Selected physics results from Belle

Abstract

We present an updated measurement of sin 2 φ 1 in B 0 → c cW decays and first evidence for CP-violating asymmetries in B → π + π − decays. We also report the first observation of the ν c (2 S) meson. The results are based on analyses of a sample of 41.8 million B B meson pairs from the decays of the υ(4 S) resonance, collected with the Belle detector at the KEKB asymmetric-energy e + e − collider. For the B → π + π − CP-violating asymmetry measurement, we fully reconstruct one neutral B meson as a B → π + π − CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the dependence of the asymmetry on the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S ππ = −1.21 −0.27 +0.38( stat) −0.13 +0.16( syst) and A gpπ = +0.94 −0.31 +0.25( stat) ± 0.09( syst). In the η c (2 S) meson search, we examined the K s K − π + invariant mass distribution in a sample of exclusive B → KK S K − π + decays. We find a narrow peak mass M = 3654 ± 6( stat) ± 8( syst) MeV/ c 2 and width Γ < 55 MeV/ c 2. The properties agree with heavy-quark potential model expectations for the η c (2 S) meson, the n = 2 singlet S-wave charmonium state.