Observation of the $\Lambda_b^0\rightarrow J/\psi p \pi^-$ decay

R. Aaij , Y. Amhis (1) , S. Barsuk (1) , M. Borsato (1) , O. Callot (1) , O. Kochebina (1) , J. Lefrançois (1) , F. Machefert (1) , A. Martin Sanchez (1) , M. Nicol (1) , P. Robbe (1) , M.-H. Schune (1) , M. Teklishyn (1) , A. Vallier (1) , B. Viaud (1) , E. Ben-Haim (2) , M. Benayoun (2) , P. David (2) , L. del Buono (2) , A. Martens (2) , D.A. Milanes (2) , F. Polci (2) , Ziad Zj Ajaltouni (3) , M. Baalouch (3) , E. Cogneras (3) , O. Deschamps (3) , I. El Rifai (3) , M. Grabalosa Gándara (3) , Pierre Henrard (3) , M. Hoballah (3) , R. Lefèvre (3) , J. Maratas (3) , S. Monteil (3) , V. Niess (3) , Pascal Perret (3) , Diego Alejandro Roa Romero (3) , L. Beaucourt (4) , D. Decamp (4) , N. Déléage (4) , Ph. Ghez (4) , J.-P. Lees (4) , J.F. Marchand (4) , M.-N. Minard (4) , B. Pietrzyk (4) , W. Qian (4) , S. t'Jampens (4) , V. Tisserand (4) , E. Tournefier (4) , S. Akar (5) , E. Aslanides (5) , J. Cogan (5) , W. Kanso (5) , R. Legac (5) , O. Leroy (5) , G. Mancinelli (5) , A. Mordà (5, 6) , M. Perrin-Terrin (5) , J. Serrano (5) , A. Tsaregorodtsev (5)

1 LAL - Laboratoire de l'Accélérateur Linéaire
2 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
3 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
4 LAPP - Laboratoire d'Annecy de Physique des Particules
5 CPPM - Centre de Physique des Particules de Marseille
6 CPT - Centre de Physique Théorique - UMR 7332

The first observation of the Cabibbo-suppressed decay $\Lambda_b^0\rightarrow J/\psi p \pi^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $\Lambda_b^0\rightarrow J/\psi p K^-$ is determined to be $$ \frac{{\cal B}(\Lambda_b^0\rightarrow J/\psi p \pi^-)}{{\cal B}(\Lambda_b^0\rightarrow J/\psi p K^-)}=0.0824\pm0.0025\:(\text{stat})\pm0.0042\:(\text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p \pi^-)-{\cal A}_{CP}(\Lambda_b^0\rightarrow J/\psi p K^-)=(+5.7\pm 2.3\:(\text{stat})\pm1.2\:(\text{syst}))\%, $$ which is compatible with CP symmetry at the $2.2\sigma$ level.

Domaines: Physique des Hautes Energies - Expérience [hep-ex]

R. Aaij, Y. Amhis, S. Barsuk, M. Borsato, O. Callot, et al.. Observation of the $\Lambda_b^0\rightarrow J/\psi p \pi^-$ decay. Journal of High Energy Physics, 2014, 7, pp.103. ⟨10.1007/JHEP07(2014)103⟩. ⟨in2p3-00999792⟩