# Homework Help: Cross-section Normalisation

1. Jul 29, 2011

### v0id19

Just a quick question--long story short, I need to normalise a plot by the cross-section, but I'm not sure how to do that and the Google hasn't been too helpful.
I was thinking about scaling it by the cross-section times the luminosity--does this sound reasonable?

2. Jul 29, 2011

### Mike Pemulis

Just so I have this straight -- you have a histogram in some parameter x (where x is some scattering angle or energy or something), so that the total area under the curve is the total number of events. You would like the total area under the curve to be the (total) cross-section. Is that right?

In that case, you would just divide by the luminosity, not the luminosity times the cross section. The reason is that, assuming perfect efficiency and so on, we have,

N = sigma*L

where N is the number of events, sigma is the cross-section, and L is the luminosity. Scaling the curve by sigma*L would therefore scale it by N, which would normalize your histogram to unity. If instead you want to normalize it to sigma, just divide by L.

I hope that makes sense and is what you are looking for.