Observation of the decay D_s1 (2536)→D*⁰K⁺

Using the ARGUS detector at the e+e- storage ring using DORIS II at DESY, we have observed a new decay channel for the excited charm-strange meson $D_{s1}(2536)^+→D^{∗O}K^+$. The production cross section for the $D_{s1}(2536)^+$ decaying via this channel is measured to be $σ (D_{s1}(2536)^+$)·BR($D_{sl}(2536)^+→D^{∗0}K^+$)= 18±4±3 pb at ECM = 10.4 GeV. The mass of the $D_{s1}(2536)^+$ is found to be 2535.2 ± 0.5±1.5 MeV/c$^2$ in agreement with the value obtained from an analysis of the $D_{s1}(2536)^+→D^{∗+}K^0_s$ decay channel. The natural width is determined to be less than 3.9 MeV/c2 at 90%CL

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)%

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)%

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

Measurement of the decay B^-→D^*0ℓ^-<span style="text-decoration:overline">&#955;</span>

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY we have studied the decay , where ℓ− = e− or μ−, using the D0γ and D0π0 decay modes of the D∗0 meson. B mesons were produced in 209 000 decays of γ(4S). Assuming electron-muon universality, we obtain a value for the branching ratio of BR($B^- \rightarrow D^{*0} l^- λ = 5.8 \pm 1.4 \pm 1.3$)%

Observation of a new charmed baryon

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have observed a new charmed baryon state in the channel Λc+π+π−. (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/c2. 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/c2 at 90% CL

A measurement of the tau mass

Using the ARGUS detector at the DORIS II storage ring, a new measurement of the mass of the τ lepton has been obtained. An analysis of the tau pseudomass spectrum for decays of the type τ− → π−π−π+ντ finds mτ = 1776.3±2.4±1.4 MeV/c&lt;sup&gt;2&lt;/sup&gt;. This result also leads to an improvement of the upper limit on the ντ mass to mντ &#60; 31 MeV/c2 at the 95% confidence level