Observation of photon polarization in the $b \to s\gamma$ transition

R. Aaij , Y. Amhis (1) , S. Barsuk (1) , O. Callot (1) , J. He (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) , I. de Bonis (4) , D. Decamp (4) , N. Déléage (4) , Ph. Ghez (4) , J.-P. Lees (4) , M.-N. Minard (4) , B. Pietrzyk (4) , W. Qian (4) , S. t'Jampens (4) , V. Tisserand (4) , E. Tournefier (4) , 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) , M. Sapunov (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

This Letter presents a study of the flavor-changing neutral current radiative $B^{\pm} \to K^{\pm}\pi^{\mp}\pi^{\pm}\gamma$ decays performed using data collected in proton-proton collisions with the LHCb detector at $7$ and $8\,$TeV center-of-mass energies. In this sample, corresponding to an integrated luminosity of $3\,\text{fb}^{-1}$, nearly $14\,000$ signal events are reconstructed and selected, containing all possible intermediate resonances with a $K^{\pm}\pi^{\mp}\pi^{\pm}$ final state in the $[1.1, 1.9]\,$GeV/$c^{2}$ mass range. The distribution of the angle of the photon direction with respect to the plane defined by the final-state hadrons in their rest frame is studied in intervals of $K^{\pm}\pi^{\mp}\pi^{\pm}$ mass and the asymmetry between the number of signal events found on each side of the plane is obtained. The first direct observation of the photon polarization in the $b \to s\gamma$ transition is reported with a significance of $5.2\,\sigma$.

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

R. Aaij, Y. Amhis, S. Barsuk, O. Callot, J. He, et al.. Observation of photon polarization in the $b \to s\gamma$ transition. Physical Review Letters, 2014, 112, pp.161801. ⟨10.1103/PhysRevLett.112.161801⟩. ⟨in2p3-00953255⟩