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Search for the rare decay Λc+ →pμ+μ-
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The flavor-changing neutral-current (FCNC) decay Λþ c → pμþμ− (inclusion of the charge-conjugate processes is implied throughout) is expected to be heavily suppressed in the Standard Model (SM) by the Glashow-IliopoulosMaiani mechanism [1]. The branching fractions for shortdistance c → ulþl− contributions to the transition are expected to be of Oð10−9Þ in the SM but can be enhanced by effects beyond the SM. However, long-distance contributions proceeding via a tree-level amplitude, with an intermediate meson resonance decaying into a dimuon pair [2,3], can increase the branching fraction up to Oð10−6Þ [4]. The short-distance and hadronic contributions can be separated by splitting the data set into relevant regions of dimuon mass. The Λþ c → pμþμ− decay has been previously searched for by the BABAR Collaboration [5], yielding 11.1 5.0 2.5 events and an upper limit on the branching fraction of 4.4 × 10−5 at 90% C.L. Similar FCNC transitions for the b-quark system (b → slþl−) exhibit a pattern of consistent deviations from the current SM predictions both in branching fractions [6] and angular observables [7], with the combined significance reaching 4 to 5 standard deviations [8,9]. Processes involving c → ulþl− transitions are far less explored at both the experimental and theoretical levels, which makes such measurements desirable. Similar analyses of the D system have reported evidence for the longdistance contribution [10]; however, the short-distance contributions have not been established [11].
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ALFONSO ALBERO, Alejandro, CALVO GOMEZ, M., CAMBONI, Alessandro, COQUEREAU, Samuel, GARRIDO BELTRÁN, Lluís, GASCÓN FORA, David, GRAUGÉS POUS, Eugeni, MARIN BENITO, Carla, LHCb Collaboration. Search for the rare decay Λc+ →pμ+μ-. _Physical Review D_. 2018. Vol. 97, núm. 9, pàgs. 1-10. [consulta: 9 de gener de 2026]. ISSN: 2470-0010. [Disponible a: https://hdl.handle.net/2445/185388]