Mihail V. Chizhov

Bio: Mihail V. Chizhov is an academic researcher from Sofia University. The author has contributed to research in topics: Large Hadron Collider & Boson. The author has an hindex of 4, co-authored 15 publications receiving 51 citations. Previous affiliations of Mihail V. Chizhov include Joint Institute for Nuclear Research.

Search for doubly and singly charged Higgs bosons decaying into vector bosons in multi-lepton final states with the ATLAS detector using proton-proton collisions at √s = 13 TeV

Abstract: A search for charged Higgs bosons decaying into W±W± or W±Z bosons is performed, involving experimental signatures with two leptons of the same charge, or three or four leptons with a variety of charge combinations, missing transverse momentum and jets. A data sample of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb−1. The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged H±± bosons, or the associated production of a doubly charged H±± boson and a singly charged H± boson. No significant deviations from the Standard Model predictions are observed. H±± bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively. [Figure not available: see fulltext.]

Search for new phenomena in final states with b-jets and missing transverse momentum in √s = 13 TeV pp collisions with the ATLAS detector

Abstract: The results of a search for new phenomena in final states with b-jets and missing transverse momentum using 139 fb−1 of proton-proton data collected at a centre-of-mass energy $$ \sqrt{s} $$ = 13 TeV by the ATLAS detector at the LHC are reported The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously

Determination of the parton distribution functions of the proton from ATLAS measurements of differential W± and Z boson production in association with jets

Abstract: This article presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of $W^+$ and $W^-$ boson and $Z$ boson production in association with jets in $pp$ collisions at $\sqrt{s} = 8~\mathrm{TeV}$ performed by the ATLAS experiment at the LHC with integrated luminosities of $20.2~\mathrm{fb}^{-1}$ and $19.9~\mathrm{fb}^{-1}$, respectively. The analysis also considers the ATLAS measurements of differential $W^{\pm}$ and $Z$ boson production at $\sqrt{s} = 7~\mathrm{TeV}$ with an integrated luminosity of $4.6~\mathrm{fb}^{-1}$ and deep-inelastic-scattering data from $e^{\pm}p$ collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken $x$ is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range $x \lesssim 0.02$ found by previous ATLAS analyses.

Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS

Abstract: Two-particle long-range azimuthal correlations are measured in photonuclear collisions using 1.7 nb$^{-1}$ of 5.02 TeV Pb+Pb collision data collected by the ATLAS experiment at the LHC. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle correlation functions are formed using charged-particle tracks in the selected events, and a template-fitting method is employed to subtract the non-flow contribution to the correlation. Significant nonzero values of the second- and third-order flow coefficients are observed and presented as a function of charged-particle multiplicity and transverse momentum. The results are compared with flow coefficients obtained in proton-proton and proton-lead collisions in similar multiplicity ranges, and with theoretical expectations. The unique initial conditions present in this measurement provide a new way to probe the origin of the collective signatures previously observed only in hadronic collisions.

Sensitivity to new physics: a_e vs. a_mu

Abstract: At present it is generally believed that ``new physics'' effects contribute to leptonic anomalous magnetic moment, a_l, via quantum loops only and they are proportional to the squared lepton mass, (m_l)^2. An alternative mechanism for a contribution by new physics is proposed. It occurs at the tree level and exhibits a linear rather than quadratic dependence on m_l. This leads to a much larger sensitivity of a_e to the new physics than was expected so far.

A Schematic Model of Baryons and Mesons

Abstract: If we assume that the strong interactions of baryons and mesons are correctly described in terms of the broken "eightfold way", we are tempted to look for some fundamental explanation of the situation. A highly promised approach is the purely dynamical "bootstrap" model for all the strongly interacting particles within which one may try to derive isotopic spin and strangeness conservation and broken eightfold symmetry from self-consistency alone. Of course, with only strong interactions, the orientation of the asymmetry in the unitary space cannot be specified; one hopes that in some way the selection of specific components of the F-spin by electromagnetism and the weak interactions determines the choice of isotopic spin and hypercharge directions.

Kaon Decays in the Standard Model

Abstract: A comprehensive overview of kaon decays is presented The standard model predictions are discussed in detail, covering both the underlying short-distance electroweak dynamics and the important interplay of QCD at long distances Chiral perturbation theory provides a universal framework for treating leptonic, semileptonic, and nonleptonic decays including rare and radiative modes All allowed decay modes with branching ratios of at least ${10}^{\ensuremath{-}11}$ are analyzed Some decays with even smaller rates are also included Decays that are strictly forbidden in the standard model are not considered in this review The present experimental status and the prospects for future improvements are reviewed

The Forward Physics Facility at the High-Luminosity LHC

Abstract: High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF’s physics potential.

The PDF4LHC21 combination of global PDF fits for the LHC Run III*

Abstract: A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton–hadron and hadron–hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin of the differences between the three global PDF sets. In particular, dedicated fits based on almost identical theory settings and input datasets are performed by the three groups, highlighting the role played by the respective fitting methodologies. We compare the new PDF4LHC21 combination with its predecessor, PDF4LHC15, demonstrating their good overall consistency and a modest reduction of PDF uncertainties for key LHC processes such as electroweak gauge boson production and Higgs boson production in gluon fusion. We study the phenomenological implications of PDF4LHC21 for a representative selection of inclusive, fiducial, and differential cross sections at the LHC. The PDF4LHC21 combination is made available via the LHAPDF library and provides a robust, user-friendly, and efficient method to estimate the PDF uncertainties associated to theoretical calculations for the upcoming Run III of the LHC and beyond.

Searching for leptoquarks at future muon colliders

Abstract: A high energy muon collider can provide new and complementary discovery potential to the LHC or future hadron colliders. Leptoquarks are a motivated class of exotic new physics models, with distinct production channels at hadron and lepton machines. We study a vector leptoquark model at a muon collider with $\sqrt{s} = 3, 14$ TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe leptoquark masses up to an order of magnitude beyond $\sqrt{s}$ with perturbative couplings. Additionally, we can also probe regions of parameter space unavailable to flavor experiments. In particular, all of the parameter space of interest to explain recent low-energy anomalies in B meson decays would be covered even by a $\sqrt{s} = 3$ TeV collider.