R. Aaij, A. S. W. Abdelmotteleb, Carlos Abellán Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. Aidala, Z. Ajaltouni, S. Akar, K. Carvalho Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, Zakariya Aliouche, P. Álvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis, L. An, L. Anderlini, M. Andersson, A. Andreianov, P. Andreola, M. Andreotti, D. Andreou, Alessia Anelli, D. Ao, F. Archilli, Matteo Argenton, S. Arguedas Cuendis, A. Artamonov, M. Artuso, E. Aslanides, R. Ataíde Da Silva, M. Atzeni, B. Audurier, D. Bacher, I. Bachiller, S. Bachmann, Marie Bachmayer, J. J. Back, P. Baladrón Rodríguez, V. Balagura, A Balboni, W. Baldini, Luca Balzani, H. Bao, J. Baptista de Souza Leite, C. Barbero Pretel, M. Barbetti, I. R. Barbosa, R. J. Barlow, Mikhail Barnyakov, S. Barsuk, W. Barter, Justin Bartz, J. M. Basels, S. Bashir, B. Batsukh, Piera Battista, A. Bay, A. Beck, M. Becker, F. Bedeschi, I. Bediaga, Noah Albin Behling, S. Belin, K. Belous, I. Belov, I. Belyaev, G. Benane, G. Bencivenni, E. Ben-Haim, A. Berezhnoy, R. Bernet, S. Bernet Andres, A. Bertolin, C. Betancourt, F. Betti, J. Bex, Ia. Bezshyiko, O. Bezshyyko, J. Bhom, M. S. Bieker, N. V. Biesuz, P. Billoir, A. Biolchini, M. Birch, F. C. R. Bishop, A. Bitadze, A. Bizzeti, T. Blake, F. Blanc, J. E. Blank
A bstract A search for the doubly-charmed-baryon decay $$ {\Xi}_{cc}^{++}\to {\Xi}_c^0{\pi}^{+}{\pi}^{+} $$ Ξ cc + + → Ξ c 0 π + π + is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 5 . 4 fb − 1 . A significant structure consistent with the $$ {\Xi}_{cc}^{++} $$ Ξ cc + + baryon is observed in the $$ {\Xi}_c^0{\pi}^{+}{\pi}^{+} $$ Ξ c 0 π + π + invariant-mass spectrum. Using the $$ {\Xi}_{cc}^{++}\to {\Lambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+} $$ Ξ cc + + → Λ c + K − π + π + decay as the normalisation channel, the branching fraction ratio, $$ \frac{\mathcal{B}\left({\Xi}_{cc}^{++}\to {\Xi}_c^0{\pi}^{+}{\pi}^{+}\right)}{\mathcal{B}\left({\Xi}_{cc}^{++}\to {\Lambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+}\right)} $$ B Ξ cc + + → Ξ c 0 π + π + B Ξ cc + + → Λ c + K − π + π + , is measured to be 1 . 37 ± 0 . 18 (stat) ± 0 . 09 (syst) ± 0 . 35 (ext). This measurement provides critical input for testing QCD factorisation methods in the weak decays of doubly-heavy baryons, particularly in quantifying nonperturbative effects such as final-state interactions and resonance contributions to the hadronisation process.