Accessing leaves with RooDataSet

Roofit and RooStats
1

Hi,

I’ve been trying to import a variable from a TTree into a RooDataSet. As far as I understand, it is simple enough to import a TBranch from a TTree, where the branch contains the relevant variable. For a TBranch with the name “Mass” from the TTree “tree” I would do:

RooRealVar mass(“Mass”, “Mass”, 0, 5);
RooDataSet data(“data”, “data”, RooArgSet(mass), Import(*tree));

However, how do I import a leaf from a branch? What if I have a branch “Child1” with the leaf “Mass”? The following does not work (as I would expect it to):

RooRealVar mass(“Child1.Mass”, “Child1.Mass”, 0, 5);
RooDataSet data(“data”, “data”, RooArgSet(mass), Import(*tree));

Is this even possible to do, or can only branches be imported as variables? Thanks for any pointers on this.

2

Hello,

if all the variables you want to import are part of the same branch in the tree I believe you can use:

TTree* tree = (TTree*) file.Get(“tree/Child1”);

and then import “Mass”. If you want to import also other variables from other branches: you can import the variables of Child1 in a dataset1 and Child2 in dataset2 and then merge the datasets (if that’s what you want to do).

You can also create an empty dataset:

RooRealVar mass(“Mass”, “Mass”, 0, 5);
RooArgSet row(mass);
RooDataSet data(“data”, “data”, row);

and then loop over the tree(s) entries and add each row one by one with in the loop:

mass->setVal(…);
data.add(row);

Regards,

– Gregory