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Angelozzi, I.

Publications and source records attributed to Angelozzi, I..

At least 91 records · Page 5
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DOE OSTI2018

Search for Higgs boson pair production in the γγWW* channel using $pp$ collision data recorded at $\sqrt{s}$ $=13$ TeV with the ATLAS detector

Searches for non-resonant and resonant Higgs boson pair production are performed in the γγWW* channel with the final state of γγℓνjj using 36.1 fb -1 of proton–proton collision data recorded at a centre-of-mass energy of √s= 13 TeV by the ATLAS detector at the Large Hadron Collider. No significant deviation from the Standard Model prediction is observed. A 95% confidence-level observed upper limit of 7.7 pb is set on the cross section for non-resonant production, while the expected limit is 5.4 pb. A search for a narrow-width resonance X decaying to a pair of Standard Model Higgs bosons HH is performed with the same set of data, and the observed upper limits on σ(pp→X) × B(X→HH) range between 40.0 and 6.1 pb for masses of the resonance between 260 and 500 GeV, while the expected limits range between 17.6 and 4.4 pb. When deriving the limits above, the Standard Model branching ratios of the H→γγ and H→WW* are assumed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the azimuthal anisotropy of charged particles produced in $\sqrt{s_{_\text {NN}}}$ = 5.02 TeV Pb+Pb collisions with the ATLAS detector

Measurements of the azimuthal anisotropy in lead–lead collisions at $\sqrt{s_{_\text {NN}}}$ = 5.02 TeV are presented using a data sample corresponding to 0.49 nb -1 integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for “ultra-central” collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, v 2 - v 7 , which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics v n over wide ranges of the transverse momentum, 0.5 < p T < 60 GeV, the pseudorapidity, |η|< 2.5, and the collision centrality 0–80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at $\sqrt{s_{_\text {NN}}}$ = 2.76 TeV and 5.02 TeV . In particular, the shape of the p T dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the v n and p T values by constant factors over the centrality interval 0–60% and the p T range 0.5 < p T < 5 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for new phenomena in events with same-charge leptons and b-jets in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector

A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb -1 of pp collisions at √s=13 TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, four-top-quark, and same-sign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like T- and B-quark singlet are m T > 0.98 (0.99) TeV and m B > 1.00 (1.01) TeV respectively. Limits on the production of the vector-like T 5/3 -quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the T 5/3 -quark is (expected to be) 1.19 (1.21) TeV. The Standard Model four-top-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on same-sign top-quark pair production. The upper limit on uu → tt production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for electroweak production of supersymmetric particles in final states with two or three leptons at $\sqrt{s}=13 \hbox {TeV}$ with the ATLAS detector

A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb -1 of √s=13 TeV proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at E beam =4 TeV

Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the \textsc{Fluka} Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared quantitatively with data. Through these comparisons the origins of the BIB leading to different observables in the ATLAS detectors are analysed. The level of agreement between simulation results and BIB measurements by ATLAS in 2012 demonstrates that a good understanding of the origin of BIB has been reached.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Measurement of the Zγ → $\mathcal{v}$$\bar{v}$γ production cross section in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector and limits on anomalous triple gauge-boson couplings

The production of Z bosons in association with a high-energy photon ( Z γ production) is studied in the neutrino decay channel of the Z boson using pp collisions at $\sqrt{s}=13$ TeV. The analysis uses a data sample with an integrated luminosity of 36.1 fb -1 collected by the ATLAS detector at the LHC in 2015 and 2016. Candidate Z γ events with invisible decays of the Z boson are selected by requiring significant transverse momentum (ρ τ ) of the dineutrino system in conjunction with a single isolated photon with large transverse energy (Ε τ ). The rate of Z γ production is measured as a function of photon Ε τ , dineutrino system pT and jet multiplicity. Here, evidence of anomalous triple gauge-boson couplings is sought in Z γ production with photon Ε τ greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZ γ and Z γγ couplings.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Operation and performance of the ATLAS Tile Calorimeter in Run 1

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8 TeV with a total integrated luminosity of nearly 30 fb –1 . The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Lastly, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for charged Higgs bosons decaying into top and bottom quarks at $ \sqrt{s}=13$ TeV with the ATLAS detector

A search for charged Higgs bosons heavier than the top quark and decaying via H ± → tb is presented. The data analysed corresponds to 36.1 fb -1 of pp collisions at √s=13 TeV and was recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark, pp → tbH ± , is explored in the mass range from m H ± = 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass, which range from 2.9 pb at m H ± = 200 GeV to 0.070 pb at m H ± = 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for Higgs boson pair production in the γγ$b\overline{b} $ final state with 13 TeV pp collision data collected by the ATLAS experiment

A search is performed for resonant and non-resonant Higgs boson pair production in the γγ$b\overline{b} $ final state. The data set used corresponds to an integrated luminosity of 36.1 fb -1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess relative to the Standard Model expectation is observed. The observed limit on the non-resonant Higgs boson pair cross-section is 0.73 pb at 95% confidence level. This observed limit is equivalent to 22 times the predicted Standard Model cross-section. The Higgs boson self-coupling (κ λ = λ HHH /λ HHH SM ) is constrained at 95% confidence level to -8.2 < κ λ < 13.2. For resonant Higgs boson pair production through X→HH→γγ$b\overline{b} $, the limit is presented, using the narrow-width approximation, as a function of mX in the range 260 GeV < m X < 1000 GeV. The observed limits range from 1.1 pb to 0.12 pb over this mass range. Open image in new window

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