# Units in Particle Physics

#### ylem

Hello!

I was wondering if someone could help me with a problem of units!

I'm currently deriving probability equations for neutrino oscillations and I'm stuck with units!

I have: [(mass)^2 * time]/[4*energy] and I want to write it as [1.27 * (mass)^2 * distance]/[Energy] with distance in metres, energy in MeV and the mass in eV^2. I get that I can use the relativist approximation to get from time to distance (taking c and hbar to be 1).

I'm just wondering how you get the 1.27 that allows you to use this conversion? I assume it is [1eV^2 * 1 metre in MeV * (1/MeV)] but I don't know what 1 metre is in MeV. Can someone explain to how determine it?

Also, if anyone could explain how to get seconds in inverse MeV that would be great!

Thanks a lot, Sam

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#### clem

There is a conversion 1=197 MeV-fm.
(you get that from 1=hbar*c.)
Then use 1=3X10^8 m/s.

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