Partial decay width in Mathematica

1. Feb 20, 2015

Safinaz

Hi there,

I have a a partial decay width in form of $\frac{d \Gamma}{d \cos{\theta}~ dq^2} =$ some terms functions in q and $\theta$ variables.
How to integrate this decay width in Mathematica over this two variables ?

I tried some thing like
j[q_]:= $\int_{1}^{-1}$ Gam[q, $\theta$] d Cos[$\theta$]

then

$\int_{0}^{10}$ j[q] dq^2

But it gave me errors

Cos[$\theta$] is not a valid variable.
Integrate::ilim: Invalid integration variable or limit(s) in {q^2,0,10}. >>

I also tried to use NIntegrate..

So any help in that ?

Cheers,
S.

2. Feb 20, 2015

Staff: Mentor

$d \cos(\theta) = - \sin(\theta) d\theta$ should help (don't forget the integration limits). Alternatively, express everything in terms of $\cos(\theta)$ and give this a new name.