We report the results of a search for the rare, purely leptonic decay B- -> mu(-)(nu) over bar (mu) performed with a 711 fb(-1) data sample that contains 772 x 10(6) B (B) over bar pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B- -> mu(-)(nu) over bar (mu)) = (6.46 +/- 2.22 +/- 1.60) x 10(-7) or a frequentist 90% confidence level interval on the B- -> mu(-)(nu) over bar (mu) branching fraction of [2.9, 10.7] x 10(-7).
Rakesh Chawla, Andrea Rizzi, Matthias Finger, Federica Legger, Matteo Galli, Sun Hee Kim, Jian Zhao, João Miguel das Neves Duarte, Tagir Aushev, Hua Zhang, Alexis Kalogeropoulos, Yixing Chen, Tian Cheng, Ioannis Papadopoulos, Gabriele Grosso, Valérie Scheurer, Meng Xiao, Qian Wang, Michele Bianco, Varun Sharma, Joao Varela, Sourav Sen, Ashish Sharma, Seungkyu Ha, David Vannerom, Csaba Hajdu, Sanjeev Kumar, Sebastiana Gianì, Kun Shi, Abhisek Datta, Siyuan Wang, Anton Petrov, Jian Wang, Yi Zhang, Muhammad Ansar Iqbal, Yong Yang, Xin Sun, Muhammad Ahmad, Donghyun Kim, Matthias Wolf, Anna Mascellani, Paolo Ronchese, , , , , , , , , , , , , , , , , , , , , , , ,
Volkan Cevher, Kimon Antonakopoulos