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Adamczyk, L.

Publications and source records attributed to Adamczyk, L..

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Measurement of the Higgs boson coupling properties in the H → ZZ * → 4ℓ decay channel at $ \sqrt{s}=13 $ TeV with the ATLAS detector

Here, the coupling properties of the Higgs boson are studied in the four-lepton (e, μ) decay channel using 36.1 fb –1 of pp collision data from the LHC at a centre-of-mass energy of 13 TeV collected by the ATLAS detector. Cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for H → ZZ* decay and for a Higgs boson absolute rapidity below 2.5 is measured to be 1.73 –0.23 +0.24 (stat.) –0.08 +0.10 (exp.) ± 0.04(th.) pb compared to the Standard Model prediction of 1.34±0.09 pb. In addition, the tensor structure of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to Z bosons and on the CP-odd coupling to gluons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for doubly charged Higgs boson production in multi-lepton final states with the ATLAS detector using proton–proton collisions at $\sqrt{s}=13\,\text {TeV}$

In this paper, a search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton–proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to 36.1 fb –1 of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays H ±± → e ± e ± , H ±± → e ± μ ± and H ±± → μ ± μ ± , fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section and consequently a lower limit on m(H ±± ) are derived at 95% confidence level. With ℓ ± ℓ ± = e ± e ± /μ ± μ ± /e ± μ ± , the observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons varies from 770 to 870 GeV (850 GeV expected) for B(H ±± → ℓ ± ℓ ± )=100% and both the expected and observed mass limits are above 450 GeV for B(H ±± → ℓ ± ℓ ± )=10% and any combination of partial branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for W W/W Z resonance production in ℓνqq final states in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector

Here, a search is conducted for new resonances decaying into a W W or W Z boson pair, where one W boson decays leptonically and the other W or Z boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb –1 collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of √s = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector-boson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of differential cross-sections of a single top quark produced in association with a W boson at $\sqrt{s}={13}{\text {TeV}}$ with ATLAS

The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using 36.1fb -1 of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are then measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Searches for heavy ZZ and ZW resonances in the ℓℓqq and ννqq final states in pp collisions at $ \sqrt{s}=13 TeV$ with the ATLAS detector

This article reports searches for heavy resonances decaying into ZZ or ZW using data from proton-proton collisions at a centre-of-mass energy of $ \sqrt{s}=13 $ TeV. The data, corresponding to an integrated luminosity of 36.1 fb -1 , were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The searches are performed in final states in which one Z boson decays into either a pair of light charged leptons (electrons and muons) or a pair of neutrinos, and the associated W boson or the other Z boson decays hadronically. No evidence of the production of heavy resonances is observed. Upper bounds on the production cross sections of heavy resonances times their decay branching ratios to ZZ or ZW are derived in the mass range 300-5000GeV within the context of Standard Model extensions with additional Higgs bosons, a heavy vector triplet or warped extra dimensions. Production through gluon-gluon fusion, Drell-Yan or vector-boson fusion are considered, depending on the assumed model.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Search for heavy resonances decaying into a W or Z boson and a Higgs boson in final states with leptons and b -jets in 36 fb -1 of $ \sqrt{s}=13 $ TeV pp collisions with the ATLAS detector

Here, a search is conducted for new resonances decaying into a W or Z boson and a 125 GeV Higgs boson in the $v\bar{v}$$b\bar{b}$, ℓ ± ν$b\bar{b}$, and ℓ + ℓ - $b\bar{b}$ final states, where ℓ ± = e ± or μ ± , in pp collisions at $\sqrt{s}$ =13 TeV. The data used correspond to a total integrated luminosity of 36.1 fb -1 collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of W h and Zh candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy W' and Z' resonances in heavy-vector-triplet models and the CP-odd scalar boson A in two-Higgs-doublet models. Upper limits are placed at the 95% confidence level and range between 9.0 × 10 -4 pb and 7.3 × 10 -1 pb depending on the model and mass of the resonance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Measurement of quarkonium production in proton–lead and proton–proton collisions at $5.02~\mathrm {TeV}$ with the ATLAS detector

The modification of the production of J/ψ, ψ(2S), and Υ(nS) (n=1,2,3) in p+Pb collisions with respect to their production in pp collisions has been studied. The p+Pb and pp datasets used in this paper correspond to integrated luminosities of 28 nb –1 and 25 pb –1 respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of J/ψ and ψ(2S) are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, R pPb for J/ψ and Υ(nS). No significant modification of the J/ψ production is observed while Υ(nS) production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. In conclusion, the production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of $\tau$ polarisation in $Z/\gamma ^{*}\rightarrow\tau\tau$→decays in proton–proton collisions at $\sqrt{s}=8$ with the ATLAS detector

