Search for the doubly charmed baryon Ξ_cc⁺ in the Ξ_c⁺π⁻π⁺ final state

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 centre- of-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/c². 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/c², including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/c² mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.