Quantum tomography at colliders: With or without decays

In constructing quantum states at colliders, most efforts have focused on utilizing the particle decays to infer the spins to reconstruct the quantum density matrix. We show that the production kinematics of the particles provides sufficient information about the spins to establish quantum tomography event-by-event without using the decays. We lay out the advantages of using this “kinematic approach” relative to the usual “decay approach.” Since the kinematic approach leverages the simplicity of scattering kinematics, this approach promises to achieve optimal statistical results for quantum tomography at colliders.