It’s a similar problem to this
A workaround: add an empty subscript to the opening parenthesis:
{
auto c1 = new TCanvas("c1","Examples of TGaxis",10,10,700,500);
c1->Range(-10,-1,10,1);
auto axis1 = new TGaxis(-4.5,-0.2,5.5,-0.2,-6,8,510,"");
axis1->SetTitle("(d_{0}^{reco} - d_{0}^{true})/#sigma");
axis1->Draw();
auto axis2 = new TGaxis(-4.5,0.4,5.5,0.4,-6,8,510,"");
axis2->SetTitle("(_{}d_{0}^{reco} - d_{0}^{true})/#sigma");
axis2->Draw();
}
