Pattern Recognition and Event Reconstruction in Particle Physics Experiments

This report reviews methods of pattern recognition and event reconstruction used in modern high energy physics experiments. After a brief introduction into general concepts of particle detectors and statistical evaluation, different approaches in global and local methods of track pattern recognition are reviewed with their typical strengths and shortcomings. The emphasis is then moved to methods which estimate the particle properties from the signals which pattern recognition has associated. Finally, the global reconstruction of the event is briefly addressed.Comment: 101 pages, 58 figure

Observation of charmless B meson decays

Using the ARGUS detector at the e$^+$e$^−$ storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π± and pp̄π+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 Vub is non-zero

Measurement of the Decays τ−→K∗\tau^- \to K^* ντ\nu_\tau and τ−→ρ−ντ\tau^- \to \rho^- \nu_\tau

Using the ARGUS detector at DORIS II, we have determined the branching ratios for the decays τ−→K*−vτ and τ−→ρ−vτ to be (1.23 ±0.21−0.21+0.11)% and (21.5±0.4±1.9)%, respectively. These results are in agreement with theoretical expectations based on the standard model

Inclusive ϕ\phi-meson production in electron-positron interactions in the energy region of the Υ\Upsilon-resonances

We report on a high precision measurement of ϕ-meson production in continuum events and in direct decays of the Υ(1S)- and Υ(2S)-mesons. The ratio of the total production rate of ϕ-mesons in direct Υ(1S)- and Υ(2S)-decays over that in continuum events is 1.32±0.08±0.09 and 1.07±0.13±0.11 respectively. This is compatible with the corresponding ratio obtained for lighter mesons, but is appreciably smaller than the relative baryon production rate

Lifetimes of charmed mesons

Using the ARGUS detector at the e+e− storage ring DORIS II at DESY, we have measured the lifetimes of the D$^0$, D$^+$ and D$^{+S}$ mesons. We find τD$^0$ = (4.8$^{±0.4}$$_{±0.3}$) × 10$^{−13}$ s, τD+ = (10.5$^{±0.8}$$_{±0.7}$) × 10$^{−13}$ s and τD +S = (5.6$^{+1.3}$$_{−1.2±0.8}$) × 10$^{−13}$ s

Search for b→\tos gluon in B meson decays

Using the ARGUS detector at the $e^+e^−$ storage ring DORIS II at DESY, a search for penguin decays of B mesons involving b→s gluon has been performed. No evidence for the penguin mechanism was found and a number of upper limits are quoted

Search for hadronic b→\tou 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

Search for b→\tos gluon in B meson decays

Using the ARGUS detector at the $e^+e^−$ storage ring DORIS II at DESY, a search for penguin decays of B mesons involving b→s gluon has been performed. No evidence for the penguin mechanism was found and a number of upper limits are quoted