# I D meson decay and invariant mass

1. May 10, 2017

### Narlok

Considering a D0->π+K- where the D meson decays from rest.

If one was to want to calculate the invariant mass of the D meson by measuring the momenta of the pion and kaon, following from conservation of momentum:

m2=(Eπ+EK)2-(pπ+pK)2

However by inputting numerical data
Eπ=137MeV
EK=493MeV
ED=1865MeV

As such, since p2 is some positive quantity it can only reduce the invariant mass, and as the D meson started at rest the invariant mass should be equal to the rest mass:

(137+493)2<<18652

Clearly there is a flaw in my understanding, I'm simply not sure where, and any help would be highly appreciated.

2. May 10, 2017

### Orodruin

Staff Emeritus
These are the masses of the pi and K, not their energies.