# Observation of new resonances in the $\Lambda_{b}^0\pi^+\pi^-$ system

## TL;DR

This paper reports the discovery of two new narrow excited states in the $\Lambda_b^0 ext{-}\pi^+ ext{-}\pi^-$ spectrum, measured with high precision, and interprets them as a doublet of $\Lambda_b ext{(1D)}^0$ states.

## Contribution

It provides the first observation and precise measurements of two nearly degenerate $\Lambda_b$ excited states, suggesting their identification as a $\Lambda_b ext{(1D)}^0$ doublet.

## Key findings

- Two new $\Lambda_b$ excited states observed with masses around 6146 and 6152 MeV.
- Mass splitting between the states measured to be approximately 6.34 MeV.
- States are consistent with a $\Lambda_b ext{(1D)}^0$ doublet interpretation.

## Abstract

We report the observation of a new structure in the $\Lambda_b^0 \pi^+\pi^-$ spectrum using the full LHCb data set of $pp$ collisions, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$, collected at $\sqrt{s}=7$, 8 and $13\,\mathrm{TeV}$. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be \begin{eqnarray*} m_{\Lambda_{b}\mathrm{(6146)}^0} &=&6146.17 \pm 0.33 \pm 0.22 \pm 0.16\,\mathrm{MeV} \,, m_{\Lambda_{b}\mathrm{(6152)}^0} &=&6152.51 \pm 0.26 \pm 0.22 \pm 0.16\,\mathrm{MeV} \,, \Gamma_{\Lambda_{b}\mathrm{(6146)}^0}&=&\phantom{615}2.9\phantom{0}\pm 1.3\phantom{0} \pm 0.3\phantom{0}\,\mathrm{MeV}\,, \Gamma_{\Lambda_{b}\mathrm{(6152)}^0} &=&\phantom{615}2.1\phantom{0}\pm 0.8\phantom{0} \pm 0.3\phantom{0}\,\mathrm{MeV}\,, \end{eqnarray*} with a mass splitting of $\Delta m = 6.34 \pm 0.32 \pm 0.02\,\mathrm{MeV}$, where the first uncertainty is statistical, the second systematic and the third derives from the knowledge of the mass of the $\Lambda_b^0$ baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of $\Lambda_{b}\mathrm{(1D)}^0$ states.