A Search for the Electric Dipole Moment of the Tau-Lepton

Using the ARGUS detector at the e+e- storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor d_tau of the tau lepton in the production of tau pairs at q^2=100 GeV^2. This is the first direct measurement of this CP violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed tau decay products. No evidence for CP violation was found, and we derive the following results: Re(d_tau)=(1.6+-.9)*10^(-16) ecm and Im(d_tau)=(-0.2+-0.8)*10^(-16) ecm, where statistical and systematic errors have been combined.Comment: 8 pages, 5 figures (10 subfigures

A determination of two Michel parameters in purely leptonic tau decays

Using the ARGUS detector at the e+e− storage ring DORIS II, we have determined the Michel parameters ϱ and ξ of τ → μννandτ → eνν decays. From a data sample with 333 events/pb around s= 10GeV, we select 3230 events ǂe+e−→ τ+τ−→ (μ±μμ)(eǂvv) and determine ϱ from the e and μ momentum spectra and ξ from the correlations between e and μ momenta. For ϱ we obtain ϱτ→e = 0.79 ± 0.08 ± 0.06 and ϱτ→μ = 0.76 ± 0.08 in accordance with the V - A structure of the decays. The momentum correlations are only sensitive to the product ξτ→eξτ→μ. Setting ξτ→e = ξτ→μ, we obtain |ξτ| = 0.90 ± 0.15 ± 0.10 also in accordance with V - A. The updated decay fractions are B(τ →evv) = (17.5 ± 0.3 ± 0.5)% and B(τ → μvv) = (17.4 ± 0.3 ± 0.5)%

Measurement of the decay τ⁻→ρ⁻ν_τ

An analysis of the decay $τ-→π^-π^0v_τ$ has been performed using the ARGUS detector at the DORIS II storage ring. The branching ratio has been determined to be Br($τ-→π^-π^0v_τ$=(22.6±0.4±0.9)%. The shape of the π-π0 invariant mass spectrum is found to be in good agreement with the predictions obtained using the conserved vector current (CVC) hypothesis, suggesting that the π-π0 system is produced in a JP=1− state. An analysis of the measured decay angular distribution of the pions with respect to the flight direction of the π-π0 system demonstrates the vector nature of the coupling at the τvτ vertex. With the assumption of zerovτ mass thevτ spin has been shown to be $J_{v_τ}=12$

Measurement of inclusive baryon production in B meson decays

Using the ARGUS detector at the e<sup>+</sup>e<sup>–</sup> storage ring DORIS II at DESY, we have studied B meson decays into baryons p and <span style="text-decoration:overline">p</span> and <span style="text-decoration:overline">p</span> correlations, and various lepton-baryon and lepton-baryon-antibaryon correlations the inclusive branching ratio is found to be BR (B→baryons)=(6.8±0.5±0.3)%

Observation of a new charmed baryon

Using the ARGUS detector at the e<sup>+</sup>e<sup>−</sup> storage ring DORIS II at DESY, we have observed a new charmed baryon state in the channel Λc<sup>+</sup>π<sup>+</sup>π<sup>−</sup>. (All references to a specific charged state also imply the charge conjugate state.) The mass of this state was measured to be (2626.6 ± 0.5 ± 1.5) MeV/c<sup>2</sup>. The product of the production cross section and branching ratio for this channel was determined to be (11.5 ± 2.5 ± 3.0) pb, and the natural width estimated to be smaller than 3.2 MeV/c<sup>2</sup> at 90% CL

New results on D0\mathrm{D^0} decays

Using the ARGUS detector at the $e^+e^−$ storage ring DORIS II, we have studied nine decay modes of theD0 meson. In addition to a higher-precision determination of the branching ratios for these modes, several new channels, the decays $D^0 \to \bar K^0 \eta ',D^0 \to \bar K^{*0} \omega$ and $D^0 \to \bar K\pi ^ + \omega$ , have been observed for the first time

Analysis of the decay τ−→π−π−π+vτ\tau^- \to \pi^-\pi^- \pi^+v_\tau and determination of thea 1(1260) resonance parameters

Using the ARGUS detector at the DORIS II $e^+e^−$ storage ring we have studied the three-pion hadronic final state in the decay $τ^- → π^-π^-π^+v_τ$. From about 7500 events we conclude that the three-pion system is dominated by the $J^P=1^+$ resonancea1 (1260) decaying preferentially via $ρ^0π^-$. Our data restrict a possible ρπ contribution of three-pion states without intermediate resonances to less than 6% at 95% CL. Fitting a model by Isgur et al. to the data yieldsma1=(1.211±0.007±0.0500.0)GeV/c$^2$ and $Γ$a1=(0.446±0.0021±0.1400.0)GeV/c$^2$. The second errors reflect the model dependence of the result. This is the currently most significant determination of thea1 resonance parameters. The ratio ofS- and D-wave amplitudes for the ρ0π- intermediate state of thea1− decay at the nominala1− mass was found to beD/S=−0.11±0.02. Using thisD/S ratio we update our former measurement of the parity violating asymmetry parameterγ $AV=2gAgV/(g^2_A+g^2_V)$ to 1.25±0.23±0.080.15. The branching ratio of the decay $τ^- → π^-π^-π^+v_τ$ is determined to be Br($τ^- → π^-π^-π^+v_τ$)=(6.8±0.1±0.5)%

Observation of semileptonic charmless B meson decays

A detailed study of the lepton momentum spectrum in υ(4S) decays has been made using the ARGUS detector at the DORIS II e+e− storage ring at DESY. In the region from 2.3 to 2.6 GeV/c, which is above the endpoint for contributions from B decays via b→c transitions, we observe 41±10 events in excess of known backgrounds. These events are interpreted as a signal for b→u transitions. A model dependent value of 0.10±0.01 is obtained for the ratio of Cabibbo-Kobayashi-Maskawa matrix elements |Vub|/|Vcv|, using the Altarelli et al. model