CompHEP 4.4—automatic computations from Lagrangians to events Boos, E.; Bunichev, V.; Dubinin, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2004, Volume:
534, Issue:
1
Journal Article
Peer reviewed
Open access
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.
Methods for the application of neural networks in searches for new physics in collider experiments are described. Mechanisms of selecting observables, optimizing hyperparameters, and constructing ...cascades of deep neural networks are considered. Methods for a statistical analysis of neural-network discriminants in theta and CombinedLimit packages with allowance for various uncertainties are presented.
The Effective Field Theory (EFT) approach is widely used in the search for possible deviations from the predictions of the Standard Model. Such an approximation of possible BSM physics is valid up to ...a certain levels of energy scale and accuracy. In this article, we investigate potential limitation of the EFT approach related to unitarity to describe possible contributions of flavor-changing neutral currents (FCNC) involving the top quark. The numerical and analytical calculations of the FCNC processes used in the EFT approach demonstrate the constant asymptotic behavior of the total cross section with increasing energy. It is shown that the EFT approach for studying the possible contribution of FCNC does not violate the restrictions following from perturbative unitarity, the asymptotic behavior of the cross section does not exceed the Froissart bound, and the approach itself can be used to set the corresponding experimental limits for FCNC couplings or Wilson coefficients at present and future colliders.
Modeling of the pair and single top quark production are discussed in the context of searches for the anomalous
couplings. For the simulation of the anomalous
couplings in the top quark production ...and/or decay, the Subsidiary Fields method allows to generate a minimal number of event samples to cover all possible values of the couplings. In the paper the Subsidiary Fields method is applied to simulate the full
process with
final state including the subsequent top quark and
boson decays. Correctness of the differential cross sections for arbitrary values of the
couplings is demonstrated for the case of the simultaneous presence of the left- and right-handed vector operators in the Wtb vertex.
Numerical simulations of processes of three and four top quark hadroproduction are carried out in the SMEFT model framework. The simulated data are used to derive theoretical constraints on Wilson ...coefficients of relevant SMEFT operators of dimension six. Obtained limits for both cases are discussed and compared in terms of processes sensitivity to possible BSM contribution. Results show that operators
and
are better constrained by the process of triple top production, whereas for operator
more accurate limits are obtained from the production of four top quarks. The last considered operator
is relatively loosely constrained by both processes.
Recent advancements in model-independent approaches in high energy physics have encountered challenges due to the limited effectiveness of unsupervised algorithms when compared to their supervised ...counterparts. In this paper, we present a novel approach utilizing a one-class deep neural network (DNN) to achieve accuracy levels comparable to supervised learning methods. Our proposed novelty detection algorithm uses a multilayer perceptron to learn and distinguish a specific class from simulated noise signals. By training on a single class, our algorithm constructs a hyperplane similar to one-class support vector machines (SVMs) but with enhanced accuracy and significantly reduced training and inference times. This research contributes to the advancement of model-independent techniques for uncovering New Physics phenomena, showcasing the potential of one-class DNNs as a viable alternative to traditional supervised learning approaches. For the demonstration of the method, the distinguishing of flavour changing neutral currents in top quark interactions from the Standard Model processes has been considered. The obtained results demonstrate the effectiveness of our proposed algorithm, paving the way for improved anomaly detection and exploration of uncharted territories in high energy physics.
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 paper presents a method for separating contributions of pair and single top quark production to tWb associated final state using a neural network. The proposed method makes it possible to ...calculate such processes in a gauge-invariant way, taking into account interference contributions and dividing the phase space into single-resonant and double-resonant regions. The optimized set of observables is used to separate single-resonant and double-resonant contributions to the overall process for neural network training. A usage of the method allows for avoiding the disadvantages that are inherent in the schemes used in collider physics for calculation of the tWb associated top quark production with the removal of Feynman diagrams, which leads to violation of gauge invariance, or the addition of a subtraction scheme, which leads to the appearance of negative weights for the part of simulated events. The proposed method can be used to increase the efficiency of the search for deviations from the predictions of the Standard Model in the interaction of the top quark with the W boson and b-quark.
In this paper we describe a HepML format and a corresponding C++ library developed for keeping complete description of parton level events in a unified and flexible form. HepML tags contain enough ...information to understand what kind of physics the simulated events describe and how the events have been prepared. A HepML block can be included into event files in the LHEF format. The structure of the HepML block is described by means of several XML Schemas. The Schemas define necessary information for the HepML block and how this information should be located within the block. The library
libhepml is a C++ library intended for parsing and serialization of HepML tags, and representing the HepML block in computer memory. The library is an API for external software. For example, Matrix Element Monte Carlo event generators can use the library for preparing and writing a header of an LHEF file in the form of HepML tags. In turn, Showering and Hadronization event generators can parse the HepML header and get the information in the form of C++ classes.
libhepml can be used in C++, C, and Fortran programs. All necessary parts of HepML have been prepared and we present the project to the HEP community.
Program title: libhepml
Catalogue identifier: AEGL_v1_0
Program summary URL:
http://cpc.cs.qub.ac.uk/summaries/AEGL_v1_0.html
Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland
Licensing provisions: GNU GPLv3
No. of lines in distributed program, including test data, etc.: 138 866
No. of bytes in distributed program, including test data, etc.: 613 122
Distribution format: tar.gz
Programming language: C++, C
Computer: PCs and workstations
Operating system: Scientific Linux CERN 4/5, Ubuntu 9.10
RAM: 1 073 741 824 bytes (1 Gb)
Classification: 6.2, 11.1, 11.2
External routines: Xerces XML library (
http://xerces.apache.org/xerces-c/), Expat XML Parser (
http://expat.sourceforge.net/)
Nature of problem: Monte Carlo simulation in high energy physics is divided into several stages. Various programs exist for these stages. In this article we are interested in interfacing different Monte Carlo event generators via data files, in particular, Matrix Element (ME) generators and Showering and Hadronization (SH) generators. There is a widely accepted format for data files for such interfaces – Les Houches Event Format (LHEF). Although information kept in an LHEF file is enough for proper working of SH generators, it is insufficient for understanding how events in the LHEF file have been prepared and which physical model has been applied. In this paper we propose an extension of the format for keeping additional information available in generators. We propose to add a new information block, marked up with XML tags, to the LHEF file. This block describes events in the file in more detail. In particular, it stores information about a physical model, kinematical cuts, generator, etc. This helps to make LHEF files self-documented. Certainly, HepML can be applied in more general context, not in LHEF files only.
Solution method: In order to overcome drawbacks of the original LHEF accord we propose to add a new information block of HepML tags. HepML is an XML-based markup language. We designed several XML Schemas for all tags in the language. Any HepML document should follow rules of the Schemas. The language is equipped with a library for operation with HepML tags and documents. This C++ library, called
libhepml, consists of classes for HepML objects, which represent a HepML document in computer memory, parsing classes, serializating classes, and some auxiliary classes.
Restrictions: The software is adapted for solving problems, described in the article. There are no additional restrictions.
Running time: Tests have been done on a computer with Intel(R) Core(TM)2 Solo, 1.4 GHz. Parsing of a HepML file: 6 ms (size of the HepML files is 12.5 Kb) Writing of a HepML block to file: 14 ms (file size 12.5 Kb) Merging of two HepML blocks and writing to file: 18 ms (file size – 25.0 Kb).
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