# Lattice QCD determination of neutron-antineutron matrix elements with physical quark masses

## TL;DR

This paper presents the first lattice QCD calculations of neutron-antineutron transition matrix elements using physical quark masses, providing crucial data for new physics constraints from experimental searches.

## Contribution

It introduces a detailed lattice QCD methodology for calculating neutron-antineutron matrix elements with physical quark masses, including systematic uncertainty analysis and non-perturbative renormalization.

## Key findings

- Matrix elements are significantly larger than previous MIT bag model estimates.
- Calculations performed with chiral-symmetric discretization and physical quark masses.
- Systematic uncertainties from discretization and finite-volume effects need further study.

## Abstract

Matrix elements of six-quark operators are needed to extract new physics constraints from experimental searches for neutron-antineutron oscillations. This work presents in detail the first lattice quantum chromodynamics calculations of the necessary neutron-antineutron transition matrix elements including calculation methods and discussions of systematic uncertainties. Implications of isospin and chiral symmetry on the matrix elements, power counting in the isospin limit, and renormalization of a chiral basis of six-quark operators are discussed. Calculations are performed with a chiral-symmetric discretization of the quark action and physical light quark masses in order to avoid the need for chiral extrapolation. Non-perturbative renormalization is performed, including a study of lattice cutoff effects. Excited-state effects are studied using two nucleon operators and multiple values of source-sink separation. Results for the dominant matrix elements are found to be significantly larger compared to previous results from the MIT bag model. Future calculations are needed to fully account for systematic uncertainties associated with discretization and finite-volume effects but are not expected to significantly affect this conclusion.