Adding/merging Two 2D histograms

Hi, Is there any way to add/merge two 2D histograms?
I need to add the two histograms generated from some data. I generated two 2D histograms “newdown” and “newup”, which should be added/merged to get a single 2D histogram.

typing the part of a CPP code.

TH2D newdown(“newdown”,“1.0-MR:180.0-thetaCM1”,1000,0,1,1800,0,180);
newdown.SetOption(“COLSCATZ”);
newdown.SetMinimum(1);
tree->Draw("(180.-thetaCM1):(1.-MR)>> newdown",“thetaCM1 > 90. + 74.*(MR-0.5)”," “);
newdown.SetTitle(“1-MR vs 180-thetaCM [Counts];1.0 - Mass Ratio; 180-thetaCM1 [deg]”);
newdown.Write(”",TObject::kOverwrite);

TH2D newup(“newup”,“MR:thetaCM1”,1000,0,1,1800,0,180);
newup.SetOption(“COLSCATZ”);
newup.SetMinimum(1);
tree->Draw(“thetaCM1:MR>>newup”,“thetaCM1 > 90. + 74.*(MR-0.5)”," “);
newup.SetTitle(“MR vs thetaCM [Counts]; Mass Ratio; thetaCM1 [deg]”);
newup.Write(”",TObject::kOverwrite);

Is there any way to merge these two and generate a single 2D histogram (say “new_sum” or some sort of that) out of it?

TH2D new_sum(newdown);
new_sum.SetName(“new_sum”);
new_sum.Add(&newup);