Observation of five new narrow $Ω_c^0$ states decaying to $Ξ_c^+ K^-$

Abstract: The $\Xi_c^+ K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb$^{-1}$, collected by the LHCb experiment. The $\Xi_c^+$ is reconstructed in the decay mode $p K^- \pi^+$. Five new, narrow excited $\Omega_c^0$ states are observed: the $\Omega_c(3000)^0$, $\Omega_c(3050)^0$, $\Omega_c(3066)^0$, $\Omega_c(3090)^0$, and $\Omega_c(3119)^0$. Measurements of their masses and widths are reported.

• The paper reports the discovery of five new narrow Omega_c⁰ states with high statistical significance in proton-proton collisions.
• It employs detailed analysis of the Ξ_c⁺ K⁻ decay mode to accurately measure the resonances' masses and widths.
• These findings provide experimental insights that refine theoretical models in heavy baryon spectroscopy and Quantum Chromodynamics.

Observation of Five New Narrow $\Omegac$ States

The LHCb collaboration's study, published in Physical Review Letters, reports the discovery of five new narrow excited states of the $\Omegac$ baryon. The investigation capitalized on proton-proton collision data with an integrated luminosity of 3.3 fb$^{-1}$ collected by the LHCb experiment at the Large Hadron Collider (LHC). The $\Omegac$ baryon, with quark content $c s s$, highlights the complex mass spectrum of singly charmed baryons, acting as a pertinent test of contemporary theoretical models, including heavy quark effective theory (HQET) and diquark models.

The study investigated the mass spectrum of the decay mode $\Xi^+_c K^-$, exploiting the capability of the LHCb detector to reconstruct charm baryons like $\Xi_c$. This work documents the resonances $\Omegac(3000)^0$, $\Omegac(3050)^0$, $\Omegac(3066)^0$, $\Omegac(3090)^0$, and $\Omegac(3119)^0$. The masses and widths of these states were measured with high precision, the significance of their detection is especially notable: 20.4 $\sigma$, 20.4 $\sigma$, 23.9 $\sigma$, 21.1 $\sigma$, and 10.4 $\sigma$ respectively.

The experimental results present these five $\Omegac$ states as narrow peaks in the invariant mass distribution of the $\Xi^+_c K^-$ system, suggesting bound states or resonances. The lack of significant structures in control samples like the wrong-sign $\Xi^-_c K^+$ combinations confirms the resonant nature of the narrow peaks. Moreover, a broad structure around 3188 MeV/$c^2$ is noted in the spectrum, which was fitted as a single additional resonance in this analysis.

The unexpected outcomes in this study provide rich data to confront theoretical models. The $\Omegac$ system is particularly sensitive to the dynamics predicted by HQET due to its unique content of heavy and strange quarks. These results offer new insight into the interaction between the charm quark and strange quark pair in the weak baryon decay process, posing challenges to hadron physics theorists, especially in terms of calculating the spectrum of states in Quantum Chromodynamics (QCD).

The implications for heavy-baryon spectroscopy are considerable. Future work may involve determining the spin-parity assignments of these states, possibly through angular correlation studies in other decay modes accessible to current or future experimental setups. Implementing Lattice QCD and other theoretical methods on these measurement results might refine the existing frameworks or even propose novel corrections or extensions. Additionally, further experimental studies will help probe for additional states, resolve the nature of the broad structure, and refine the understanding of charmed baryon interactions within the complex QCD regime.

In sum, the observation of these $\Omegac$ states not only enriches the $\cquark\squark\squark$ baryon spectrum but also underscores the potential for discovery and deeper understanding through the vast datasets enabled by detectors at facilities like the LHC.