Using the ARGUS detector at the e+e storage ring DORIS II at DESY, we have studied lepton energy spectra in ~decays. We present a "pseudo-rest-frame" technique in which the second r in the event, decaying into a heavy hadronic system, is used as reference. This method allows for the first measurement of the Michel Parameter 7/ in ~decays. We also determine the Michel Parameter p in 7" --~ e~u decays with a precision comparable to the present world average. The measured values of the parameters p = 0.735 40.036 40.020 and r 1 = 0.03 40.18 40.12 are in good agreement with standard V-A coupling at the ~--~,-W vertex. 0370-2693/95/$09.50 Q 1995 Elsevier Science B.V. All rights reserved S S D I 0 3 7 0 2 6 9 3 ( 9 4 ) 0 1 3 8 6 1 442 ARGUS Collaboration/Physics Letters B 341 (1995) 441-447 Michel parameters [ 1-3 ] describing the space-time structure of the weak leptonic decays have been determined with high accuracy [4]. All values are in perfect agreement with the Standard Model predictions. The 7lepton discovered in 1975 [5], with its two leptonic decays 7" ~ e~ , and 7" --~/x~u, offers a unique opportunity to study the universality of the charged weak interaction. Describing the leptonic 7" decay by the most general four-fermion Hamiltonian we get the following matrix element [6]:

An analysis of the reaction yy ~ r/c was l~erformed in five different decay channels of the r/c: /~sK+~r ~, K+K-Tr+~ ", 27r+21r , ~b~b and 2K+2K . A value Fry(r/c) = ( 11.3 + 4.2) keV was obtained for the radiative decay width by combining the results from the first four channels. Using our result on the two-photon width we also determined the branching ratio for the decay r/c --~ 2K+2K . 0370-2693/94/$07.00 (~) 1994 Elsevier Science B.V. All rights reserved SSDI 0 3 7 0 2 6 9 3 ( 9 4 ) 0 1 1 1 6-8 ARGUS Collaboration / Physics Letters B 338 (1994) 390-396 391 The measurements of the radiative decay widths of hadrons have proved to be one of the most important tools to study the composition and the properties of the bound states of strong interactions. While for light quarks the understanding of the binding forces is still on a more phenomenological level, in heavy quark systems, such as charmonium, fundamental tests of QCD dynamics can be made. One of the important quantities in the charmonium system is the relation between the leptonic decay width of the J/qt and the two-photon width of the r/c which is to the lowest order given by (see for example [ 1 ] ) Frr (r&) = 3e~( Ms/¢ )2. r,+e_ ( J l Cs ) " --~< QCD corrections have been calculated to order as by Barbieri et al. [2] resulting in the relation Frr(~7~) = Fete ( J / O ) " (1 ~a+O.OT~ which, together . . . . _0.05.1, with Fe+ e(J/~b) = (5.36:t:0.29) keV [31, yields the prediction Frr(r/c) = (8.6 + 0.6) keV. Furthermore, with the assumption that the hadronic r/c decays can be described by the lowest order two-gluon diagram one obtains the ratio of the hadronic to two-photon partial width Fhadrons(~'lc)/Fyr(rlc) proportional to ( a s / a ) 2. This relation could in principle be used to determine as. However, in this case the QCD radiative corrections seem to be too large to provide a reliable prediction. The radiative decay width Frt(r/~) has been measured by two different methods: in photon-photon collision experiments [4-7] and by the measurement of the process p/~ --* ~ [ 8 ]. The most significant results I DESY, IfH Zeuthen 2 Supported by the German Bundesministerium for Forschung und Technologic, under contract number 05413051P. 3 Supported by the German Bundesministerium for Forschung und Technologie, under contract number 056DDI 1P. 4 Supported by the German Bundesministerium ?dr Forschung und Technologie, under contract number 054ERI2R 5 Supported by the German Bundesministerium ?dr Forschung und Technologie, under contract number 055HD21P. 6 University of Toronto, Toronto, Ontario, Canada. 7 McGill University, Montreal, Quebec, Canada. 8 Supported by the Natural Sciences and Eagineering Research Council, Canada. 9 Supported by the German Bundesministerium ?dr Forschung und Technologie, under contract number 055KA l 1R l0 Supported by the Ministry of Science and Technology of the Republic of SIovenia and the Intemationales Bilro KfA, Jiilich. were obtained from the analysis of the decay channel r/¢ --* K~sK+cr :F, where a good identification of the/~s was achieved by determining its decay vertex. The results range from 4 to 27 keV and have large errors because of the small number of collected r& events and uncertainties in the knowledge of r/c branching ratios. The present analysis aims at improving the precision of the Fr~ (r/c) measurement by using several decay channels of the r/c meson. The data used in this analysis were collected using the ARGUS detector at the e+e storage ring DORIS II at DESY, and correspond to an integrated luminosity of 473 pb t . The beam energies varied between 4.7 and 5.3 GeV. The ARGUS detector and details about its trigger and its particle identification capabilities were described elsewhere [9]. In what follows, we describe the main features of the analysis, while details can be found in Refs. [10,11]. The two-photon production of the r/c was studied in e+e interactions via the reaction

