Observation of New Resonances in the Λb0 π+π- System

Abstract

We report the observation of a new structure in the Λ0 bπþπ− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9 fb−1, collected at ffiffi s p ¼ 7, 8, and 13 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 mΛbð6146Þ0 ¼ 6146.17 0.33 0.22 0.16 MeV; mΛbð6152Þ0 ¼ 6152.51 0.26 0.22 0.16 MeV; ΓΛbð6146Þ0 ¼ 2.9 1.3 0.3 MeV; ΓΛbð6152Þ0 ¼ 2.1 0.8 0.3 MeV;with a mass splitting of Δm ¼ 6.34 0.32 0.02 MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λ0 b baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λbð1DÞ0 states.