Search for excited B_c⁺ states

A search is performed in the invariant mass spectrum of the B _c ⁺ π⁺π⁻ system for the excited B _c ⁺ states B _c (2¹S₀)⁺ and B _c (2³S₁)⁺ using a data sample of pp collisions collected by the LHCb experiment at the centre-of-mass energy of s√=8 TeV, corresponding to an integrated luminosity of 2 fb⁻¹. No evidence is seen for either state. Upper limits on the ratios of the production cross-sections of the B _c (2¹S₀)⁺ and B _c (2³S₁)⁺ states times the branching fractions of B _c (2¹S₀)⁺ → B _c ⁺ π⁺π⁻ and B _c (2³S₁)⁺ → B _c ^{* +}π⁺π⁻ over the production cross-section of the B _c ⁺ state are given as a function of their masses. They are found to be between 0.02 and 0.14 at 95% confidence level for B _c (2¹S₀)⁺ and B _c (2³S₁)⁺ in the mass ranges [6830, 6890] MeV/c² and [6795, 6890] MeV/c², respectively.