Georg Viehhauser

Abstract:

Based on a sample corresponding to 4.3×10⁶ produced τ-pair events, we have studied hadronic dynamics in the decay τ^-→ντπ^-π ⁰π⁰ in data recorded by the CLEO II detector operating at the CESR e⁺e^- collider. The decay is dominated by the process τ^-→ντa1^-(1260), with the a1^- meson decaying to three pions predominantly via the lowest dimensional (mainly S-wave) ρ^-π⁰ Born amplitude. From model-dependent fits to the Dalitz plot and angular observables in bins of 3 π mass, we find significant additional contributions from amplitudes for a1 decay to σπ, f0(1370)π, and f2(1270)π, as well as higher dimensional a1→ρπ and ρ′ π amplitudes. Notably, the squared σπ amplitude accounts for approximately 15% of the total τ^- →ντπ^-π⁰π⁰ rate in the models considered. The data are well described using couplings to these amplitudes that are independent of the 3π mass. These amplitudes also provide a good description for the τ^- →ντπ^-π⁰π⁰ Dalitz plot distributions. We have searched for additional contributions from τ^-→ντπ′ -(1300). We place 90% confidence level upper limits on the branching fraction for this channel of between 1.0×10^-4 and 1.9×10^-4, depending on the π′ decay mode considered. The π^-π⁰π⁰ mass spectrum is parametrized by a Breit-Wigner form with a mass-dependent width which is specified according to the results of the Dalitz plot fits plus an unknown coupling to an a1→K*K amplitude. From a χ² fit using this parametrization, we extract the pole mass and width of the a1, as well as the magnitude of the K*K coupling. We have also investigated the impact of a possible contribution from the a1′(1700) meson on this spectrum. Finally, exploiting the parity-violating angular asymmetry in a1→3π decay, we determine the signed value of the τ neutrino helicity to be hντ=-1.02±0.13 (stat)±0.03 (syst+model), confirming the left-handedness of the τ neutrino. ©1999 The American Physical Society.

Abstract:

From a data sample of 29058 τ⁺→π^±π⁺π ^-π⁰ντdecays observed in the CLEO detector we derive a 95% confidence upper limit on the tau neutrino mass of 28 MeV. ©2000 The American Physical Society.

Abstract:

We have studied charmless hadronic decays of B mesons into two-body final states with kaons and pions and observe three new processes with the following branching fractions: B(B → π+π−) = (4.3+1.6−1.4±0.5)×10−6, B(B→K0π0)=(14.6+5.9+2.4−5.1−3.3) × 10−6, and B(B → K±π0) = (11.6+3.0+1.4−2.7−1.3) × 10−6. We also update our previous measurements for the decays B → K±π∓ and B± → K0π±. © 2000 American Physical Society.

Abstract:

We have searched for rare and forbidden decays of the η′ meson in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb⁻¹ of e⁺e⁻ collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring. We find no signals and set 90% confidence level upper limits of their branching fractions: B(η′→e⁺e⁻η)<2.4×10⁻³, B(η′→e⁺e⁻π⁰)<1.4×10⁻³, B(η′→e⁺e⁻γ)<0.9×10⁻³, and B(η′→eμ)<4.7×10⁻⁴. We also fit the matrix element of the η′→π⁺π⁻η Dalitz plot with the parametrization |M|²=A|1+αy|², where y is a linear function of the kinetic energy of the ηand find Re (α)=−0.021±0.025. © 2000 The American Physical Society.