Персона: Тихомиров, Владимир Олегович
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Институт ядерной физики и технологий
Цель ИЯФиТ и стратегия развития - создание и развитие научно-образовательного центра мирового уровня в области ядерной физики и технологий, радиационного материаловедения, физики элементарных частиц, астрофизики и космофизики.
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Владимир Олегович
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- ПубликацияТолько метаданныеMeasurement of angular and momentum distributions of charged particles within and around jets in Pb plus Pb and pp collisions at root s(NN)=5.02 TeV with ATLAS at the LHC(2019) Puri, A.; Aaboud, M.; Aad, G.; Abbott, B.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Shulga, E.; Smimov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин АлександровичStudies of the fragmentation of jets into charged particles in heavy-ion collisions can help in understanding the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. These proceedings present a measurement of the angular distribution of charged particles around the jet axis in root s(NN) = 5.02 TeV Pb+Pb and pp collisions, done using the ATLAS detector at the LHC. The measurement is performed inside jets reconstructed with the anti-k(t) algorithm with radius parameter R = 0.4, and is extended to regions outside the jet cone. Results are presented as a function of Pb+Pb collision centrality, and both jet and charged-particle transverse momenta.
- ПубликацияТолько метаданныеMeasurement of flow harmonics correlations with mean transverse momentum in lead–lead and proton–lead collisions at √sNN=5.02TeV with the ATLAS detector(2019) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Timoshenko, S.; Vorobev, K.; Tikhomirov, V. O.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович; Тихомиров, Владимир Олегович© 2019, CERN for the benefit of the ATLAS collaboration.To assess the properties of the quark–gluon plasma formed in ultrarelativistic ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the flow harmonics. The analysis uses data samples of lead–lead and proton–lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02 TeV, corresponding to total integrated luminosities of 22μb-1 and 28nb-1, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the 2nd-, 3rd-, and 4th-order flow harmonics are measured in the lead–lead collisions as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution, which only weakly depends on the charged-particle momentum range. In the proton–lead collisions, the modified Pearson correlation coefficient measured for the 2nd-order flow harmonics shows only weak centrality dependence. The lead-lead data is qualitatively described by the predictions based on the hydrodynamical model.
- ПубликацияТолько метаданныеMeasurement of KS0 and Λ production in tt¯ dileptonic events in pp collisions at √s= 7 TeV with the ATLAS detector(2019) Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович© 2019, CERN for the benefit of the ATLAS collaboration.Measurements of KS0 and Λ production in tt¯ final states have been performed. They are based on a data sample with integrated luminosity of 4.6 fb - 1 from proton–proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tt¯ dileptonic events is found to be well described by current Monte Carlo models for KS0 and Λ production within jets, but not for those produced outside jets.
- ПубликацияТолько метаданныеMeasurement of the flow harmonic correlations in pp, p plus Pb and low multiplicity Pb plus Pb collisions with the ATLAS detector at the LHC(2019) Derendarz, D.; Aaboud, M.; Aad, G.; Abbott, B.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Shulga, E.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин АлександровичRecent measurements of the correlations between flow harmonics obtained using four-particle symmetric cumulants and three-particle asymmetric cumulants with the ATLAS detector at the LHC are described. The data sets of pp, p+Pb and peripheral Pb+Pb collisions at various energies are analyzed, aiming to probe the long-range collective nature of multi-particle production in small systems. The sensitivity of the standard cumulant method to non-flow correlations is investigated by introducing the subevents method. A systematic reduction of non-flow effects is observed when using the two-subevent method. Further reduction is observed with the three-subevent method that is consistent with the results obtained with the four-subevent one. A negative correlation between v(2) and v(3) and a positive correlation between v(2) and v(4), for all studied collision systems and over full multiplicity range, is observed. The correlation strength computed as symmetric cumulants normalized by the < v(n)(2)> is similar for all collision systems and weakly depends on multiplicity. These measurements provide new evidence for long-range multi-particle collectivity in small collision systems and quantify the nature of its event-by-event fluctuations.
- ПубликацияТолько метаданныеCharged-hadron suppression in Pb plus Pb and Xe plus Xe collisions measured with the ATLAS detector(2019) Balek, P.; Aaboud, M.; Aad, G.; Abbott, B.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Shulga, E.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин АлександровичThe ATLAS detector at the LHC recorded 0.49 nb(-1) of Pb+Pb collisions and 25 of pp(-1) collisions, both at the center-of-mass energy 5.02 TeV per nucleon pair. Recently, ATLAS also recorded 30 mu b(-1) of Xe+Xe collisions at the center-of-mass energy 5.44 TeV, which provides a new opportunity to study the system-size dependence of the charged-hadron production in heavy-ion collisions. The large acceptance of the ATLAS detector allows to measure the spectra of charged hadrons in a wide range of pseudorapidity and transverse momentum. The nuclear modification factors R-AA are constructed as a ratio of the spectra measured in Pb+Pb or Xe+Xe collisions to that measured in pp collisions. The R-AA obtained in the two systems are presented for different centrality intervals and the results are discussed.
