifetimes compared to other mesons.

False. Kaons have unusually long lifetimes compared to other mesons — this is characteristic of particles containing a strange quark.

What are the exchange particles associated with the strong force, and how do their roles differ?

The pion mediates the strong nuclear force, binding nucleons together The gluon mediates the strong interaction, binding quarks together

A lepton is a fundamental particle that is not made up of quarks. Leptons interact via the weak , gravitational and electromagnetic interactions, but not the strong force.

Name the four most common leptons.

Electron , e - Electron neutrino , ν e Muon , μ - Muon neutrino , ν μ

How does the mass of a muon compare with the mass of an electron?

The muon (about 0.1 u) is significantly heavier than the electron (about 0.0005 u).

Neutrinos have .......... charge and negligible mass.

Neutrinos have no charge and negligible mass.

Define lepton number .

The lepton number , L , is the number of leptons in an interaction: leptons have L = +1, anti-leptons have L = –1, and all other particles have L = 0. It is conserved in all interactions.

What does a muon typically decay into, and what does an anti-muon typically decay into?

A muon (μ - ) typically decays into an electron An anti-muon (μ + ) typically decays into a positron

Which interaction mediates muon decay, and how is this recognised on a Feynman diagram?

Muon decay occurs via the weak interaction , shown by the exchange of a W - boson .

True or False? Quarks are fundamental particles, so they are classified as leptons.

False. Although quarks are fundamental particles, they are not leptons — leptons do not interact via the strong force, whereas quarks do.

What three properties does every quark have, and where can their values be found?

Charge , baryon number and strangeness — their values are given on the data sheet .

An anti-quark is the antiparticle of a quark, identical except with opposite charge , baryon number and strangeness .

The strange quark has a strangeness of .......... , while the anti-strange quark has a strangeness of .......... .

The strange quark has a strangeness of –1 , while the anti-strange quark has a strangeness of +1 .

True or False? All quark flavours have a strangeness of –1.

False. Only the strange quark has a strangeness of –1 (and anti-strange +1); up and down quarks (and their anti-quarks) have a strangeness of zero .

State the quark composition of a proton and a neutron.

Proton : two up quarks and one down quark (uud) Neutron : two down quarks and one up quark (udd)

Define strange particle .

A strange particle is a particle that contains a strange or anti-strange quark, e.g. a kaon .

Through which interaction are strange particles produced, and through which do they decay?

Strange particles are produced via the strong interaction and decay via the weak interaction .

How are strange particles always produced, in terms of quark pairing?

They are always produced in quark-antiquark pairs (pair production), e.g. K + and K - .

Strangeness , S , is a quantum number that is conserved in every interaction except the weak interaction .

A particle containing an anti-strange quark has a strangeness of .......... .

A particle containing an anti-strange quark has a strangeness of +1 .

By how much can strangeness change in a weak interaction?

Strangeness can change by 0, +1 or –1 in a weak interaction.

True or False? Strangeness is conserved in every type of particle interaction, including the weak interaction.

False. Strangeness is conserved in the strong and electromagnetic interactions, but is not always conserved in the weak interaction.

A sigma baryon (S = –1) decays into a proton and pion (both S = 0). Explain how this shows the decay proceeds via the weak interaction.

Strangeness changes from –1 to 0, so it is not conserved . Since strangeness only changes in the weak interaction , the decay must proceed via this interaction.

Define particle accelerator .

A machine that collides particles at very high speeds, close to the speed of light , in order to produce new particles and reveal the inner structure of particles.

Why does particle physics research require large-scale international collaboration between scientists and engineers?

Particle accelerators are expensive and complicated to build; collaboration provides the funding and expertise needed to design, construct and operate experiments successfully.

What are the three stages by which a new particle physics theory becomes accepted?

A physicist hypothesises the existence of a new particle Experiments are carried out and combined to suggest a discovery Repeat experiments reduce experimental uncertainty and the theory is validated

The existence of the .......... was hypothesised to account for energy conservation in beta decay.

The existence of the neutrino was hypothesised to account for energy conservation in beta decay.

What extra equipment do circular particle accelerators need compared with linear accelerators, and why?

Extremely powerful superconducting magnets , to keep the high-speed particles in a circular orbit.

The Large Hadron Collider (LHC) is based at .......... , on the France and Switzerland border.

The Large Hadron Collider (LHC) is based at CERN , on the France and Switzerland border.

Around how many scientists, from how many nationalities, work at the LHC?

Around 2500 scientists from 110 nationalities work at the LHC.

True or False? A theory such as the existence of the Higgs boson is considered validated once a single detector confirms it.

