J. Spengler

Search for hadronic b→u decays

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we searched for b→u transitions in exclusive hadronic B meson decays. A systematic analysis of B decays into pions has been performed for decay modes with 2–7 pions in the final state. In none of the decays a positive signal was observed. The upper limits obtained on various branching ratios are consistent with the current model predictions.

Observation of Semileptonic Charmless B Meson Decays

Abstract A detailed study of the lepton momentum spectrum in υ (4 S ) decays has been made using the ARGUS detector at the DORIS II e + e − storage ring at DESY. In the region from 2.3 to 2.6 GeV/ c , which is above the endpoint for contributions from B decays via b → c transitions, we observe 41±10 events in excess of known backgrounds. These events are interpreted as a signal for b → u transitions. A model dependent value of 0.10±0.01 is obtained for the ratio of Cabibbo-Kobayashi-Maskawa matrix elements | V ub |/| V cv| , using the Altarelli et al. model.

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)% .

Production and transport of conduction electrons in a liquid argon ionization chamber

Abstract Free electrons produced by α- and β-particles in a liquid argon ionization chamber have been detected. For minimum ionizing particles the collected charge saturates at a field strength of E ⪅ 15 kV/cm. 95±4)% of the produced electrons were collected. For strongly ionizing α-particles no saturation was observed up to a field strength of 40 kV/cm, where (25±3)% of the produced electrons were detected. The influence of oxygen and nitrogen, solved in the liquid argon, on the charge collection was studied. A nonlinear relationship between the mean free path length for absorption and the applied electric field indicates the existence of hot electrons in liquid argon. The recombination effect in the ionization column produced by α-particles is enhanced by oxygen and nitrogen impurities in liquid argon.

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 charmless B meson decays

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have observed charmless decays of B mesons into the final states ppπ ± and ppπ + π − . The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10 −4 for the three-body and (6.0±2.0±2.2)×10 −4 for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element V ub is non-zero.

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)%.

Density, charge and transverse momentum correlations of particles in non-diffractive proton-proton collissions at √s = 52.5 GeV

Abstract Inelastic events with an observed charged multiplicity n obs ⩾ 7 have been studied at the CERN ISR using the split field magnet detector. Correlations of particle densities, charges and transverse momenta have been determined and a phenomenological analysis in the framework of cluster models has been performed. A good description of all results is obtained if one allows for charged clusters, produced in a mechanism with limited charge exchange. The mean transverse momentum of clusters is 0.65 ± 0.10 GeV/ c . Short-range correlations of particles of like charge due to the Bose-Einstein effect can be described as a second-order interferrence phenomenon with a radius R = 1.34 ± 0.31 fm and a lifetime of cτ = 1.38 ± 0.60 fm for the pion source.

Study of inclusive semileptonic B meson decays

Abstract Using the ARGUS detector at the e + e − storage ring DORIS-II, we have measured the inclusive semileptonic decays of B-mesons into electrons and muons. The data originate from 220.5 events/pb on the ϒ(4S) resonance. We find BR (B→e + v e X = (10.3 ± 0.6 ± 0.2)% and BR (B→ μ + v μ X) = (10.0 ± 0.6 ± 0.2)% using the model of Altarelli et al. for extrapolating over all lepton momenta, and BR (B→e + v e X) = (9.9±0.6)%, BR(B→ μ + v μ X) = (9.7±0.6)% using the model of Grinstein et al. For semileptonic decays into baryons, we obtain an upper limit of BR ( B → p e + v X ) CL ) .