# Particle Decay: Understanding Energies and Four-Momentum | Physics Homework

• Gargars
In summary, the conversation is about a student who is struggling with a particle physics homework assignment and is seeking help understanding the concepts involved. The homework statement involves calculating the energies and directions of photons emitted from a particle that is decaying. The student also mentions a previous problem related to particle decay and the concept of 4-momenta. The student eventually realizes that a particle can only decay into multiple particles and the conversation ends.
Gargars
Hello everybody, I'm assigned to do particle physics home, which I don't really understant because I'm a freshman and I have choosen it as a free subject. Obviously, that was a mistake. I have been reading a book, but I'm not sure if I understand everything.

## Homework Statement

A particle of rest mass M, traveling at speed v in the x-direction, decays into two photons, moving in the positive and negative x-direction relative to the original particle. What are their energies? What are the photon energies and directions if the photons are emitted in the positive and negative y-direction relative to the original particle (i.e., perpendicular to the direction of motion, in the particles rest frame).

## Homework Equations

I previously solved an equation for particle decay products energies when parent particle is ant rest. These are E1=(M^2+m1^2-m2^2)/2M, and analogicaly for E2, just -m1 squered and +m2 squered.

## The Attempt at a Solution

I'm considering photon which is moving in the positive x-direction to have less energy than the other one. Maybe I should use relatyvistic velocity addition to find these energies?

There is another problem related to the previous one.

## Homework Statement

If a massive particle decays into photons, explain using 4-momenta why it cannot decay into a single photon, but must decay into two or more. Does your explanation still hold if the particle is moving at high speed when it decays?

The four-momentum:

## The Attempt at a Solution

As far as I understand no particle can decay into another particle without nothing else. But that's not an explanation.

I get it now. Thread closed.

## 1. What is particle decay?

Particle decay is the process in which a particle breaks down into smaller particles.

## 2. How is energy involved in particle decay?

Particle decay involves a change in energy as the original particle transforms into smaller particles. This can be seen in the mass-energy equivalence equation, E=mc², where E represents the energy released during particle decay, m represents the mass of the original particle, and c represents the speed of light.

## 3. What is four-momentum and how is it related to particle decay?

Four-momentum is a mathematical quantity that describes the energy and momentum of a particle. During particle decay, the four-momentum of the original particle is conserved, meaning that the total energy and momentum of the smaller particles created from the decay must equal the original particle's energy and momentum.

## 4. How do scientists study particle decay?

Scientists study particle decay using high-energy particle accelerators, such as the Large Hadron Collider, to create and observe particles at extremely high speeds. They also use theoretical models and mathematical equations to understand the behavior of particles during decay.

## 5. Why is understanding particle decay important?

Understanding particle decay is crucial in many areas of physics, including nuclear physics, particle physics, and cosmology. It helps us understand the fundamental building blocks of the universe and how they interact with each other. Additionally, studying particle decay can lead to advancements in technology, such as medical imaging techniques and energy production.

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