This article presents a measurement of the polarisation of τ leptons produced in Z/ γ * → ττ decays which is performed with a dataset of proton—proton collisions at $\sqrt{s}$=8 TeV, corresponding to an integrated luminosity of 20.2 fb -1 recorded with the ATLAS detector at the LHC in 2012. The Z/γ* → ττ decays are reconstructed from a hadronically decaying τ lepton with a single charged particle in the final state, accompanied by a τ lepton that decays leptonically. The τ polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic τ decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The τ polarisation extracted over the full phase space within the Z/γ* mass range of 66 < m Z/γ* < 116 GeV is found to be P τ = - 0.14 ± 0.02 (stat) ± 0.04 (syst). It is in agreement with the Standard Model prediction of P τ = - 0.1517 ± 0.0019 , which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA τ decay library.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for the direct production of charginos and neutralinos in final states with tau leptons in $\sqrt{s}$ =13 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with at least two hadronically decaying tau leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 36.1 fb -1 , recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of $ \tilde{X} $$ \mathbb +\atop{1}$$ \tilde{X}$$ \mathbb -\atop{1}$ pair production and of $ \tilde{X} $$ \mathbb ±\atop{1}$$ \tilde{X}$$ \mathbb 0\atop{2}$ and $ \tilde{X} $$ \mathbb +\atop{1}$$ \tilde{X}$$ \mathbb -\atop{1}$ production in simplified models where the neutralinos and charginos decay solely via intermediate left-handed staus and tau sneutrinos, and the mass of the $ \tilde{&tau;} $ L state is set to be halfway between the masses of the $ \tilde{X} $$ \mathbb ±\atop{1}$ and the $ \tilde{X}$$ \mathbb 0\atop{1}$. Chargino masses up to 630 GeV are excluded at 95% confidence level in the scenario of direct production of $ \tilde{X} $$ \mathbb +\atop{1}$$ \tilde{X}$$ \mathbb -\atop{1}$ for a massless $ \tilde{X}$$ \mathbb 0\atop{1}$. Common $ \tilde{X} $$ \mathbb ±\atop{1}$ and $ \tilde{X}$$ \mathbb 0\atop{2}$ masses up to 760 GeV are excluded in the case of production of $ \tilde{X} $$ \mathbb ±\atop{1}$$ \tilde{X}$$ \mathbb 0\atop{2}$ and $ \tilde{X} $$ \mathbb +\atop{1}$$ \tilde{X}$$ \mathbb -\atop{1}$ assuming a massless $ \tilde{X}$$ \mathbb 0\atop{1}$. Exclusion limits for additional benchmark scenarios with large and small mass-splitting between the$ \tilde{X} $$ \mathbb ±\atop{1}$ and the $ \tilde{X}$$ \mathbb 0\atop{1}$ are also studied by varying the $ \tilde{&tau;} $ L mass between the masses of the$ \tilde{X} $$ \mathbb ±\atop{1}$ and the $ \tilde{X}$$ \mathbb 0\atop{1}$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of longitudinal flow decorrelations in Pb+Pb collisions at $\sqrt{s_{\text {NN}}}=2.76$ and 5.02 TeV with the ATLAS detector

Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range |η|<2.4 using 7 and 470 μb -1 of Pb+Pb collisions at $\sqrt{s}$$_ {NN}$= 2.76 and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients v n measured in two separated η intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the η separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the kth-moment of the vn are found to be proportional to k for v 3 , but not for v 2 . The decorrelation effect is separated into contributions from the magnitude of v n and the event-plane orientation, each as a function of η. These two contributions are found to be comparable. The longitudinal flow correlations are also measured between v n of different order in n. The decorrelations of v 2 and v 3 are found to be independent of each other, while the decorrelations of v 4 and v 5 are found to be driven by the nonlinear contribution from v$2\atop{2}$ and v 2 v 3 , respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Direct top-quark decay width measurement in the $t\bar{t}$lepton+jets channel at $\sqrt{s}=8$s TeV with the ATLAS experiment

Here, this article presents a direct measurement of the decay width of the top quark using $t\bar{t}$ events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb -1 . The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, Γ t =1.76 ± 0.33 (stat.) $+0.79\atop{-0.68}$ (syst.) GeV for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Search for B-L R -parity-violating top squarks in $\sqrt{s}$=13TeV pp collisions with the ATLAS experiment

A search for direct pair production of top squarks in final states with two tau leptons, b -jets, and missing transverse momentum is presented. The analysis is based on proton-proton collision data at √s = 13 TeV corresponding to an integrated luminosity of 36.1 fb -1 recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Two exclusive channels with either two hadronically decaying tau leptons or one hadronically and one leptonically decaying tau lepton are considered. No significant deviation from the Standard Model predictions is observed in the data. The analysis results are interpreted in terms of model-independent limits and used to derive exclusion limits on the masses of the top squark $\tilde{t}_{1}$ and the tau slepton $\tilde{τ}_{1}$ in a simplified model of supersymmetry with a nearly massless gravitino. In this model, masses up to m ($\tilde{t}_{1}$) = 1.16 TeV and m ($\tilde{τ}_{1}$) = 1.00 TeV are excluded at 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the W-boson mass in pp collisions at $\sqrt{s}=7 TeV$ with the ATLAS detector

A measurement of the mass of the W boson is presented based on proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb -1 of integrated luminosity. The selected data sample consists of 7.8 × 10 6 candidates in the W→μν channel and 5.9×10 6 candidates in the W→eν channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding m W =80370 ± 7 (stat.) ± 11 (exp.syst.) ±14 (mod.syst.) MeV = 80370 ± 19 MeV where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. Finally, a measurement of the mass difference between the W + and W - bosons yields m W + -m W = -29 ± 28 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for new phenomena in high-mass final states with a photon and a jet from $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7 fb -1 of proton–proton collisions at a centre-of-mass energy of s√ = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed–Dimopoulos–Dvali (Randall–Sundrum) model with six (one) extra dimensions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