K. Reim

Measurement of the decay

Using the ARGUS detector at the e + e − storage ring DORIS II at DESY we have investigated the decays B 0 → D ∗− e + v and B 0 →D ∗− μ + ν. The B 0 mesons were produced in 39600 ϒ(4 S )→ B 0 B 0 decays. Assuming electron-muon universality we obtain a branching ratio BR ( B 0 → D ∗− e + v)= BR ( B 0 → D ∗− γm + ν)=(7.0±1.2±1.9)% .

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/c2. This result also leads to an improvement of the upper limit on the ντ mass to mντ < 31 MeV/c2 at the 95% confidence level.

Exclusive hadronic decays ofB mesons

Using the ARGUS detector at thee+e− storage ring DORIS II, we have measuredB decays into exclusive final states containing aD orD* meson plus several pions, or containing aJ/ψ or ψ′ meson plus a strange particle. Some of these channels have not been seen before, while others represent updated measurements of previous results. The branching ratios are compared with the predictions of the model of Bauer, Stech and Wirbel. Using the cleanest decay channels, the mass of the charged and neutralB meson are found to bemB−=(5280.5±1.0±2.0) MeV/c2 andmB0=(5279.6±0.7±2.0) MeV/c2 respectively, yielding a mass differencemB0−mB−=(−0.9±1.2±0.5) MeV/c2.

Observation of spin-parity 2+ dominance in the reactionγγ→ρ0ρ0 near threshold

The reactionγγ→π+π−π+π− has been studied with the ARGUS detector. The rate in the invariant mass region below 1.8 GeV/c2 is found to be largely due toρ0ρ0 production. A spin-parity analysis shows a dominance of the partial wave (JP,Jz)=(2+, 2) with a small admixture fromJP=0+. The contribution of negative parity states is consistent with zero. The large ratio of cross sectionsσ(γγ→ρ0ρ0)/σ(γγ→ρ+ρ−)≃4, and the dominance of theJP=2+ wave in the reactionγγ→ρ0ρ0 is a signature consistent with the production of an exotic (I=2) resonance.

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.

A Model independent determination of the inclusive semileptonic decay fraction of B mesons

Abstract With the ARGUS detector at the e + e - storage ring DORIS II, we have determined decay fraction and electron momentum spectrum of the inclusive decay mode B → eν X. Usinng lepton tags from the second B meson. in 209 000 γ(4 S ) → B B decays, we could determine the spectrum for all electron momenta p e > 0.6 GeV/ c . Including the small extrapolation to p e > 0, we find the model-independent decay fraction B (B → eν X) = (9.6 ± 0.5 ± 0.4)%. Adding D meson tags, our result is (9.7 ± 0.5 ± 0.4)%.

Measurement of the decay B0→D∗−l+ν

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have investigated the decay B 0 →D − l + ν, where l + is e + or μ + . The B 0 mesons were produced in 150 000 ϒ(4S) decays. Assuming electron-muon universality we obtain a branching ratio BR(B 0 →D − e + ν )=BR(B 0 →D − μ + ν )=(1.8±0.6±0.5)%.

A study of B0 → D∗+ ℓ−vandB0B0 mixing using partial D∗+ reconstruction

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II at DESY, we have studied the decay B 0 → D ∗+ l − v by exploiting a partial D ∗+ reconstruction technique. The branching ratio for this mode was thereby determined to be (4.5 ± 0.3 ± 0.4)%. Using the corresponding sample of tagged B 0 mesons, we measured the B 0 B 0 mixing parameter to be r d = 0.194 ± 0.062 ± 0.054, a result only weakly dependent upon the ratio of semileptonic widths for and production rates of B 0 and B + mesons. We have also determined the branching ratio Br ( B 0 → X l − v to be (9.3 ± 1.1 ± 1.5)%. By comparing the results for full and partial D ∗+ reconstuction we found the absolute branching ratios for D 0 → K − π + and D 0 → K − π + π + π − to be (4.5 ± 0.6 ± 0.4)% and (7.9 ± 1.5 ± 0.9)%, respectively.

Inclusive production ofD0,D+ andD*(2010)+ mesons inB decays and nonresonante+e− annihilation at 10.6 GeV

Using the ARGUS detector at thee+e− storage ring DORIS II at DESY, we have measured the inclusive production ofD0,D+ andD*(2010)+ mesons inB decays and in nonresonante+e− annihilation around 10.6 GeV. The inclusive branching ratios forB decays toD0,D+ andD*+ mesons are found to be (52.2±8.2±3.5)%, (27.2±6.3±3.5)% and (34.8±6.0±3.5)% respectively. Thus,D0 andD+ production account for about 70% of the charm produced inB decays, neglectingb→u contributions to the total width. The production cross sections and momentum spectra for continuume+e− annihilation are also presented.

Observation of a new charmed baryon

Abstract 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 Λ c + 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/ c 2 . 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 2 at 90% CL.