- ПубликацияТолько метаданныеPerformance of the ATLAS muon triggers in Run 2(2020) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин АлександровичThe performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015-2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons to cover the intermediate momentum range between 26 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68% in the barrel region and 85% in the endcap region. The p(T) range for efficiency determination is extended by using muons from decays of J/psi mesons, W bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in pp collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail.
- ПубликацияТолько метаданныеSearch for direct production of electroweakinos in final states with missing transverse momentum and a Higgs boson decaying into photons in pp collisions at √s = 13 TeV with the ATLAS detector(2020) Aad, G.; Abbott, B.; Abbott, D. C.; Abed, Abud, A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kantserov, V. A.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович© 2020, The Author(s).A search for a chargino-neutralino pair decaying via the 125 GeV Higgs boson into photons is presented. The study is based on the data collected between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb−1 of pp collisions at a centre-of-mass energy of 13 TeV. No significant excess over the expected background is observed. Upper limits at 95% confidence level for a massless χ˜10 are set on several electroweakino production cross-sections and the visible cross-section for beyond the Standard Model processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 310 GeV in m(χ˜1±/χ˜20), where m(χ˜10) = 0.5 GeV, are set. Limits at 95% confidence level are also set on the χ˜1±χ˜20 cross-section in the mass plane of m(χ˜1±/χ˜20) and m(χ˜10), and on scenarios with gravitino as the lightest supersymmetric particle. Upper limits at the 95% confidence-level are set on the higgsino production cross-section. Higgsino masses below 380 GeV are excluded for the case of the higgsino fully decaying into a Higgs boson and a gravitino. [Figure not available: see fulltext.]
- ПубликацияТолько метаданныеDijet Resonance Search with Weak Supervision Using root S=13 TeV pp Collisions in the ATLAS Detector(2020) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Pyatiizbyantseva, D.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович; Пятиизбянцева, Диана НиколаевнаThis Letter describes a search for narrowly resonant new physics using a machine -learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search A -> BC, for m(A) similar to O(TeV), m(B), m(C) similar to O(100 GeV) and B, C are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full run 2 root s = 13 TeV pp collision dataset of 139 fb(-1) recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV, Cross-section limits for narrow -width A, B, and C particles vary with m(A), m(B), and m(C). For example, when m(A) = 3 TeV and m(B) greater than or similar to 200 GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on m(C). For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search. These results are complementary to the dedicated searches for the case that B and C are standard model bosons.
- ПубликацияТолько метаданныеHiggs boson production cross-section measurements and their EFT interpretation in the 4 ℓ decay channel at √s= 13 TeV with the ATLAS detector(2020) Aad, G.; Abbott, B.; Abbott, D. C.; Abud, A. A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Pyatiizbyantseva, D.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Пятиизбянцева, Диана Николаевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович© 2020, The Author(s).Higgs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb - 1 of proton–proton collision data recorded at s=13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for H→ ZZ∗ decay is measured to be 1.34 ± 0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of 1.33 ± 0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.
- ПубликацияТолько метаданныеMeasurement of the tt¯ production cross-section in the lepton+jets channel at s=13 TeV with the ATLAS experiment(2020) Aad, G.; Abbott, B.; Abbott, D. C.; Abed, Abud, A.; Belotskiy, K.; Belyaev, N. L.; Bulekov, O.; Kurova, A.; Ponomarenko, D.; Proklova, N.; Pyatiizbyantseva, D.; Romaniouk, A.; Smirnov, N.; Smirnov, S. Y.; Smirnov, Y.; Soldatov, E. Y.; Tikhomirov, V. O.; Timoshenko, S.; Vorobev, K.; Белоцкий, Константин Михайлович; Булеков, Олег Владимирович; Курова, Анастасия Сергеевна; Пятиизбянцева, Диана Николаевна; Романюк, Анатолий Самсонович; Смирнов, Сергей Юрьевич; Смирнов, Юрий Сергеевич; Солдатов, Евгений Юрьевич; Тихомиров, Владимир Олегович; Тимошенко, Сергей Леонидович; Воробьёв, Константин Александрович© 2020 The Author(s)The top anti-top quark production cross-section is measured in the lepton+jets channel using proton–proton collision data at a centre-of-mass energy of s=13 TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb−1. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing b-hadrons, are used to determine the tt¯ production cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be σinc=830±0.4(stat.)±36(syst.)±14(lumi.)pb with a relative uncertainty of 4.6%. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD. The fiducial tt¯ cross-section within the experimental acceptance is also measured.