Masses of Open-Flavour Heavy-Light Hybrids from QCD Sum-Rules

TL;DR

This paper predicts the masses of open-flavour heavy-light hybrids using QCD sum-rules, considering various quantum numbers and mixing effects, providing insights into their mass hierarchy and degeneracies.

Contribution

It introduces leading-order QCD sum-rule calculations for heavy-light hybrid masses, including mixing effects with conventional mesons, across multiple quantum states.

Findings

Degeneracy between heavy-nonstrange and heavy-strange hybrids.

Mass hierarchy: 1+ lighter than 1- and 0+ states.

Estimated upper bound on mixing effects increasing hybrid masses.

Abstract

We use QCD Laplace sum-rules to predict masses of open-flavour heavy-light hybrids where one of the hybrid's constituent quarks is a charm or bottom and the other is an up, down, or strange. We compute leading-order, diagonal correlation functions of several hybrid interpolating currents, taking into account QCD condensates up to dimension-six, and extract hybrid mass predictions for all $J^P\in\{0^{\pm},\,1^{\pm}\}$, as well as explore possible mixing effects with conventional quark-antiquark mesons. Within theoretical uncertainties, our results are consistent with a degeneracy between the heavy-nonstrange and heavy-strange hybrids in all $J^P$ channels. We find a similar mass hierarchy of $1^+$, $1^{-}$, and $0^+$ states (a $1^{+}$ state lighter than essentially degenerate $1^{-}$ and $0^{+}$ states) in both the charm and bottom sectors, and discuss an interpretation for the $0^-$ states. If conventional meson mixing is present the effect is an increase in the hybrid mass prediction, and we estimate an upper bound on this effect.