Filling a tree with an object array

ROOT
1

Hi,
I am trying to fill a branch of a root tree with an array of TLorentzVectors, but I do not know how to do this correctly. I have tried the following code, wich seemed like the obvious way to do it to me:

TFile hfile = (TFile)gROOT->FindObject(“MCdata.root”);
if (hfile)
hfile->Close();
hfile = new TFile(“MCData.root”,“RECREATE”);
Int_t split = 0;
Int_t bsize = 64000;
TTree *MCTree = new TTree(“MCTree”,"");

TLorentzVector *bhiggs[2];

MCTree->Branch(“bhiggs”,“TLorentzVector”,&bhiggs,bsize,split);

but i get a segmentation violation. I would like to use a TClonesArray, but I dont think they work with TLorentzVectors. Is this the case, and do you have any other ideas for how to do this?
Thanks,
Clare

2

You must correctly preset the pointer before calling TTree::Branch. eg:

[code]{
TFile *hfile = new TFile(“MCData.root”,“RECREATE”);
Int_t split = 0;
Int_t bsize = 64000;
TTree *MCTree = new TTree(“MCTree”,"");

TLorentzVector *bhiggs[2] ={0,0};

MCTree->Branch(“bhiggs0”,“TLorentzVector”,&bhiggs[0],bsize,split);
MCTree->Branch(“bhiggs1”,“TLorentzVector”,&bhiggs[1],bsize,split);
MCTree->Print();
}
[/code]

Rene

3

Thanks for replying so quickly.

That stops the segmentation violation when the branch is declared. However, if I then try and access the elements of the array like this:

TLorentzVector *bhiggs[2] ={0,0};

MCTree->Branch(“bhiggs0”,“TLorentzVector”,&bhiggs[0],bsize,split);
MCTree->Branch(“bhiggs1”,“TLorentzVector”,&bhiggs[1],bsize,split);
bhiggs[0]->SetPxPyPzE(0,0,0,0)

I get the error:

Error: illegal pointer to class object bhiggs[0] 0x0 987

Do I need to access the elements in a different way?

Thanks,
Clare

4

You get this error because you call SetPxPyPzE with a null pointer.
You must create the TLorentzVector objects first.

Rene