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arXiv · 1904.00081

Observation of an excited $B_c^+$ state

LHCb collaboration·R. Aaij·C. Abellán Beteta·B. Adeva·M. Adinolfi·C. A. Aidala·Z. Ajaltouni·S. Akar·P. Albicocco·J. Albrecht·F. Alessio·M. Alexander·A. Alfonso Albero·G. Alkhazov·P. Alvarez Cartelle·A. A. Alves Jr·S. Amato·Y. Amhis·L. An·L. Anderlini·G. Andreassi·M. Andreotti·J. E. Andrews·F. Archilli·P. d'Argent·J. Arnau Romeu·A. Artamonov·M. Artuso·K. Arzymatov·E. Aslanides·M. Atzeni·B. Audurier·S. Bachmann·J. J. Back·S. Baker·V. Balagura·W. Baldini·A. Baranov·R. J. Barlow·S. Barsuk·W. Barter·M. Bartolini·F. Baryshnikov·V. Batozskaya·B. Batsukh·A. Battig·V. Battista·A. Bay·F. Bedeschi·I. Bediaga·A. Beiter·L. J. Bel·S. Belin·N. Beliy·V. Bellee·N. Belloli·K. Belous·E. Ben-Haim·G. Bencivenni·S. Benson·S. Beranek·A. Berezhnoy·R. Bernet·D. Berninghoff·E. Bertholet·A. Bertolin·C. Betancourt·F. Betti·M. O. Bettler·M. van Beuzekom·Ia. Bezshyiko·S. Bhasin·J. Bhom·M. S. Bieker·S. Bifani·P. Billoir·A. Birnkraut·A. Bizzeti·M. Bjørn·M. P. Blago·T. Blake·F. Blanc·S. Blusk·D. Bobulska·V. Bocci·O. Boente Garcia·T. Boettcher·A. Bondar·N. Bondar·S. Borghi·M. Borisyak·M. Borsato·M. Boubdir·T. J. V. Bowcock·C. Bozzi·S. Braun·M. Brodski·J. Brodzicka·A. Brossa Gonzalo·D. Brundu
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Abstract

Using $pp$ collision data corresponding to an integrated luminosity of $8.5\,\mathrm{fb}^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of $\sqrt{s} = 7$, $8$ and $13\mathrm{\,Te\kern -0.1em V}$, the observation of an excited $B_c^+$ state in the $B_c^+\pi^+\pi^-$ invariant-mass spectrum is reported. The observed peak has a mass of $6841.2 \pm 0.6 {\,\rm (stat)\,} \pm 0.1 {\,\rm (syst)\,} \pm 0.8\,(B_c^+) \mathrm{\,MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $B_c^+$ mass. It is consistent with expectations of the $B_c^{*}(2^{3}S_{1})^+$ state reconstructed without the low-energy photon from the $B_c^{*}(1^{3}S_{1})^+ \to B_c^+ \gamma$ decay following $B_c^{*}(2^{3}S_{1})^+ \to B_c^{*}(1^{3}S_{1})^+ \pi^+ \pi^-$. A second state is seen with a global (local) statistical significance of $2.2\,\sigma$ ($3.2\,\sigma$) and a mass of $6872.1 \pm 1.3 {\,\rm (stat)\,} \pm 0.1 {\,\rm (syst)\,} \pm 0.8\,(B_c^+) \mathrm{\,MeV}/c^2$, and is consistent with the $B_c(2^{1}S_{0})^+$ state. These mass measurements are the most precise to date.

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LHCb collaboration, R. Aaij, C. Abellán Beteta, B. Adeva, M. Adinolfi, C. A. Aidala, Z. Ajaltouni, S. Akar, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, G. Alkhazov, P. Alvarez Cartelle, A. A. Alves Jr, S. Amato, Y. Amhis, L. An, L. Anderlini, G. Andreassi, M. Andreotti, J. E. Andrews, F. Archilli, P. d'Argent, J. Arnau Romeu, A. Artamonov, M. Artuso, K. Arzymatov, E. Aslanides, M. Atzeni, B. Audurier, S. Bachmann, J. J. Back, S. Baker, V. Balagura, W. Baldini, A. Baranov, R. J. Barlow, S. Barsuk, W. Barter, M. Bartolini, F. Baryshnikov, V. Batozskaya, B. Batsukh, A. Battig, V. Battista, A. Bay, F. Bedeschi, I. Bediaga, A. Beiter, L. J. Bel, S. Belin, N. Beliy, V. Bellee, N. Belloli, K. Belous, E. Ben-Haim, G. Bencivenni, S. Benson, S. Beranek, A. Berezhnoy, R. Bernet, D. Berninghoff, E. Bertholet, A. Bertolin, C. Betancourt, F. Betti, M. O. Bettler, M. van Beuzekom, Ia. Bezshyiko, S. Bhasin, J. Bhom, M. S. Bieker, S. Bifani, P. Billoir, A. Birnkraut, A. Bizzeti, M. Bjørn, M. P. Blago, T. Blake, F. Blanc, S. Blusk, D. Bobulska, V. Bocci, O. Boente Garcia, T. Boettcher, A. Bondar, N. Bondar, S. Borghi, M. Borisyak, M. Borsato, M. Boubdir, T. J. V. Bowcock, C. Bozzi, S. Braun, M. Brodski, J. Brodzicka, A. Brossa Gonzalo, D. Brundu. 2019-03-29. Observation of an excited $B_c^+$ state. https://doi.org/10.1103/physrevlett.122.232001

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