Luminosity in Analysis plot

Hi all,

I know that to identify Luminosity to my N.Events root plot (for any varible like PT), I define it
explicitly through wight : wt = L_data/L_MC = L_data / (sigma/
where L_data is data luminosity and L_MC is MontCarlo luminosity

Right until here ? because when I set sigma = 10^-5 pb, = 10000 and L_data = 200 fb^-1 = 200 * 10^3 pb^-1, wt will be large and it should less than one as I think …

So any one have an idea about these events analysis by root ?