Search for the doubly charmed baryon Ξ+cc in the Ξ+cπ−π+ final state

Abstract

A search for the doubly charmed baryon Ξ+ cc is performed in the Ξ+ c π −π + invariant-mass spectrum, where the Ξ+ c baryon is reconstructed in the pK−π + final state. The study uses proton-proton collision data collected with the LHCb detector at a centreof-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb−1 . No significant signal is observed in the invariant-mass range of 3.4-3.8 GeV/c 2 . Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the Ξ++ cc → (Ξ+ c → pK−π +)π + decay for different Ξ+ cc mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the Ξ+ cc → Λ + c K−π + decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c 2 , including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5-3.7 GeV/c 2 mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.