Observation of a new baryon state in the Λb0π+π−$$ {\Lambda}_{\mathrm{b}}^0{\pi}^{+}{\pi}^{-} $$ mass spectrum

Abstract

Abstract

A new baryon state is observed in the Λb0π+π−$$ {\Lambda}_{\mathrm{b}}^0{\pi}^{+}{\pi}^{-} $$ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies s$$ \sqrt{s} $$ = 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 ,

$$ {\displaystyle \begin{array}{l}m=6072.3\pm 2.9\pm 0.6\pm 0.2\ \mathrm{MeV},\\ {}\Gamma =72\pm 11\pm 2\ \mathrm{MeV},\end{array}} $$

where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Λb0$$ {\Lambda}_{\mathrm{b}}^0 $$ baryon mass. The new state is consistent with the first radial excitation of the Λb0$$ {\Lambda}_{\mathrm{b}}^0 $$ 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.