You work for a start-up company that is planning to use antiproton annihilation to produce radioactive isotopes for medical applications. One way to produce antiprotons is by the reaction in proton-proton collisions. You first consider a colliding-beam experiment in which the two proton beams have equal kinetic energies. To produce an antiproton via this reaction, what is the required minimum kinetic energy of the protons in each beam?
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1. Intro to Physics Units
Introduction to Units
Problem 20b
Textbook Question
Table 44.3 shows that a Σ0 decays into a and a photon. What is the magnitude of the momentum of the photon? Is it reasonable to ignore the final momentum and kinetic energy of the ? Explain.

1
Step 1: Begin by analyzing the decay process Σ^0 → Λ^0 + γ (photon). This is a two-body decay, and conservation laws (energy and momentum) must be applied to solve the problem.
Step 2: Use the conservation of energy principle. The total energy of the Σ^0 particle before decay is equal to the sum of the energies of the Λ^0 particle and the photon after decay. Express this as: E_Σ = E_Λ + E_γ, where E_Σ is the rest energy of Σ^0, E_Λ is the rest energy of Λ^0, and E_γ is the energy of the photon.
Step 3: Use the conservation of momentum principle. Since the Σ^0 particle is initially at rest, the total momentum after decay must be zero. This means the momentum of the Λ^0 particle (p_Λ) and the photon (p_γ) must be equal in magnitude but opposite in direction: |p_Λ| = |p_γ|.
Step 4: Relate the energy of the photon to its momentum using the equation for a photon: E_γ = c * p_γ, where c is the speed of light. Combine this with the conservation of energy equation to solve for the magnitude of the photon’s momentum.
Step 5: To determine if it is reasonable to ignore the final momentum and kinetic energy of the Λ^0, compare the rest mass of Λ^0 to the energy of the photon. If the rest mass of Λ^0 is significantly larger than the photon energy, the Λ^0 will have a very small velocity and kinetic energy, making it reasonable to ignore its contribution.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conservation of Momentum
In physics, the conservation of momentum states that the total momentum of a closed system remains constant if no external forces act on it. In particle decay processes, the momentum before the decay must equal the total momentum after the decay. This principle is crucial for analyzing the decay of particles, such as the Σ^0 decaying into a Λ^0 and a photon, as it allows us to calculate the momentum of the photon based on the initial momentum of the Σ^0.
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Conservation Of Momentum
Photon Properties
A photon is a massless particle that carries electromagnetic radiation, including light. It travels at the speed of light and has energy and momentum, which can be described by the equations E = pc and p = E/c, where E is energy, p is momentum, and c is the speed of light. Understanding these properties is essential for calculating the momentum of the photon produced in the decay process and for analyzing its interactions with other particles.
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Kinetic Energy in Particle Decay
In particle decay, the kinetic energy of the resulting particles can vary significantly. The Λ^0 particle, being a baryon, has mass and thus contributes to the overall energy and momentum of the system. In some cases, if the mass of the decay products is much smaller than the mass of the original particle, it may be reasonable to ignore the kinetic energy of the lighter particles. However, this assumption must be justified based on the specific masses and energies involved in the decay.
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