Particle Interactions & Conservation (Edexcel International A Level (IAL) Physics): Flashcards
Exam code: YPH11
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- FrontThe Standard Model
Define baryon.
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Cards in this collection (25)
Define baryon.
A baryon is a hadron made up of three quarks, for example the proton and neutron.
Define meson.
A meson is a hadron made up of a quark-antiquark pair, for example pions and kaons.
Which fundamental force do hadrons interact via, and why don't leptons experience this force?
Hadrons interact via the strong nuclear force because they are made of quarks. Leptons do not experience the strong force, as they contain no quarks.
What is the quark composition of an anti-meson, compared to the original meson?
An anti-meson is still a quark-antiquark pair. The quark becomes the antiquark and the antiquark becomes the quark.
A baryon cannot contain a mix of quarks and antiquarks, because this would give a baryon number that is not a ...........
A baryon cannot contain a mix of quarks and antiquarks, because this would give a baryon number that is not a whole number (integer).
True or False?
Photons are charged particles that mediate the strong nuclear force.
False.
Photons are uncharged, have zero mass, and mediate the electromagnetic interaction, not the strong force.
The symmetry of the Standard Model predicted a third generation of quarks before they were discovered. Name these two quarks.
The top quark and the bottom quark.
Define antimatter.
Antimatter particles are identical to their matter counterparts, but have the opposite electric charge.
How does the mass and rest mass-energy of an antiparticle compare to its matter counterpart?
They are identical — the same mass and the same rest mass-energy, despite the opposite charge.
Which particles are their own antiparticle, and why?
Neutral particles, such as the neutron, neutrino and photon, are their own antiparticle, because they have no charge to reverse.
What is the antiparticle of the electron called, and why is this an exception to the usual naming convention?
It is called the positron. Unlike other antiparticles, which are named 'anti-' plus the particle name, the electron's antiparticle has its own unique name.
True or False?
A proton and an antiproton have different masses but identical charge.
False.
A proton and antiproton have identical mass but opposite charge.
Apart from the electron, an antiparticle has the same name as its matter counterpart with the prefix ...........
Apart from the electron, an antiparticle has the same name as its matter counterpart with the prefix 'anti-'.
Define baryon number.
The baryon number (B) is a quantum number equal to +1 for baryons, –1 for anti-baryons, and 0 for particles that are not baryons.
Define lepton number.
The lepton number (L) is a quantum number equal to +1 for leptons, –1 for anti-leptons, and 0 for particles that are not leptons.
What is the baryon number of an up, down or strange quark?
Each has a baryon number of +1/3 (their antiquarks have –1/3).
Which three quantum numbers are always conserved in a particle interaction?
Charge (Q), baryon number (B) and lepton number (L).
True or False?
The electron has a lepton number of –1 because it has a negative charge.
False.
The electron has a lepton number of +1; it is the positron that has a lepton number of –1. Charge and lepton number are separate quantum numbers.
A particle interaction that does not conserve charge, baryon number or lepton number is not .......... by the laws of physics.
A particle interaction that does not conserve charge, baryon number or lepton number is not allowed by the laws of physics.
What must be true of every conserved quantum number (Q, B, L) on both sides of a particle interaction equation, for the interaction to be permitted?
Each conserved quantum number must be equal on both sides of the equation.
In a proposed reaction, two protons collide to produce two protons, a positive pion and an antiproton. Why is this reaction not permitted, even though charge is conserved?
Baryon number is not conserved: the left side has B = 2, but the right side gives B = 1 + 1 + 0 + (–1) = 1.
Define quantum number.
A quantum number (such as charge, baryon number or lepton number) is a property of a particle that can only take discrete values (e.g. 0, +1, –1, 1/2), and must be conserved in an interaction.
Which quantum number is the exception that need not be conserved in weak interactions?
Strangeness — unlike charge, baryon number and lepton number, strangeness is not required to be conserved in weak interactions.
True or False?
If a particle interaction conserves charge and lepton number but not baryon number, it is still permitted.
False.
All conserved quantum numbers must be equal on both sides. Failing to conserve even one (apart from strangeness in weak interactions) means the interaction cannot occur.
In a particle interaction, quantum numbers can only take .......... values, such as 0, +1, –1 or 1/2.
In a particle interaction, quantum numbers can only take discrete values, such as 0, +1, –1 or 1/2.
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