Particle Collision: Calculate Photon Wavelength

[Air]

Homework Statement

The results of particle collisions are observed using particle detectors. Sometimes the products of these collisions are themselves unstable and decay to give further particles; the products of decay can be photons.

In one collision, a stationary \pi^\circ meson is produced which then decays to give two gamma ray photons. The rest mass of the meson is 135 \ MeV/c^2.

\pi ^\circ \rightarrow \beta + \beta​

Calculate the wavelength of each photon.

Homework Equations

E = hf = \frac{hc}{\lambda}

The Attempt at a Solution

How can I find E? I can carry on from that point but I don't know which equation to use to find E?

 

[gendou2]

The energy of the stationary meson is calculated using E = mc²

E_pi = m_pi*c² = 135 MeV / c² * c² = 135 MeV