# Special Relativity Decay Q

bon

## Homework Statement

Ok so im given the masses of D meson, pi meson and K meson and told that a D meson at rest decays into a K meson and pi meson. Told to calculate the energy and velocity of the pi meson..

## The Attempt at a Solution

well i know you have to use conservation of 4 momentum..

so energy before = total energy after..and i know that the momenta of the pi and K meson after the collision are equal and opposite, but i cant see how to use this to get total energy of pi meson..:S

any tips?

mgwasser
I remember having this same question, confused me for a while as well.

Your right on the breaking it up into parts:

What is the energy of a D meson at rest? You might have to look this up online, when I solved it this information was supposed to be given (they didn't give the number, we had to look it up).
try using Einsteins Equation

Now After:
What is the rest energy of a K meson and Pi meson? This combined rest energy should be less than the einitial D meson energy. The difference in energy must have been converted to kinetic energy.

M(pi-meson)*V(Pi-Meson) = M(K-meson)*V(K-Meson)

Staff Emeritus
Homework Helper
Do you know four-vectors?

bon
yes :)

what is the four vector method?

thanks

Staff Emeritus