Search for the doubly charmed baryon Ξcc⁺ in the Ξc⁺ π⁻ π⁺ final state

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A search for the doubly charmed baryon Ξcc⁺ is performed in the Ξc⁺ π⁻ π⁺ invariant-mass spectrum, where the Ξc⁺ baryon is reconstructed in the p K⁻ π⁺ final state. The study uses proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13\,Te -0.1em V, corresponding to a total integrated luminosity of 5.4\,fb⁻¹. No significant signal is observed in the invariant-mass range of 3.4$-$3.8\,Ge -0.1em V/c². Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the Ξcc⁺⁺ → (Ξc⁺ → p K⁻ π⁺) π⁺ decay for different Ξcc⁺ mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25\,Ge -0.1em V/c. The results from this search are combined with a previously published search for the Ξcc⁺ → Λc⁺ K⁻ π⁺ decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620\,Me -0.1em V/c², including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5$-$3.7\,Ge -0.1em V/c² mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.