Search for D* (2007)° → μ+ μ− in B¯ → π−μ+μ− decays

Abstract

[Abstract] The very rare D* (2007)° → μ+μ− decay is searched for by analysing B¯ → π−μ+μ− decays. The analysis uses a sample of beauty mesons produced in proton–proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9fb¯¹. The signal signature corresponds to simultaneous peaks in the μ+μ− and π−μ+μ− invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at B (D* (2007)° → μ+μ−) < 2.6 × 10¯⁸ at 90% confidence level. This is the first limit on the branching fraction of D* (2007)° → μ+μ− decays and the most stringent limit on D* (2007)° decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.