The neutral pion (0) is an unstable particle produced in high-energy particle collisions. Its mass is about

The neutral pion (π0) is an unstable particle produced in high-energy particle collisions. Its mass is about 264 times that of the electron, and it exists for an average lifetime of 8.4 x 10-17 s before decaying into two gamma-ray photons. Using the relationship E = mc2 between rest mass and energy, find the uncertainty in the mass of the particle and express it as a fraction of the mass.