Comerma Montells, AlbertGarcia Moreno, PaulaGarrido Beltrán, LluísGioventù, AlessandraGironella Gironell, PereGomez Fernandez, SergioGraugés Pous, EugeniLobo Salvia, AniolLópez Huertas, AlbertManera Escalero, RafelMarin Benito, CarlaMauricio Ferre, JoanCalefice, LukasVazquez Gomez, RicardoLHCb Collaboration2025-06-272025-06-2720241126-6708https://hdl.handle.net/2445/221850The frst observation of the B+ c → J/ψπ+π 0 decay is reported with high signifcance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1 , collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the B+ c → J/ψπ+ channel is measured to be BB + c →J/ψπ+π0 BB + c →J/ψπ+ = 2.80 ± 0.15 ± 0.11 ± 0.16 , where the frst uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B+ → J/ψK∗+ and B+ c → J/ψπ+ decays, which are used to determine the π 0 detection efciency. The π +π 0 mass spectrum is found to be consistent with the dominance of an intermediate ρ + contribution in accordance with a model based on QCD factorisation. 28 p.application/pdfengcc-by (c) Aaij, R. et al., 2024http://creativecommons.org/licenses/by/4.0/Gran Col·lisionador d'HadronsHadronsCromodinàmica quànticaLarge Hadron Collider (France and Switzerland)HadronsQuantum chromodynamicsinfo:eu-repo/semantics/article7564692025-06-27info:eu-repo/semantics/openAccess