Constraining New Physics with $h\rightarrow VV$ Tomography

Abstract: The application of quantum information methods to high energy physics has recently been gaining traction. In particular, reconstructing density matrices and measuring entanglement have been investigated for top quark decays and Higgs decays. This paper will further investigate the utility of density matrices for Higgs decays to vector bosons. Imprints of new physics, whether CP-even or CP-odd, in $h \rightarrow VV$ will generally change the spin density matrix, and so the tomographic reconstruction of the density matrix can constrain, or potentially detect, such new physics. New physics, expressed in the language of the Standard Model effective field theory, is analyzed in this framework of quantum tomography. Prospects for $h \rightarrow WW$ are good due to the fully chiral coupling of the $W$ boson to fermions, while $h \rightarrow ZZ$ requires around an order of magnitude more events to reach comparable sensitivity.