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.

Using the ARGUS detector at the e(+)e(-) storage ring DORIS II, we have measured the Michel parameters rho,xi, and xi delta for tau(+/-) --> l (+/-) v (v) under bar decays in tau-pair events produced at center of mass energies in the region of the tau resonances. Using tau(-/+) --> rho(-/+) v as spin analyzing tags, we find rho(e) = 0.68 +/- 0.04 +/- 0.08, xi(e) = 1.12 +/- 0.20 +/- 0.09, xi delta(e) = 0.57 +/- 0.14 +/- 0.07, rho(mu)= 0.69 +/- 0.06 +/- 0.08, xi(mu) = 1.25 +/- 0.27 +/- 0.14 and xi delta(mu) = 0.72 +/- 0.18 +/- 0.10. In addition, we report the combined ARGUS results on rho, xi, and xi delta using this work and previous measurements. (C) 1998 Elsevier Science B.V. All rights reserved.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have found evidence for the production of the excited charmed baryon state Λc(2593)+ in the channel Λc+π+π−. Its mass was determined to be (2594.6±0.9±0.4) MeV/c2, and the natural width measured to be Γ = (2.9−2.1−1.4+2.9+1.8) MeV. The production cross section times the branching ratios of σ(e+e− → Λc(2593)+X) × Br(Λc(2593)+ → Λc+π+π−) × Br(Λc+ → pK−π+) was measured to be (0.25−0.13+0.24 ±0.13) pb. The fractions of Λc(2593)+ decays proceeding through the Σc0π+ and Σc++π− channels were determined to be 0.29±0.10±0.11 and 0.37±0.12±0.13, respectively.

A maximum likelihood analysis of ARGUS data on two-photon production of π+π+π0π0π−π− is presented. A small fraction of events is due to the production of omega pairs. The γγ → ωω cross section has its maximum value close to threshold.