False. The Higgs boson was validated because it was detected independently by both the ATLAS and CMS detectors; validation requires confirmation by repeated, independent experiments.

A LevelPhysicsAQAFlashcardsParticles & RadiationClassification of Particles

Classification of Particles (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontHadrons
Define hadron.
FrontHadrons
What are the two classes of hadrons, and how many quarks make up each?
BackHadrons
Baryons are made up of three quarks
Mesons are made up of a quark and an anti-quark pair
FrontHadrons
Give the most common example of a baryon and a meson.
BackHadrons
The proton and neutron are the most common baryons
The pion and kaon are the most common mesons

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Cards in this collection (54)

Define hadron.
A hadron is a subatomic particle made up of quarks, meaning it can feel the strong nuclear force.
What are the two classes of hadrons, and how many quarks make up each?
- Baryons are made up of three quarks
- Mesons are made up of a quark and an anti-quark pair
Give the most common example of a baryon and a meson.
- The proton and neutron are the most common baryons
- The pion and kaon are the most common mesons
Anti-baryons are made up of three .........., while anti-mesons are made up of a quark and anti-quark pair.
Anti-baryons are made up of three anti-quarks, while anti-mesons are made up of a quark and anti-quark pair.
True or False?
A baryon can be made from a mixture of quarks and anti-quarks, such as up, anti-down and down.
False.
Baryons consist of three quarks or three anti-quarks only — mixing quarks and anti-quarks would give a non-integer baryon charge, which does not occur.
How does the quark composition of a meson's antiparticle differ from the meson itself?
Each quark becomes an anti-quark and each anti-quark becomes a quark.
What charge property is true of all baryons and mesons?
They all have integer (whole number) charges, e.g. +1e, –2e.
Define baryon number.
The baryon number, B, indicates the number of baryons in an interaction: baryons have B = +1, anti-baryons have B = –1, and all other particles have B = 0.
What is the baryon number of each of the up, down and strange quarks?
Each quark (u, d, s) has a baryon number of +1/3; each corresponding anti-quark has a baryon number of –1/3.
In beta-minus decay, $n \to p + e^{-} + \bar{v_{e}}$ , show that baryon number is conserved.
Baryon number before = 1 (neutron)
Baryon number after = 1 + 0 + 0 = 1
Since both sides equal 1, baryon number is conserved.
The proton is the most stable baryon because it is the .......... baryon.
The proton is the most stable baryon because it is the lightest baryon.
Why can't the proton decay into a lighter, non-baryon particle?
This would reduce the baryon number from +1 to 0, violating the conservation of baryon number.
True or False?
The neutron is the most stable baryon, with the longest half-life.
False.
The proton is the most stable baryon with the longest half-life — it is the lightest baryon, and other baryons eventually decay into it.
What is the theorised half-life of the proton?
Around 10³² years.
What quarks make up pions, and what is their strangeness as a result?
Pions contain only up and down quarks (and their anti-quarks), giving them a strangeness of zero.
Why are pions the most stable mesons?
Pions are the lightest mesons, which makes them more stable than other mesons.
Define the role of the pion in the nucleus.
The pion is the exchange particle that mediates the strong nuclear force between baryons (nucleons) in a nucleus.
The neutral pion, π⁰, is its own .........., but the neutral kaon is not.
The neutral pion, π⁰, is its own antiparticle, but the neutral kaon is not.
How are kaons typically produced, and what quantity is conserved in this process?
Kaons are produced in pairs via the strong interaction, e.g. $p + p \to p + p + K^{+} + K^{-}$ , conserving strangeness.
Through which interaction do kaons decay, and what happens to strangeness as a result?
Kaons decay via the weak interaction, e.g. $K^{0} \to π^{+} + π^{-}$ , so strangeness is not conserved.
True or False?
Kaons have unusually short lifetimes compared to other mesons.
False.
Kaons have unusually long lifetimes compared to other mesons — this is characteristic of particles containing a strange quark.
What are the exchange particles associated with the strong force, and how do their roles differ?
- The pion mediates the strong nuclear force, binding nucleons together
- The gluon mediates the strong interaction, binding quarks together
Define lepton.
A lepton is a fundamental particle that is not made up of quarks. Leptons interact via the weak, gravitational and electromagnetic interactions, but not the strong force.
Name the four most common leptons.
- Electron, e^-
- Electron neutrino, ν_e
- Muon, μ^-
- Muon neutrino, ν_μ
How does the mass of a muon compare with the mass of an electron?
The muon (about 0.1 u) is significantly heavier than the electron (about 0.0005 u).
Neutrinos have .......... charge and negligible mass.
Neutrinos have no charge and negligible mass.
Define lepton number.
