What is the equation for finding the energy of a photon in a Σ0 decay?

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Homework Statement

The sigma Baryon Σ0 is at rest and decays to form an Λ0 and a ɣ photon.

Homework Equations

Mass of Σ0 is 1193 MeV/c^2
Mass of Λ0 is 1116 MeV/C^2

The Attempt at a Solution

K obviously since the Σ0 is at rest, momentum must be conserved and the Λ0 and ɣ go in completely opposite directions to each other.

Since the Σ0 weighs more than the Λ0, I can assume it's rest mass go towards the rest mass of the Λ0 and provides kinetic energy for the Λ0.. Also giving energy out as the ɣ.

But the ɣ has no mass. So it's energy is it's momentum. But I've forgotten how to account for that. What equations do I use to found out how much energy the photon has.

The only thing I have going is that 77MeV/c^2 is shared between the kinetic energy of the Λ0 and the total energy of the ɣ photon, but I don't know how to work out HOW MUCH is shared between them.

Please help lol.

 

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Sorry forgot some of the question:

Find the energy of the Photon and the Total Energy of the Λ0

 

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Bump?

I'm sure this will take you guys under a minute when compared to the other questions here. I just want an equation or a push in the right direction thanks.