The two-photon reaction $\gamma\gamma\to\pi^+\pi^-\pi^0$ was investigated by the ARGUS collaboration. The reaction is dominated by the formation of the $a_2(1320)$ meson. A value of $\Gamma _{\gamma \gamma} = (0.96 \pm 0.03 \pm 0.13)$ keV was obtained for its radiative width, in good agreement with the world average. The fraction of $\gamma\gamma$-helicity 0 in the $a_2$ two-photon width was found to be equal to $(6.7\pm 2.2)\%$. It allows a discrimination among models that describe the dynamics in the two-photon production of tensor mesons. An upper limit of $\Gamma _{\gamma \gamma} \cdot {\rm Br}(\rho ^{\pm} \pi ^{\mp}) keV (90% c.l.) was obtained for the resonance $\pi (1300)$. The partial wave analysis revealed almost a complete absence of the wave with spin and parity $J^P=2^-$. We also observe no significant enhancement in the $\pi^+\pi^-\pi^0$ invariant mass spectrum that could be attributed to the two-photon production of the $\pi_2(1670)$. The obtained upper limit $\Gamma_{\gamma\gamma}(\pi_2(1670)) keV at the 90% confidence level is in contradiction with two previous observations.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have made two measurements of the mixing parameter χd using kaons as flavour tags. Using D∗+ K± correlations we found χd = 0.20 ± 0.13 ± 0.12 and from the study of (D∗+ℓ−) K± correlations we obtained χd = 0.19 ± 0.07 ± 0.09. The branching ratio for B → D∗+ X has been updated: Br(B → D∗+ X) = (19.6 ± 1.9)%. We have also determined the average multiplicity of charged kaons in B0 decays to be 0.78 ± 0.08.

The impact of the ARGUS experiment to elementary particle physics is reviewed. More than ten years of data taking has allowed ARGUS to contribute significantly to our understanding of beauty and charmed hadrons, τ Leptons, ϒ mesons, ϒϒ interactions and fragmentation processes. In particular the ARGUS measurements of CKM matrix elements opened up a new window on the Standard Model.

Using the ARGUS detector at the e+e− storage ring DORIS II, we have measured the semileptonic branching ratios of the D0 meson to be Br(D0 → e+νeX) = (6.9 ± 0.3 ± 0.5) % and Br(D0 → μ+νμX) = (6.0 ± 0.7 ± 1.2) %, and the semileptonic branching ratio of the charmed hadron mixture from e+e− annihilation around 10 GeV to be Br(c → e+νeX) = (9.6 ± 0.4 ± 1.1) %.

Using the ARGUS detector at the storage ring DORIS II we have measured tau decays into three charged mesons containing K* mesons. Exploiting the good particle identification capabilities of the detector we have determined the following branching ratios: Br(tau(-) --> <(K*(0))over bar>pi(-)nu(tau)) = (0.25 +/- 0.10 +/- 0.05) %, Br(tau(-) --> K*(0)K(-)nu(tau)) = (0.20 +/- 0.05 +/- 0.04) %, and Br(tau(-) --> K*(-)(X(0))nu(tau)) = (1.19 +/- 0.15(-0.18)(+0.13)) %.

The partial decay width into electrons, Gamma(ee), of the Upsilon(1S) and Upsilon(2S) resonances have been measured the detector ARGUS at the e(+)e(-) storage ring DORIS II of DESY. Applying the formula of Kuraev and Fadin for the radiative corrections we find: Gamma(ee)(Upsilon(1S)) = (1.32 +/- 0.04 +/- 0.03) keV and Gamma(ee)(Upsilon(2S)) = (0.52 +/- 0.03 +/- 0.01) keV. The total decay width of the Upsilon(4S) resonance and its partial width into electrons have been determined as well. Fitting the data with a generalized Breit-Wigner function with an energy dependent decay width Gamma(s) and a mass shift function m(s), we obtain the following resonance parameters: Gamma(M(2)) = (10.0 +/- 2.8 +/- 2.7) MeV, Gamma(ee) = (0.28 +/- 0.05 +/- 0.01) keV and B-ee = (2.77 +/- 0.50 +/- 0.49). 10(-5). We argue that the disagreement of this result with the world average originates from our more adequate parametrization of the observed Upsilon(4S) resonance cross section.

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY we have measured the parameters of a charmed strange meson D* s2 + (2573) decaying into D0K+. The mass of this state was found to be (2574.5±3.3±1.6) MeV/c 2. The measured value of its width is (10.4±8.3±3.0) MeV and the product of the production cross section and branching ratio for this channel was determined to be (10.6±4.2 −1.2 +2.3 ) pb.