Compare two histogram

Hey everybody
I have two histograms of the same variable from different sources (detectors). That is, The first is, pT variable measurement from detector1, I call it pT1 in atree. The second is the same pT measurement from detector2, I call it pT2 in the same tree.
I noticed, in each pT bin, detector1 has more counts than detector2. Which tells me detector2 is less efficient than detector1. I want to find the efficiency of detector2 as compared with detector1 (as ideal detector) as a function of pT.
How can I do that?
Thank you for your time.

You can make the two histograms from the tree and make the difference of this two histograms.