P. Križan

Measurement of the polarization in the decay B → J/ψK∗

Abstract Polarization in the exclusive decay B → J/ψK ∗ was measured using the ARGUS detector at the e+e− storage ring DORIS II. The ratio of the transverse to the total decay width was found to be ΓT/Γ = 0.03±0.16±0.15. This measurement demonstrates that the B 0 → J/ψK ∗0 decay channel can be effectively used for CP violation studies.

Determination of the Michel parameters ξ and δ in leptonic τ decays

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have determined the Michel parameters ξ and δ of τ ∓ → l ∓ ν ν - decays. With an integrated luminosity of 445 pb −1 around s = 10 GeV, we have produced approximately 415000 τ-pairs. From this data sample, 3262 events were selected with e + e − → τ + τ − → (l ± ν ν - ) (π ∓ π + π − ν) . The semihadronic decay was used as analyser of the τ-spin and made possible - owing to the spin correlations - the determination of the parity-violating Michel parameters ξ and δ in the decay τ ∓ → l ∓ ν ν - . Simultaneously to the determination of the Michel parameters, a measurement of the τ-neutrino helicity h ν τ in the decay τ ∓ → π ∓ π + π − ν was obtained. We observed h ν τ = −0.85 −0.17 +0.15 ± 0.05, ϱ = 0.721 ± 0.040 ± 0.021, ξ = 1.26 −0.26 +0.30 ± 0.09, and ξδ = 0.77 −0.16 +0.18 ± 0.05. In addition, the combined ARGUS result on h ν τ , ϱ, ξ, and ξδ are reported using this work and previous measurements.

A search for the electric dipole moment of the τ-lepton

Abstract 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 dτ of the τ lepton in the production of τ 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 τ decay products. No evidence for CP violation was found, and we derive the following results: Re (d τ )=(1.6±1.9)·10 −16 e cm and Im (d τ )=(−0.2±0.8)·10 −16 e cm , where statistical and systematic errors have been combined.

Determination of the structure of τ decays in the reaction e+e− → τ+τ− → ϱ+vτϱ−vτ and a precision measurement of the τ-neutrino helicity

Abstract Using the ARGUS detector at the DORIS II storage ring we have investigated the Lorentz structure of the electroweak interaction in semi-hadronic τ decays. Spin correlations in the process e + e − → τ + τ − → v τ π + π 0 v τ π − π 0 are exploited for a measurement of the normalized product of the vector ( g V ) and axial vector ( g A ) couplings of the τ lepton, γin AV = 2 Re {g A g V ∗ } (|g V | 2 ) . The correlations are sensitive to the product of the couplings in both τ decays: γ AV 2 = γ AV (τ − → ν τ W − ) AV = −h(v τ )h( v τ ) . The measured value, γ AV 2 = 1.044±0.057±0.060, determines the relative sign of the neutrino helicities. Assuming CP invariance, the absolute value | γ AV | = 1.022±0.028±0.030 was found to be incellent agreement with the Standard Model. The contribution of scalar ( g s ) or pseudoscalar ( g P ) couplings was also investigated. No evidence for a scalar-like coupling was found.

Measurement of the absolute branching fractions for D0 decays into K− π+, K− π+ π+ π−, K0 π+ π−

Abstract Using the ARGUS detector at the e+ e− storage ring DORIS II we have measured the absolute branching ratios of the D0 meson, Br(D0→K− π+)=(3.41±0.12±0.28)%, Br(D0→K− π+ π+ π−)=(6.80± 0.27±0.57)%, and Br (D 0 → K 0 π + π − )=(5.03±0.39±0.49)% .

Search for rare B decays

Abstract Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have searched for decays b → sgluon through full reconstruction of a whole event. Two B B decays were found with one of B meson decaying into a final state without charmed particles. We also obtained an upper limit of Br(B+ → τ+ντ) of 1.04% at 90% CL.

Observation of γγ → φϱ0 and γγ → φω

Abstract Two-photon production of the hadronic final states K + K − π + π − and K + K − π + π 0 π − has been studied using the ARGUS detector at the e + e − storage ring DORIS II at DESY. The cross sections of the reactions γγ → oϱ 0 and γγ → oω have been measured for the first time. In addition, angular distrubutions have been determined for the reaction γγ → oϱ 0 → K + K − π + π − .

Determination of the Michel parameters ρ, ξ, and δ in τ-lepton decays with τ→ρν tags

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have measured the Michel parameters ρ , ξ , and ξδ for τ ± →l ± ν ν decays in τ -pair events produced at center of mass energies in the region of the ϒ resonances. Using τ ∓ → ρ ∓ ν as spin analyzing tags, we find ρ e =0.68±0.04±0.08, ξ e =1.12±0.20±0.09, ξδ e =0.57±0.14±0.07, ρ μ =0.69±0.06±0.08, ξ μ =1.25±0.27±0.14 and ξδ μ =0.72±0.18±0.10. In addition, we report the combined ARGUS results on ρ , ξ , and ξδ using this work und previous measurements.Using the ARGUS detector at the

Two measurements of B0B0 mixing using kaon tagging

e^+ e^-

Measurement of the semileptonic branching fractions of the D0 meson

storage ring DORIS II, we have measured the Michel parameters