Observation of a new baryon state in the $Λ^0_bπ^+π^-$ mass spectrum

• Published in: The journal of high energy physics 2020-06, Vol.2020 (6)
• Main Authors: Durham, J. Matthew, Crkovska, Jana, Da Silva, Cesar Luis, Dean, Cameron Thomas, Epple, Eliane Melanie Franziska, Kunde, Gerd Joachim, Li, Xuan, van Hecke, Hubert W.
• Format: Article
• Language: English
• Subjects: ATOMIC AND MOLECULAR PHYSICS; B physics; experiments; Hadron-Hadron scattering; heavy quark production; NUCLEAR PHYSICS AND RADIATION PHYSICS; spectroscopy
• ISSN: 1029-8479; 1029-8479

A new baryon state is observed in the $Λ^0_bπ^+π^-$ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies $\sqrt{s}$ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb-1 . The mass and natural width of the new state are measured to be m = 6072.3 ± 2.9 ± 0.6 ± 0.2 MeV , Γ = 72 ± 11 ± 2 MeV , where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the $Λ^0_b$ baryon mass. The new state is consistent with the first radial excitation of the $Λ^0_b$ baryon, the Λb(2S)0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λb(5912)0 and Λb(5920)0 states are also reported.