Seminar held by Paolo Nason "Revisiting the theory of spin correlations and entanglement in top pair production at the LHC"

Recent ATLAS and CMS studies of spin correlations and entanglement in top pair production at hadron colliders have evidenced some inadequacy in the current modeling of the process of top pair production and decay. It has been argued that one needs to include the effect of a very short lived pseudoscalar bound state to reconcile the data with the theoretical prediction. In this talk I review the problem and present an argument that relies upon simple non-relativistic quantum mechanics, that shows that in fact the leading correction due to bound state formation has the same form as other corrections that arise from production in the continuum right above threshold, which reduce the contribution of the bound states by a factor of two. Furthermore, by examining critically the calculation of the process as implemented in current Monte Carlo generators, I show that these corrections, that are of the third subleading order in the strong coupling constant, are tiny, while threshold enhanced corrections of first and second subleading order (not related to bound states) seem to be enough to understand the current discrepancies.