Antiparticles, pair production and annihilation

Particle accelerators produce beams of high speed charged particles which are used to investigate particle collisions. New particles are created during the collisions.

In the Large Hadron Collider (LHC), protons are maintained in a circular path by the force exerted on the protons due to a magnetic field.

The magnetic flux density required to maintain the protons in a circular path increases as the kinetic energy of the protons increases.

Explain why.

Calculate the magnetic flux density required to maintain the protons in the LHC when the protons are travelling at a speed of 3.0 10⁷m s^–1.

circumference of LHC = 27 km

A maximum of 13 600 GeV of energy is available to create a new particle.

Calculate the theoretical maximum mass, in kg, of the new particle.

*(b) Fifty years ago, fixed‑target collision experiments were carried out at the Stanford Linear Accelerator Centre (SLAC). In these experiments, high speed particles were made to collide with a stationary target.

Currently, colliding beam experiments are carried out at SLAC. In these experiments, high speed particles travelling in opposite directions are made to collide head‑on.

For a given total energy in the collision, colliding beam experiments allow particles to be created with a larger mass than could be created in a fixed‑target experiment.

Explain why colliding beam experiments allow a new particle with the larger mass to be created. You should consider how the conservation of energy and the conservation of momentum apply to each type of collision.

Beams of antiprotons are often used in particle physics experiments.

Show that the rest mass of an antiproton is about 900 MeV / c².

A delta particle decays into a proton and a pion.

The diagram shows tracks in a particle detector formed when the delta particle decays.

State why it can be concluded from the diagram that the delta particle is neutral.

Deduce the charge on the pion.

Complete the particle equation for the decay of the delta (Δ⁰) particle.

State why the delta particle must be classified as a baryon based on the evidence of its decay.

Explain how the momentum of the proton compares with the momentum of the pion.

The mass of the delta particle is 1232 MeV/c².

Calculate the mass of the delta particle in kg.

The mass of the proton is 939 MeV/c² and the mass of the pion is 139 MeV/c².

Explain why the sum of the masses of the two particles after the decay is not equal to the mass of the delta particle.

A particle has a mass of 1 u and a charge of −1.610⁻¹⁹C.

Which of the following could be the particle?

The π⁻ particle has a mass of 140 MeV / c².

Which row of the table is correct for the antiparticle of a π⁻?

Which row of the table summarises the mass and charge of an antineutron?

Which row of the table summarises the mass and charge of an antineutron?

An example of this decay is given by the equation

The discovery of the Higgs particle was an important contribution to our understanding of particle physics.

Describe the standard model for subatomic particles. You should identify the fundamental particles and the composition of the particles we can observe.

The mass of the Higgs particle is 2.2 10^–25 kg.

Calculate this mass in GeV/c².

The Higgs particle was discovered using the Large Hadron Collider (LHC) in 2012. Two beams of very high energy protons, moving in opposite directions, were made to collide.

Explain the need for such high energy collisions.

The beams of protons are contained within a ring of superconducting magnets.

Calculate the momentum of a proton in a beam.

magnetic field strength = 8.3 T circumference of the ring = 27 km

State the total momentum of the products of the collision between the two beams of protons.

The LHC accelerates protons until they gain energies of about 7 TeV.

A student used the equation E = to predict the energy of a proton in the beam, using the momentum calculated in (c)(ii), but found the energy was far higher than 7 TeV.

Explain why.

The neutral lambda Λ⁰ particle is a baryon of mass 1116 MeV/c² and contains one strange quark.

The table shows quarks and their relative charge.

State, with justification, the quark content of a Λ⁰ particle.

Calculate the mass of the Λ⁰ particle in kg.

A student suggests five ways a Λ⁰ particle might decay. These are

Deduce which of these decay processes are not possible.

Lambda particles were first detected in experiments which made use of cosmic rays entering the atmosphere. Cosmic rays are mainly high‑energy protons which have a mass less than that of a lambda particle.

Explain why a cosmic ray could lead to the creation of a lambda particle.

The Λ⁰ particle cannot be directly observed in particle experiments, however some of the decay products can.

Explain why the Λ⁰ particle cannot be directly observed but information about it can be obtained by studying its decay particles.