Publications

High-energy physics experiments rely on reconstruction of the trajectories of particles produced at the interaction point. This is a challenging task, especially in the high track multiplicity environment generated by p-p collisions at the LHC energies. A typical event includes hundreds of signal examples (interesting decays) and a significant amount of noise (uninteresting examples). This work describes a modification of the Artificial Retina algorithm for fast track finding: numerical optimization methods were adopted for fast local track search. This approach allows for considerable reduction of the total computational time per event. Test results on simplified simulated model of LHCb VELO (VErtex LOcator) detector are presented. Also this approach is well-suited for implementation of paralleled computations as GPGPU which look very attractive in the context of upcoming detector upgrades.

The oscillation frequency, TeV">TeVTeV. A combination of the two decay modes gives <span data-mathml="nsΔmd=(505.0±2.1±1.0)ns−1Δmd=(505.0±2.1±1.0)ns−1, where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.

This paper aims to tackle the problem of brain network classification with machine learning algorithms using spectra of networks' matrices. Two approaches are discussed: first, linear and tree-based models are trained on the vectors of sorted eigenvalues of the adjacency matrix, the Laplacian matrix and the normalized Laplacian; next, SVM classifier is trained with kernels based on information divergence between the eigenvalue distributions. The latter approach gives promising results in the classification of autism spectrum disorder versus typical development and of the carriers versus noncarriers of an allele associated with the high risk of Alzheimer disease.

A search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W−p(*) →p(*)μ±e∓p(*) at s√=8s=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb−1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e∓) > 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 fb−1 of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 ± 0.6 (0.84 ± 0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive γγ → W+W− production. Upper limits on the anomalous quartic gauge coupling operators a0,CW (dimension-6) andfM0,1,2,3 (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.

A full amplitude analysis of Λ 0 b → J/ψ pπ− decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb−1 . A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations N → pπ−, either the Pc(4380)+ and Pc(4450)+ → J/ψ p states, previously observed in Λ 0 b → J/ψ pK− decays, or the Zc(4200)− → J/ψ π− state, previously reported in B0 → J/ψ K+π − decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the Pc(4380)+ and Pc(4450)+ production rates expected from their previous observation taking account of Cabibbo suppression.

Charm meson oscillations are observed in a time-dependent analysis of the ratio of D0 → K+π −π +π − to D0 → K−π +π −π + decay rates, using data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes r K3π D and the product of the coherence factor RK3π D and a charm mixing parameter y 0 K3π . The constraints measured are r K3π D = (5.67±0.12)×10−2 , which is the most precise determination to date, and RK3π D · y 0 K3π = (0.3 ± 1.8) × 10−3 , which provides useful input for determinations of the CP-violating phase γ in B±→ DK±, D→ K∓π ±π ∓π ± decays. The analysis also gives the most precise measurement of the D0 → K+π −π +π − branching fraction, and the first observation of D0–D0 oscillations in this decay mode, with a significance of 8.2 standard deviations.

A time-dependent angular analysis of Bs0→ψ(2S)ϕ decays is performed using data recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0fb−1 collected during Run 1 of the LHC. The CP -violating phase and decay-width difference of the Bs0 system are measured to be ϕs=0.23−0.28+0.29±0.02rad and ΔΓs=0.066−0.044+0.041±0.007ps−1 , respectively, where the first uncertainty is statistical and the second systematic. This is the first time that ϕs and ΔΓs have been measured in a decay containing the ψ(2S) resonance.

Identifying the flavour of neutral B mesons production is one of the most important components needed in the study of time-dependent CP violation. The harsh environment of the Large Hadron Collider makes it particularly hard to succeed in this task. We present an inclusive flavour-tagging algorithm as an upgrade of the algorithms currently used by the LHCb experiment. Specifically, a probabilistic model which efficiently combines information from reconstructed vertices and tracks using machine learning is proposed. The algorithm does not use information about underlying physics process. It reduces the dependence on the performance of lower level identification capacities and thus increases the overall performance. The proposed inclusive flavour-tagging algorithm is applicable to tag the flavour of B mesons in any proton-proton experiment.

The influence of ringing effect (which is based on the Gibbs phenomenon) on the mutual coherence in sparse representation approach is considered. It is shown that for random vectors, the ringing effect increases the average mutual coherence. Numerical results that demonstrate that the mutual coherence behaves identically for real images are given. It is also shown how the ringing effect affects the sparsity of representations (which is closely related to the mutual coherence).

A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2TeVTeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8TeVTeV corresponding to an integrated luminosity of 19.7fb−1fb−1. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.

The production of W and Z bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 ± 0.02 fb−1 . The W boson is identified using its decay to a muon and a neutrino, while the Z boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of W+jet and Z+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

A measurement of the cross-section for W → eν production in pp collisions is presented using data corresponding to an integrated luminosity of 2 fb−1 collected by the LHCb experiment at a centre-of-mass energy of √ s = 8 TeV. The electrons are required to have more than 20 GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive W production cross-sections, where the W decays to eν, are measured to be σW+→e+νe = 1124.4 ± 2.1 ± 21.5 ± 11.2 ± 13.0 pb, σW−→e−νe = 809.0 ± 1.9 ± 18.1 ± 7.0 ± 9.4 pb, where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. Differential cross-sections as a function of the electron pseudorapidity are measured. The W+/W− cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of W boson branching fractions is determined to be B(W → eν)/B(W → µν) = 1.020 ± 0.002 ± 0.019, where the first uncertainty is statistical and the second is systematic

The differential cross section and charge asymmetry for inclusive pp→W±+X→μ±ν+Xpp→W±+X→μ±ν+Xproduction at s√=8TeVs=8TeV are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8fb−1fb−1 recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10−310−3 to 10−110−1.