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

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

CompHEP 4.4 - Automatic Computations from Lagrangians to Events

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.Comment: The paper has been presented on IX International Workshop on Advanced Computing and Analysis Techniques in Physics Research December 1-5, 2003. KEK, Japan. 10 pages, 2 figure

Fifth-neighbor spin-spin correlator for the anti-ferromagnetic Heisenberg chain

We study the generating function of the spin-spin correlation functions in the ground state of the anti-ferromagnetic spin-1/2 Heisenberg chain without magnetic field. We have found its fundamental functional relations from those for general correlation functions, which originate in the quantum Knizhink-Zamolodchikov equation. Using these relations, we have calculated the explicit form of the generating functions up to n=6. Accordingly we could obtain the spin-spin correlator up to k=5.Comment: 10 page

Is there the radion in the RS2 model ?

We analyse the physical boundary conditions at infinity for metric fluctuations and gauge functions in the RS2 model with matter on the brane. We argue that due to these boundary conditions the radion field cannot be gauged out in this case. Thus, it represents a physical degree of freedom of the model.Comment: 9 page

The n-body problem in General Relativity up to the second post-Newtonian order from perturbative field theory

Motivated by experimental probes of general relativity, we adopt methods from perturbative (quantum) field theory to compute, up to certain integrals, the effective lagrangian for its n-body problem. Perturbation theory is performed about a background Minkowski spacetime to O[(v/c)^4] beyond Newtonian gravity, where v is the typical speed of these n particles in their center of energy frame. For the specific case of the 2 body problem, the major efforts underway to measure gravitational waves produced by in-spiraling compact astrophysical binaries require their gravitational interactions to be computed beyond the currently known O[(v/c)^7]. We argue that such higher order post-Newtonian calculations must be automated for these field theoretic methods to be applied successfully to achieve this goal. In view of this, we outline an algorithm that would in principle generate the relevant Feynman diagrams to an arbitrary order in v/c and take steps to develop the necessary software. The Feynman diagrams contributing to the n-body effective action at O[(v/c)^6] beyond Newton are derived.Comment: 39 pages. The Mathematica code used in this paper can be found at http://www.stargazing.net/yizen/PN.html Version 2: Slight re-wording of section on removal of accelerations in 2 PN lagrangian; comments added in conclusion; and typographical errors fixed. Article is similar to that published in PR

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

Probing the topcolor-assisted technicolor model via the single t-quark production at Hadron colliders

In this paper, we systematically study the contribution of the TC2 model to the single t-quark production at the Hadron colliders, specially at the LHC. The TC2 model can contribute to the cross section of the single t-quark production in two different ways. First, the existence of the top-pions and top-higgs can modify the $Wtb$ coupling via their loop contributions, and such modification can cause the correction to the cross sections of all three production modes. Our study shows that this kind of correction is negative and very small in all cases. Thus it is difficult to observe such correction even at the LHC. On the other hand, there exist the tree-level FC couplings in the TC2 model which can also contribute to the cross sections of the $tq$ and $t\bar{b}$ production processes. The resonant effect can greatly enhance the cross sections of the $tq$ and $t\bar{b}$ productions. The first evidence of the single t-quark production has been reported by the $D0$ collaboration and the measured cross section for the single t-quark production of $\sigma(p\bar{p}\to tb+X,tqb+X)$ is compatible at the 10% level with the standard model prediction. Because the light top-pion can make great contribution to the $t\bar{b}$ production, the top-pion mass should be very large in order to make the predicted cross section in the TC2 model be consistent with the Tevatron experiments. More detailed information about the top-pion mass and the FC couplings in the TC2 model should be obtained with the running of the LHC.Comment: 30 pages, 3 tables, 10 figure

Exact evaluation of density matrix elements for the Heisenberg chain

We have obtained all the density matrix elements on six lattice sites for the spin-1/2 Heisenberg chain via the algebraic method based on the quantum Knizhnik-Zamolodchikov equations. Several interesting correlation functions, such as chiral correlation functions, dimer-dimer correlation functions, etc... have been analytically evaluated. Furthermore we have calculated all the eigenvalues of the density matrix and analyze the eigenvalue-distribution. As a result the exact von Neumann entropy for the reduced density matrix on six lattice sites has been obtained.Comment: 33 pages, 4 eps figures, 3 author