Constraining New Physics with $h\rightarrow VV$ Tomography

TL;DR

This paper explores how quantum tomography of Higgs decays to vector bosons can detect or constrain new physics effects, including CP violation, by analyzing changes in the spin density matrix.

Contribution

It introduces a novel approach using quantum tomography to analyze Higgs decay data for signs of new physics within the Standard Model effective field theory.

Findings

Tomographic reconstruction can constrain CP-even and CP-odd new physics effects.

Good prospects for $h ightarrow WW$ due to chiral couplings.

Higher event counts needed for $h ightarrow ZZ$ sensitivity.

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.