# Lifetimes of Doubly Heavy Baryons ${\cal B}_{bb}$ and ${\cal B}_{bc}$

## TL;DR

This paper analyzes the lifetimes of doubly heavy baryons using heavy quark expansion, revealing lifetime hierarchies and the significance of spectator effects, with some subleading corrections challenging the HQE validity.

## Contribution

It provides a detailed theoretical analysis of doubly heavy baryon lifetimes, including spectator effects and subleading corrections, offering new lifetime predictions and hierarchy patterns.

## Key findings

- Lifetime pattern for doubly bottom baryons: $ au( ext{Omega}_{bb}^-) ext{ similar to } au( ext{Xi}_{bb}^-)$
- Significant lifetime differences between $ ext{Xi}_{bc}^+$ and $ ext{Xi}_{bc}^0$ due to spectator effects
- Predicted lifetime ranges for $ ext{Omega}_{bc}^0$, $ ext{Xi}_{bc}^+$, and $ ext{Xi}_{bc}^0$

## Abstract

Lifetimes of the doubly heavy baryons ${\cal B}_{bb}$ and ${\cal B}_{bc}$ are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as $W$-exchange and Pauli interference. For doubly bottom baryons, the lifetime pattern is $\tau(\Omega_{bb}^-)\sim \tau(\Xi_{bb}^{-})>\tau(\Xi_{bb}^0)$. The $\Xi_{bb}^{0}$ baryon is shortest-lived owing to the $W$-exchange contribution, while $\Xi_{bb}^{-}$ and $\Omega_{bb}^{-}$ have similar lifetimes as they both receive contributions from destructive Pauli interference. We find the lifetime ratio $\tau(\Xi_{bb}^{-})/\tau(\Xi_{bb}^0)=1.26$\,. The large $W$-exchange contribution to $\Xi_{bc}^0$ through the subprocess $cd\to us\to cd$ and the sizable destructive Pauli interference contribution to $\Xi_{bc}^+$ imply a substantial lifetime difference between $\Xi_{bc}^+$ and $\Xi_{bc}^0$. In the presence of subleading $1/m_c$ and $1/m_b$ corrections to the spectator effects, we find that $\tau(\Omega_{bc}^0)$ becomes longest-lived. This is because $\Gamma^{\rm int}_+$ and $\Gamma^{\rm semi}$ for $\Omega_{bc}^0$ are subject to large cancellation between dimension-6 and -7 operators. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding that $\Gamma^{cs}_{{\rm int+}}(\Omega_{bc}^0)$, $\Gamma^{{\rm SL},cs}_{\rm int}(\Omega_{bc}^0)$ be positive and $\Gamma^{cu}_{{\rm int-}}(\Xi^+_{bc})$ be negative, we conjecture that $1.68\times 10^{-13}s<\tau(\Omega_{bc}^0)< 3.70\times 10^{-13}s$ , $4.09\times 10^{-13}s<\tau(\Xi_{bc}^+)< 6.07\times 10^{-13}s$ and $0.93\times 10^{-13}s<\tau(\Xi_{bc}^0)< 1.18\times 10^{-13}s$. Hence, the lifetime hierarchy of ${\cal B}_{bc}$ baryons is expected to be the pattern $\tau(\Xi_{bc}^{+})>\tau(\Omega_{bc}^0)>\tau(\Xi_{bc}^0)$.