The and B (0) mixing frequencies, Delta m (s) and Delta m (d) , are measured using a data sample corresponding to an integrated luminosity of 1.0 fb(-1) collected by the LHCb experiment in pp collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8x10(6) candidate events are selected of the type (+ anything), where about half are from peaking and combinatorial backgrounds. To determine the B decay times, a correction is required for the momentum carried by missing particles, which is performed using a simulation-based statistical method. Associated production of muons or mesons allows us to tag the initial-state flavour and so to resolve oscillations due to mixing. We obtain < The hypothesis of no oscillations is rejected by the equivalent of 5.8 standard deviations for and 13.0 standard deviations for B (0). This is the first observation of mixing to be made using only semileptonic decays.
Jian Wang, Lesya Shchutska, Olivier Schneider, Yiming Li, Yi Zhang, Aurelio Bay, Guido Haefeli, Christoph Frei, Frédéric Blanc, Tatsuya Nakada, Michel De Cian, François Fleuret, Elena Graverini, Renato Quagliani, Federico Betti, Aravindhan Venkateswaran, Vitalii Lisovskyi, Sebastian Schulte, Veronica Sølund Kirsebom, Elisabeth Maria Niel, Ettore Zaffaroni, Mingkui Wang, Zhirui Xu, Chao Wang, Lei Zhang, Ho Ling Li, Mark Tobin, Minh Tâm Tran, Niko Neufeld, Matthew Needham, Maurizio Martinelli, Vladislav Balagura, Donal Patrick Hill, Liang Sun, Xiaoxue Han, Liupan An, Federico Leo Redi, Maxime Schubiger, Hang Yin, Violaine Bellée, Preema Rennee Pais, Pavol Stefko, Tara Nanut, Maria Elena Stramaglia, Yao Zhou, Tommaso Colombo, Vladimir Macko, Guillaume Max Pietrzyk, Evgenii Shmanin, Maxim Karpov, Simone Meloni, Xiaoqing Zhou, Surapat Ek-In, Carina Trippl, Sara Celani, Marco Guarise, Serhii Cholak, Dipanwita Dutta, Zheng Wang, Yong Yang, Yi Wang, Hao Liu, Hans Dijkstra, Gerhard Raven, Peter Clarke, Frédéric Teubert, Giovanni Carboni, Victor Coco, Shuai Liu, Adam Davis, Paolo Durante, Yu Zheng, Anton Petrov, Maxim Borisyak, Feng Jiang, Alexey Boldyrev, Almagul Kondybayeva, Hossein Afsharnia