Prof. Dr. Herbert Dreiner

There has recently been a surge of interest in tests of locality via Bell’s inequality at the LHC, in particular in the $t\bar t$ system. Atlas and CMS have also claimed to test for entanglement versus non-entanglement. We argue that neither of these possibilities are valid. The reasons are quite fundamental, as inherently only commuting observables are measured at the LHC (momenta). An underlying problem is that the entanglement is typically expressed in terms of a spin correlation matrix, which can not be measured. Instead the angular correlation matrix of the outgoing momenta is measured. We prove that deriving the former from the latter necessarily always involves assuming quantum mechanics. Thus one can not use this as a fundamental test of quantum mechanics.