The lepton number, L, is the number of leptons in an interaction: leptons have L = +1, anti-leptons have L = –1, and all other particles have L = 0. It is conserved in all interactions.
What does a muon typically decay into, and what does an anti-muon typically decay into?
- A muon (μ^-) typically decays into an electron
- An anti-muon (μ⁺) typically decays into a positron
Which interaction mediates muon decay, and how is this recognised on a Feynman diagram?
Muon decay occurs via the weak interaction, shown by the exchange of a W^- boson.
True or False?
Quarks are fundamental particles, so they are classified as leptons.
False.
Although quarks are fundamental particles, they are not leptons — leptons do not interact via the strong force, whereas quarks do.
Name the three most common quark flavours studied at A Level.
Up, down and strange.
What three properties does every quark have, and where can their values be found?
Charge, baryon number and strangeness — their values are given on the data sheet.
Define anti-quark.
An anti-quark is the antiparticle of a quark, identical except with opposite charge, baryon number and strangeness.
The strange quark has a strangeness of .........., while the anti-strange quark has a strangeness of ...........
The strange quark has a strangeness of –1, while the anti-strange quark has a strangeness of +1.
True or False?
All quark flavours have a strangeness of –1.
False.
Only the strange quark has a strangeness of –1 (and anti-strange +1); up and down quarks (and their anti-quarks) have a strangeness of zero.
State the quark composition of a proton and a neutron.
- Proton: two up quarks and one down quark (uud)
- Neutron: two down quarks and one up quark (udd)
State the quark composition of the three types of pion.
- π⁺: up and anti-down ( $u \bar{d}$ )
- π^-: anti-up and down ( $\bar{u} d$ )
- π⁰: up and anti-up, or down and anti-down
State the quark composition of the three types of kaon.
- K⁺: up and anti-strange ( $u \bar{s}$ )
- K^-: anti-up and strange ( $\bar{u} s$ )
- K⁰: down and anti-strange, or anti-down and strange
Define strange particle.
A strange particle is a particle that contains a strange or anti-strange quark, e.g. a kaon.
Through which interaction are strange particles produced, and through which do they decay?
Strange particles are produced via the strong interaction and decay via the weak interaction.
How are strange particles always produced, in terms of quark pairing?
They are always produced in quark-antiquark pairs (pair production), e.g. K⁺ and K^-.
Define strangeness.
Strangeness, S, is a quantum number that is conserved in every interaction except the weak interaction.
A particle containing an anti-strange quark has a strangeness of ...........
A particle containing an anti-strange quark has a strangeness of +1.
By how much can strangeness change in a weak interaction?
Strangeness can change by 0, +1 or –1 in a weak interaction.
True or False?
Strangeness is conserved in every type of particle interaction, including the weak interaction.
False.
Strangeness is conserved in the strong and electromagnetic interactions, but is not always conserved in the weak interaction.
A sigma baryon (S = –1) decays into a proton and pion (both S = 0). Explain how this shows the decay proceeds via the weak interaction.
Strangeness changes from –1 to 0, so it is not conserved.
Since strangeness only changes in the weak interaction, the decay must proceed via this interaction.
Define particle accelerator.
A machine that collides particles at very high speeds, close to the speed of light, in order to produce new particles and reveal the inner structure of particles.
Why does particle physics research require large-scale international collaboration between scientists and engineers?
Particle accelerators are expensive and complicated to build; collaboration provides the funding and expertise needed to design, construct and operate experiments successfully.
What are the three stages by which a new particle physics theory becomes accepted?
- A physicist hypothesises the existence of a new particle
- Experiments are carried out and combined to suggest a discovery
- Repeat experiments reduce experimental uncertainty and the theory is validated
The existence of the .......... was hypothesised to account for energy conservation in beta decay.
The existence of the neutrino was hypothesised to account for energy conservation in beta decay.
What extra equipment do circular particle accelerators need compared with linear accelerators, and why?
Extremely powerful superconducting magnets, to keep the high-speed particles in a circular orbit.
The Large Hadron Collider (LHC) is based at .........., on the France and Switzerland border.
The Large Hadron Collider (LHC) is based at CERN, on the France and Switzerland border.
Around how many scientists, from how many nationalities, work at the LHC?
Around 2500 scientists from 110 nationalities work at the LHC.
True or False?
A theory such as the existence of the Higgs boson is considered validated once a single detector confirms it.
False.
The Higgs boson was validated because it was detected independently by both the ATLAS and CMS detectors; validation requires confirmation by repeated, independent experiments.

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