TLorentzVector p1(50, 0, 0, 50); cout << p1.Phi() << endl;
1.5708
TLorentzVector p2(50, 30, 0, 40); cout << p2.Phi() << endl;
0.643501This example creates a TLorentzVector with energy 50 GeV, momentum of 30 GeV in the x direction and 40 GeV in the z direction. The Phi method returns the azimuthal angle of the vector in radians, which is approximately 0.64. Package/Library: The TLorentzVector class is part of the ROOT framework, specifically the ROOT Math Core library.