W+2jets production at Tevatron -- VECBOS and CompHEP comparison

Results of calculation of all subprocesses in proton-antiproton collisions which contribute to the W+2jets final state are presented at Tevatron energy. The calculation has been carried out by means of the CompHEP software package. A detail comparison with VECBOS generator results for cross sections and various distributions shows an agreement at the level of Monte-Carlo accuracy. Therefore the additional independent check of VECBOS generator has been done. In complement to the VECBOS generator a new generator based on CompHEP allows to study individual subprocesses like $Wb\bar{b}$ or $Wc\bar{c}$. The last point is important, for instance, for study $Wb\bar{b}$ part of the background for single top or Standard Model Higgs signal at Tevatron.Comment: 8 pages including 4 figures as a gzipped postscript fil

Optimized Neural Networks to Search for Higgs Boson Production at the Tevatron

An optimal choice of proper kinematical variables is one of the main steps in using neural networks (NN) in high energy physics. Our method of the variable selection is based on the analysis of a structure of Feynman diagrams (singularities and spin correlations) contributing to the signal and background processes. An application of this method to the Higgs boson search at the Tevatron leads to an improvement in the NN efficiency by a factor of 1.5-2 in comparison to previous NN studies.Comment: 4 pages, 4 figures, partially presented in proceedings of ACAT'02 conferenc

Reconstruction of potential energy profiles from multiple rupture time distributions

We explore the mathematical and numerical aspects of reconstructing a potential energy profile of a molecular bond from its rupture time distribution. While reliable reconstruction of gross attributes, such as the height and the width of an energy barrier, can be easily extracted from a single first passage time (FPT) distribution, the reconstruction of finer structure is ill-conditioned. More careful analysis shows the existence of optimal bond potential amplitudes (represented by an effective Peclet number) and initial bond configurations that yield the most efficient numerical reconstruction of simple potentials. Furthermore, we show that reconstruction of more complex potentials containing multiple minima can be achieved by simultaneously using two or more measured FPT distributions, obtained under different physical conditions. For example, by changing the effective potential energy surface by known amounts, additional measured FPT distributions improve the reconstruction. We demonstrate the possibility of reconstructing potentials with multiple minima, motivate heuristic rules-of-thumb for optimizing the reconstruction, and discuss further applications and extensions.Comment: 20 pages, 9 figure

LCG MCDB -- a Knowledgebase of Monte Carlo Simulated Events

In this paper we report on LCG Monte Carlo Data Base (MCDB) and software which has been developed to operate MCDB. The main purpose of the LCG MCDB project is to provide a storage and documentation system for sophisticated event samples simulated for the LHC collaborations by experts. In many cases, the modern Monte Carlo simulation of physical processes requires expert knowledge in Monte Carlo generators or significant amount of CPU time to produce the events. MCDB is a knowledgebase mainly dedicated to accumulate simulated events of this type. The main motivation behind LCG MCDB is to make the sophisticated MC event samples available for various physical groups. All the data from MCDB is accessible in several convenient ways. LCG MCDB is being developed within the CERN LCG Application Area Simulation project

Higgs boson production under the resonance threshold at LEP II

We consider the possibility of Higgs boson detection at LEP II under the resonance threshold ($\sqrt{s}<m_H+m_Z$) in the framework of complete tree level approach to the calculation of the $e^+ e^- \rightarrow \nu \bar \nu b \bar b$ amplitude, simulating b-quark fragmentation to hadrons and taking into account typical detector properties. At the energy below the $2m_Z$ threshold $\sqrt{s}=$ 175 GeV Higgs boson production under the $m_H+m_Z$ threshold is practically background free.Comment: 19 pages, including 1 figure in LaTeX, 8 postscript figure

Light and Intermediate Higgs boson search at Tevatron Energies

We study the Higgs boson search possibility at the TEVATRON energies. The detailed analysis of the 4-fermion final state reactions is presented. Among the complete set of Feynman diagrams the main contribution to the final states comes from the Higgs signal WH and ZH, from the backgrounds WZ, ZZ and gluonic background Wbb, Zbb with subssiquent decays of W, Z bosons. It is shown that the important contribution to the background is connected with single top quark production subreactions qq-bar --> tb-bar or t-bar b with the top decay to Wb. As a result of various distributions for Higgs signal and backgrounds a number of optimum cuts has been found. The finaleffective $b\bar{b}$ -- pair mass distribution allows to extract the signal from Higgs with mass up to about 100 GeV at 2 TeV C.M. energy and up to about 120 GeV at 4 TeV C.M. energy for the integrated luminosity 1000 inverse pb.Comment: 18 pages including 8 figures as 9 gzipped and uuencoded postscript file