arXiv subjects
Publications and source records attributed to L. Dudko.
We present a new version of the CompHEP program package, version 4.5. We describe new options and techniques implemented in the version: interfaces to ROOT and HERWIG, parallel calculations, generation of the XML-based header in event files (HepML), full implementation of the Les Houches agreements (LHA I, SUSY LHA, LHA PDF, Les Houches Event format), cascade matching for intermediate scalar resonances, etc.
We present a collection of signatures for physics beyond the standard model that need to be explored at the LHC. The signatures are organized according to the experimental objects that appear in the final state, and in particular the number of high pT leptons. Our report, which includes brief experimental and theoretical reviews as well as original results, summarizes the activities of the "New Physics'' working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 11-29 June, 2007).
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.
We propose to combine and slightly extend two existing "Les Houches Accords" to provide a simple generic interface between beyond-the-standard-model parton-level and event-level generators. All relevant information - particle content, quantum numbers of new states, masses, cross sections, parton-level events, etc - is collected in one single file, which adheres to the Les Houches Event File (LHEF) standard.
The paper is devoted to studies of prospects to search for hypothetical W-prime gauge bosons at hadron colliders via single-top quark production process. A special attention is paid to the interference between the Standard Model (SM) W and W-prime} boson contributions. A model independent analysis is performed for a wide interval of W-prime} masses potentially acceptable for a detection at the Tevatron and LHC. It is shown that the interference contribution to the cross section of the most promising s-channel single top production mode could be as large as 30 % for certain parameter points which is comparable to NLO effects computed in previous studies separately for the W-prime signal and the SM single-top background. The interference contribution affects particle distributions and has to be taken into account for more accurate W-prime signal and background simulation.
A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.
The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as computational tools designed in order to facilitate their phenomenology.
Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed.
We present the Monte-Carlo events Data Base (MCDB) project and its development plans. MCDB facilitates communication between authors of Monte-Carlo generators and experimental users. It also provides a convenient book-keeping and an easy access to generator level samples. The first release of MCDB is now operational for the CMS collaboration. In this paper we review the main ideas behind MCDB and discuss future plans to develop this Data Base further within the CERN LCG framework.
We present a new version of the CompHEP program (version 4.4). We describe shortly new issues implemented in this version, namely, simplification of quark flavor combinatorics for the evaluation of hadronic processes, Les Houches Accord based CompHEP-PYTHIA interface, processing the color configurations of events, implementation of MSSM, symbolical and numerical batch modes, etc. We discuss how the CompHEP program is used for preparing event generators for various physical processes. We mention a few concrete physics examples for CompHEP based generators prepared for the LHC and Tevatron.
This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.
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.
Search for single top quark and Higgs boson production is among the main goals for the upgraded Tevatron. We study the feasibility of single top quark and Higgs boson search at Tevatron both together since these processes have very similar final state signatures and so backgrounds. Calculation of the cross sections and a detailed analysis of various kinematic distributions for signal and for main backgrounds has been performed. As a result of this study an opimized set of cuts has been worked out for background suppression and for extraction of the signal. This study gives proof to the possibility of testing the nature of the {\wtb} coupling and of a direct measurement of the {\vtb} CKM parameter. The \bbbar -- pair effective mass distribution study allows to extract the signal of Higgs with mass up to about $100\gev$ at $\sqs = 2\tev$ and up to about $120\gev$ at $\sqs = 4\tev$ for integrated luminosity $L= 1000\ipb$.
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 $e^+ e^- \rightarrow ν\bar νb \bar b$ 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.
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.