J.P. Donker

Observation of B0-B0 mixing

Abstract Using the ARGUS detector at the DORIS II storage ring we have searched in three different ways for B0- B 0 mixing in ϒ (4S) decays. One explicitly mixed event, a decay ϒ (4S)→B0B0, has been completely reconstructed. Furthermore, we observe a 4.0 standard deviation signal of 24.8 events with like-sign lepton pairs and a 3.0 standard deviation signal of 4.1 events containing one reconstructed B0( B 0) and an additional fast l+(l)−. This leads to the conclusion that B0- B 0 mixing is substantial. For the mixing parameter we obtain r=0.21±0.08.

An improved upper limit on the ντ-mass from the decay π−→π−π−π−π+π+ντ

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have observed the decay τ − → π − π − π − π + π + ν τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m ( ν τ ) c 2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

B meson decays into charmonium states

Abstract Using the ARGUS detector at the e +e− storage ring DORIS II, we have studied the colour-suppressed decays B → J ψ X and B→ψ′ X. We find the inclusive branching ratios for these two channels to be (1.07±0.16±0.19) % and (0.46±0.17±0.11) %, respectively. From a sample of reconstructed exclusive events the masses of the B0 and B+ mesons are determined to be (5279.5±1.6±3.0) MeV c 2 and (5278.5±1.8±3.0) MeV c 2 , respectively. Branching ratios are determined from five events of the type B 0 → J ψ K ∗0 and three of B+→J/ψ K+. In the same data sample a search for B0→e+e−, μ+μ− and μ±e∓ leads to upper limits for such decays.

An Improved Upper Limit on the tau-neutrino Mass from the Decay tau- ---> pi- pi- pi- pi+ pi+ tau-neutrino

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have observed the decay τ − → π − π − π − π + π + ν τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m ( ν τ ) c 2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

Evidence for the decay τ−→ντωπ−

Abstract Using the ARGUS detector at DORIS II, we have analyzed tau decays into π − π − π + π 0 ν τ . The branching ratio was determined to be (4.2±0.5±0.9)%. From a study of the three pion sub-system, we find evidence for the decay τ − → ωπ − ν τ with a branching ratio of (1.5±0.3±0.3)%. The ωπ − system is found to be predominantly in a J P =1 − state. There is no evidence for second-class axial-vector currents. The spectral function for the ωπ − final state is in agreement with a prediction based on CVC and σ e + e −→ ωπ 0 .

Measurement of tau decays into three charged pions

We report a study of the decay τ−→τ−τ+τ−vτ using the ARGUS detector at the DORIS II storage ring. Tau pairs were produced bye+e− annihilation at centre-of-mass energies near 10 GeV. We have observed about 1,700 events, corresponding to a branching ratio for τ−→τ−τ+τ−vτ of (5.6±0.7)%. The dominant mode for this decay is observed to beρ0π− in aJp=1+ spin state. Theρ0π− mass spectrum shows a broad enhancement near 1.10 GeV/c2, which has the properties expected for theA1.

Reconstruction of B mesons

Abstract B mesons have been reconstructed in five decay channels of the type B →D ∗ ±nπ(n=1,2,3) using data accumulated by the ARGUS experiment at the e + e − storage ring DORIS II at DESY. In total, we find 40 neutral B mesons above a background of 15±6 events with a mass of (5278.2±1.0±3.0) MeV/ c 2 and 32 charged B mesons above a background of 17±6 events with a mass of (5275.8±1.3±3.0) MeV/ c 2 . The decays B 0 D ∗+ π − π 0 , B 0 D ∗+ π − π − π + , and B − → D ∗+ π − π − π 0 have been observed for the first time. We find substantially smaller branching ratios for the decay modes B 0 → D ∗+ π − and B − → D ∗+ π − π − than previously published by the CLEO collaboration.

First observation of γγ→K∗0K∗0

Abstract The final state K + K − π + π − has been studied in γγ interactions using the ARGUS detector at the e + e − storage ring DORIS II at DESY. Production of the vector meson pair K ∗0 (892) K ∗0 (892) is observed for the first time. The cross section for K + K − π + π − , K ∗0 K − π + +c.c. and K ∗0 K ∗0 are all found to be of the order of a few nb. In the W γγ range accessible, a mean upper limit of 0.5 nb at 95% CL is derived for φϱ 0 production.

Observation of octet and decuplet hyperons in e+e− annihilation at 10 GeV centre-of-mass energy

Abstract Results on hyperon production are reported for data accumulated at 10 GeV centre-of-mass energy with the ARGUS detector. Signals for both the octet states Λ, Σ 0 and Ξ − and the decuplet states Σ ± (1385), Ξ 0 (1530) and Ω − are observed 1 (references to a specific state are to be interpreted as also implying the charge conjugate state), some for the first time in e + e − annihilation. Baryon rates from γ dir (1S) decays are enhanced by a factor of about 3 over the continuum.

Determination of αs from a measurement of the direct photon spectrum in Γ(1S) decays

Abstract Using the ARGUS detector at the DORIS II e + e − storage ring we have measured direct photons from the decay ???(1 S )→ γgg . The ratio R γ = Γ (???(1S)→ γgg )/ Γ (???(1S)→ ggg )=(3.00±0.13±0.18)% has been determined, from which we deduce values of the strong coupling constant α s =0.225±0.011±0.019 and the QCD scale parameter Λ MS =115±17±28 MeV defined in the modified minimal-subtraction scheme. The shape of the measured spectrum clearly rules out the predictions of the lowest order QCD calculations.