Observation of New Resonances in the Λ_{b}^{0}π^{+}π^{-} System

Area of Science:

• High Energy Physics
• Particle Physics
• Hadron Spectroscopy

Background:

• The Lambda b0 (Λ_{b}^{0}) baryon is a key system for studying the strong interaction.
• Understanding excited states of baryons provides insights into quark dynamics and quantum chromodynamics (QCD).
• Previous studies have explored the spectroscopy of bottom baryons, but the existence of certain excited states remains under investigation.

Purpose of the Study:

• To search for and characterize new excited states of the Lambda b0 (Λ_{b}^{0}) baryon.
• To precisely measure the masses and widths of any newly observed states.
• To interpret the observed structures in the context of theoretical models of baryon excitation.

Main Methods:

• Analysis of the Λ_{b}^{0}π^{+}π^{-} invariant mass spectrum using the full LHCb data set.
• Data collected from proton-proton (pp) collisions at center-of-mass energies of 7, 8, and 13 TeV.
• Statistical and systematic uncertainty evaluation, including contributions from the Λ_{b}^{0} mass determination.

Main Results:

• Observation of a significant new structure in the Λ_{b}^{0}π^{+}π^{-} spectrum.
• The structure is interpreted as a superposition of two narrow, nearly degenerate states.
• Precise measurements of the masses and widths of these two states, denoted as Λ_{b}(6146)^{0} and Λ_{b}(6152)^{0}, with a small mass splitting.
• The measured properties are consistent with a doublet of Λ_{b}(1D)^{0} states.

Conclusions:

• The discovery of these two new excited Λ_{b}^{0} states provides crucial data for understanding baryon spectroscopy.
• The interpretation as Λ_{b}(1D)^{0} states offers valuable constraints for theoretical models of heavy quark systems.
• This finding contributes to the ongoing exploration of the complex spectrum of bottom baryons.