Hey, Im just woondering if anyone here have computed (numerically) the Breit-Wigner for a particle decay. I have to do some nonlinear fitting of data but I need to compute this, any ideas? My case is specific, and Im brand new to particle physics, it's for a tau decay into Kaon, pion and tau neutrino. The expression I have for the Breit-Wigner is posted in: http://mathbin.net/5566 [Broken] I still dont understand the math beneath the expression. All Im asked is to compute it, what Im having trouble with is that i on the Breit-Wigner, im not sure if thats the imaginary unit or something different, so if you know please help me compute this. Thanks for the attention.