Observation of a new $\Xi_b^-$ resonance

TL;DR

This paper reports the observation of a new excited $ ext{Xi}_b^-$ baryon resonance at 6227 MeV/c², measured through invariant mass spectra in proton-proton collision data collected by the LHCb experiment, providing insights into bottom baryon spectroscopy.

Contribution

The discovery and detailed measurement of a new $ ext{Xi}_b^-$ resonance, including its mass, width, and decay modes, which advances understanding of bottom baryon states.

Findings

Observation of a new $ ext{Xi}_b^-$ resonance at 6227 MeV/c².

Measured mass and width of the resonance with uncertainties.

Reported relative production rates of decay channels.

Abstract

From samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $\Lambda_b^0K^-$ and $\Xi_b^0\pi^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $\Xi_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $\Xi_b(6227)^-$, the mass and natural width are measured to be $m_{\Xi_{b}(6227)^-}=6226.9\pm2.0\pm0.3\pm0.2$ MeV/$c^2$ and $\Gamma_{\Xi_b(6227)^-}=18.1\pm5.4\pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{\Xi_b(6227)^-}$, is due to the knowledge of the $\Lambda_b^0$ baryon mass. Relative production rates of the ${\Xi_b(6227)^-\to\Lambda_b^0K^-}$ and ${\Xi_b(6227)^-\to\Xi_b^0\pi^-}$ decays are also reported.