Full quantum tomography of top quark decays

Abstract

Quantum tomography in high-energy physics processes has usually been restricted to the spin degrees of freedom. We address the case of top quark decays t→Wb, in which the orbital angular momentum (L) and the spins of W and b are intertwined into a 54-dimensional LWb density operator. The entanglement between L and the W or b spin is large and could be determined for decays of single top quarks produced at the Large Hadron Collider with Run 2 data. With the foreseen statistical and systematic uncertainties, the significance is well above 5σ from the separability hypothesis for L-W entanglement, and 3.2σ for L-b. These would be the first entanglement measurements between orbital and spin angular momenta in high-energy physics. Likewise, the genuine tripartite entanglement between L and the two spins could be established with more than 5σ. The method presented paves the way for similar measurements in other processes.