TTree::Draw() magic available?

ROOT
1

Hello,

I was wondering if there is any way to solve the following problem with TTree:Draw() et al:

Suppose I have a tree with branches njet and jetpt:

t->Branch("njet", &njet, "njet/i"); t->Branch("jetpt", jetpt, "jetpt[njet]/F");

Is there any way to get to the jet multiplicity njet for a given cut on jetpt, say the number of jets per event with jetpt>10, using TTree::Draw()?

Thanks,
Philipp

2

Hi Philipp,

I think:tree->Draw("njet","njet>10");would do it.

Cheers,
Philippe.

3

Hi Philippe,

I haven’t tried it, but since none of the expressions reference jetpt at all, yet I want to count the jets per event which pass a certain jetpt threshold, I don’t believe it would work this way? Wouldn’t your expression yield the jet multiplicity for events with more than 10 jets?

Cheers,
Philipp

4

Hi Philipp,

Indeed, for ‘the number of jets per event with jetpt>10’, I think you need: tree->Draw("Sum$(jetpt>10)").

Cheers,
Philippe.

5

That does the trick!! I knew TTree::Draw() would come through again … :wink:

Thanks,
Philipp