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.
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.
A new method for simulating electroweak top-quark production processes is described along with its computer realization in the SingleTop event generator. Special attention is paid to the correct ...combination of events from two parts of the main t-channel production process: 2 → 2 with a b quark in the initial state and 2 → 3, where an additional b quark appears in the final state. Integration of these two contributions enables the generation of event samples including the first correction to the leading perturbation order, avoiding the double-counting problem and negative-weight events. The SingleTop generator is based on the complete set of the tree Feynman diagrams calculated by the CompHEP package.
The results of searches for effects beyond the Standard Model in processes of single top-quark production in the CMS experiment are presented. Anomalous contributions of the vector and magnetic types ...in top-quark interaction with the
W
boson and
b
quark and quark-flavor-changing neutral currents in top-quark interaction with the
c
or
u
quark via gluon exchange were studied. The respective analysis was performed with the aid of Bayesian neural networks. No statistically significant deviations were found, and upper limits on anomalous couplings at a 95% confidence level were set.
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