- #1
ck99
- 61
- 0
Homework Statement
Find σ , the differential cross section, starting from the expression below and integrating over solid angle Ω
Homework Equations
dσ/dΩ = r2sin2θ
The Attempt at a Solution
dσ = r2sin2θ dΩ
I remember that dΩ = sinθ dθ dμ
and doing the μ integral from 0 to 2∏ gives dΩ = 2∏ sinθ dθ
substitute into get dσ = 2∏ r2sin2θ sinθ dθ
Now, the next step in the textbook is to substitute u = cos θ and write
σ = 2∏r2∫(1-u2)du with u = cos θ and integration limits from -1 to 1.
I have played around with this step for a while and I know the trig identity sin2 θ = 1 - cos2 θ, but I still don't get how to do this step properly. I think I'm suppose to put a du/dθ term in there, which is a -sinθ term, but I can't see how they get to the final expression in the book, which is
σ = 8∏/3
If anyone can help me work through these steps in detail I would really appreciate it; I should know how to do this by now (4th year physics MSc student!) but it's like my brain switches off every time I see the ∫ symbol and I have to learn everything from scratch every term . . . :(