A. Babaev

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.

Argus: A universal detector at DORIS II

Abstract The detector ARGUS has been designed as a universal tool to investigate final states from e + e − annihilation processes in the energy range of the ϒ resonances. ARGUS started operation in October 1982 and has since successfully taken data at the ϒ(1S), ϒ(2S) and ϒ(4S) energies, and in the nearby continuum. The detector combines excellent charged particle identification and good photon energy resolution over more than 90% of the full solid angle. A particle originating from the interaction vertex and leaving the beam tube traverses the following components: the vertex drift chamber, the main drift chamber which determines its momentum and specific ionization, the time-of-flight system through which its velocity is determined, and the electromagnetic calorimeter. Muons pass through the magnet coils and the flux return yoke and finally hit the muon chamber system which surrounds the detector. The momentum resolution of ARGUS is σ (p T ) P T = (0.01 2 + (0.009p T [ GeV /c]) 2 ) 1 2 , the photon energy resolution in the barrel shower counters is σ (E) E = ( 0.072 2 +0.065 2 E[ GeV ] ) 1 2 . Combining the information from all p devices, more than 80% of all charged hadrons can be recognized unambiguously. The electron-hadron and muon-hadron rejection rates are 1:200 and 1:50 respectively.

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.

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.

Measurement of F-2(c(c)over-bar) and F-2(b(b)over-bar) at high Q(2) using the H1 vertex detector at HERA

Abstract.Measurements are presented of inclusive charm and beauty cross sections in e + p collisions at HERA for values of photon virtuality Q2 > 150 GeV2 and of inelasticity 0.1 < y < 0.7. The charm and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q2 and Bjorken x, and values for the structure functions

Observation of charmless B meson decays

F_2^{c\bar{c}}

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

and

B meson decays into charmonium states

F_2^{b\bar{b}}

Study of inclusive semileptonic B meson decays

are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.