The strangest lifetime: A bizarre story of $\tau(\Omega_c^0)$

TL;DR

The paper reviews the unexpected increase in the measured lifetime of the $\,Omega_c^0$ baryon, discusses the failure of heavy quark expansion to explain this, and suggests a longer lifetime than previously thought.

Contribution

It highlights the discrepancy between experimental measurements and theoretical predictions of $\,Omega_c^0$ lifetime, emphasizing the limitations of heavy quark expansion at higher orders.

Findings

LHCb measurements significantly increased the $\,Omega_c^0$ lifetime estimate.

Heavy quark expansion fails at order $1/m_c^4$ for $\,Omega_c^0$.

A sensible HQE implies $\,Omega_c^0$ lifetime exceeds that of $\,\,Lambda_c^+$.

Abstract

For a long time it has been established both experimentally and theoretically that $\Omega_c^0$ is shortest-lived among the four singly charmed baryons which decay weakly. The situation was dramatically changed in 2018 when LHCb reported a new measurement of the $\Omega_c^0$ lifetime using semileptonic $b$-hadron decays. The value is nearly four times larger than the previous world average of $\tau(\Omega_c^0)$ and it is confirmed by the most recent LHCb measurement with the prompt production. In this viewpoint article, we review the status and point out that heavy quark expansion (HQE) fails to apply to $\Omega_c^0$ to the order of $1/m_c^4$. By demanding a sensible HQE for $\Omega_c^0$ will lead to a lifetime of $\Omega_c^0$ longer than $\Lambda_c^+$.