Search for New Physics Using B Meson Decay to Tau Lepton and Neutrino

2014 Fiscal Year Final Research Report

• Project/Area Number: 24740157
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: Nagoya University
• Principal Investigator: HORII Yasuyuki 名古屋大学, 理学(系)研究科(研究院), 助教 (80616839)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: B中間子 / Belle実験 / タウ / ニュートリノ / 荷電ヒッグス

Outline of Final Research Achievements

We measure the branching ratio of B->taunu using the full data sample collected at the Belle experiment. Events with B meson pairs are tagged by reconstructing one of the B mesons decaying into hadronic final states, and B->taunu candidates are detected in the recoil. We find evidence for B->taunu with a significance of 3.0 standard deviations. By combining with the result based on a tag of B meson pairs using semileptonic decays, the branching ratio is evaluated to be (0.96+-0.26)x10-4. A stringent constraint is obtained for the ratio of the vacuum expectation values and the charged Higgs mass in Type II of two Higgs doublet models.
To improve the precision on B->taunu, we have developed a new particle identification system. Optical performance of the quartz radiator, which is a main component of the system, has been measured to be sufficiently high. The method of gluing multiple quartz bars for obtaining a full size of about 2.7 meters has been established.

Free Research Field

素粒子実験