#include <iostream>
#include <fstream>
#include <TFile.h>
#include <TTree.h>

void UpdateBranch(const char* filename, const char* treename, Double_t a, Double_t b) {
    TFile *file = new TFile(filename, "UPDATE");
    TTree *data = (TTree*)file->Get(treename);


    // Create new branch for the updated energy values
    Double_t energy_updated1; // Updated energy values
    Double_t energy; // energy values

    data->SetBranchAddress("detector.energy", &energy);
    TBranch *newBranch = data->Branch("energy_updated1", &energy_updated1, "energy_updated1/D");

    Int_t nEntries = data->GetEntries();

    for (Int_t entry = 0; entry < nEntries; entry++) {
        data->GetEntry(entry);
        energy_updated1 = a + b * energy; // Apply the calibration
        newBranch->Fill();
    }

    // Write the new branch back to the tree
    data->Write("", TObject::kOverwrite);

    file->Close();
}