We present a study of the CP asymmetry in the B⁰ → D*+D*- decay, using data produced by the electron-positron asymmetric-energy accelerator KEKB (Tsukuba, Japan) running at the Υ(4S) resonance. We use the full data sample (as of summer 2008) of 657 × 106BB events, which corresponds to an integrated luminosity of 605 fb-1 recorded with the Belle detector. From the distributions of the proper-time intervals between a neutral B meson decay to the D*+D*- final state and another flavor-tagged B⁰ or B⁰ decay, we measure the CP-violation parameters A and S. A is a measure of the direct CP violation in the decay amplitudes while a non-zero S value indicates CP violation in the interference between the decay and the mixing amplitudes. At the quark level the B⁰ → D*+D*- decay is a b → ccd transition, where the tree amplitude is Cabbibo-suppressed. The contribution of penguin amplitudes in this decay is estimated to be at the percent level [1]. When ignoring penguin corrections, the SM prediction for the CP parameters are AD*+D*- = 0 and SD*+D*- = -ηD*+D*- sin 2β, where ηD*+D*- is the CP eigenvalue of D*+D*- and β = arg[-VcdVcb]/[VtdVtb] is an observable phase related to the coefficients Vij of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. Any large measured deviation with respect to prediction can be a sign of New Physics. As the D* particle is a vector-meson three different partial waves contribute to the final states: the S and D correspond to the CP-even state, while the P wave corresponds to a CP-odd state. To avoid too large a dilution of the CP asymmetry, the two CP components should be separated on a statistical basis. We measure the CP-odd fraction by performing a time-integrated angular analysis in the transversity basis and obtain: R⊥ = 0.125 ± 0.043(stat) ± 0.023(syst). which is consistent with the prediction from theory as well as the previous measurements. We have taken into account the CP-odd dilution and the effect of incorrect flavor assignment to model the decay rates. The proper-time difference of the two B mesons is obtained using the reconstructed D-meson trajectories and the beam spot profile. A "null" measurement is performed by fitting the CP asymmetry of the control sample, B⁰ → D()+Ds()- which gives A = -0.02 ± 0.03(stat) and S = -0.07 ± 0.04(stat) and is consistent with no CP violation. The lifetime fit to the B⁰ → D*+D*- is used to verify the precision of the vertex resolution function. The measured lifetime is consistent with the world average value. Finally, the CP study of the B⁰ → D*+D*- decay gives an evidence of CP violation with a 3.5 σ significance: where S'D*+D*- = 1/η SD*+D*-. This result is consistent with the SM prediction for tree decays.
Jian Wang, Olivier Schneider, Yiming Li, Yi Zhang, Aurelio Bay, Guido Haefeli, Christoph Frei, Frédéric Blanc, Tatsuya Nakada, Michel De Cian, Luca Pescatore, François Fleuret, Elena Graverini, Chitsanu Khurewathanakul, Renato Quagliani, Maria Vieites Diaz, Federico Betti, Aravindhan Venkateswaran, Luis Miguel Garcia Martin, Vitalii Lisovskyi, Sebastian Schulte, Veronica Sølund Kirsebom, Mingkui Wang, Zhirui Xu, Lei Zhang, Jessica Prisciandaro, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Marc-Olivier Bettler, Greig Alan Cowan, Maurizio Martinelli, Vladislav Balagura, Donal Patrick Hill, Liang Sun, Pietro Marino, Mirco Dorigo, Xiaoxue Han, Liupan An, Federico Leo Redi, Plamen Hristov Hopchev, Thibaud Humair, Maxime Schubiger, Hang Yin, Guido Andreassi, Violaine Bellée, Olivier Göran Girard, Axel Kuonen, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Evgenii Shmanin, Dipanwita Dutta, Zheng Wang, Yi Wang, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Giovanni Carboni, Victor Coco, Adam Davis, Paolo Durante, Wenyu Zhang, Yu Zheng, Anton Petrov, Maxim Borisyak, Feng Jiang, Zhipeng Tang
Jian Wang, Olivier Schneider, Yiming Li, Yi Zhang, Aurelio Bay, Guido Haefeli, Christoph Frei, Frédéric Blanc, Tatsuya Nakada, Michel De Cian, Luca Pescatore, François Fleuret, Elena Graverini, Chitsanu Khurewathanakul, Renato Quagliani, Maria Vieites Diaz, Federico Betti, Aravindhan Venkateswaran, Luis Miguel Garcia Martin, Vitalii Lisovskyi, Katharina Müller, Sebastian Schulte, Veronica Sølund Kirsebom, Mingkui Wang, Zhirui Xu, Lei Zhang, Ho Ling Li, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Marc-Olivier Bettler, Greig Alan Cowan, Maurizio Martinelli, Vladislav Balagura, Donal Patrick Hill, Liang Sun, Pietro Marino, Mirco Dorigo, Xiaoxue Han, Liupan An, Federico Leo Redi, Plamen Hristov Hopchev, Thibaud Humair, Maxime Schubiger, Hang Yin, Guido Andreassi, Violaine Bellée, Olivier Göran Girard, Axel Kuonen, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Albert Puig Navarro, Evgenii Shmanin, Lino Ferreira Lopes, Dipanwita Dutta, Zheng Wang, Yi Wang, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Giovanni Carboni, Victor Coco, Adam Davis, Paolo Durante, Yu Zheng, Anton Petrov, Maxim Borisyak, Feng Jiang, Zhipeng Tang, Luis Alberto Granado Cardoso, Xuan Li