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Antonelli, M. (ORCID:0000000222935726)

Publications and source records attributed to Antonelli, M. (ORCID:0000000222935726).

At least 91 records · Page 5
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DOE OSTI2023

Luminosity determination in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC

The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy $\sqrt{s}$ = 13 TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data taking range from 0.9% to 1.1%, and are partially corre lated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 ± 1.2 fb -1 , i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017– 2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 ± 3.1 pb -1 .

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DOE OSTI2023

Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector

This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb -1 of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688±23(stat) $^{+75}_{-71}$(syst) fb, to be compared with the standard model prediction of 515$^{+36}_{-42}$ fb at next-to-leading order in QCD.

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DOE OSTI2023

Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in Pb+Pb Collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with the ATLAS Detector

This letter presents a measurement of the nuclear modification factor of large-radius jets in $\sqrt{s_{NN}}$ = 5.02 TeV Pb + Pb collisions by the ATLAS experiment. The measurement is performed using 1.72 nb –1 and 257 pb –1 of Pb + Pb and pp data, respectively. The large-radius jets are reconstructed with the anti-k t algorithm using a radius parameter of R = 1.0, by reclustering anti-k t R = 0.2 jets, and are measured over the transverse momentum (p T ) kinematic range of 158 < p T <1000 GeV and absolute pseudorapidity |y| < 2.0. The large-radius jet constituents are further reclustered using the k t algorithm in order to obtain the splitting parameters, $\sqrt{d_{12}}$ and Δ⁢R 12 , which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, R AA , obtained by comparing the Pb + Pb jet yields to those in pp collisions, is measured as a function of jet transverse momentum (p T ) and $\sqrt{d_{12}}$ or Δ⁢R 12 . A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of R AA for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression.

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DOE OSTI2023

Measurement of the Sensitivity of Two-Particle Correlations in $\mathcal{pp}$ Collisions to the Presence of Hard Scatterings

A key open question in the study of multiparticle production in high-energy pp collisions is the relationship between the “ridge”—i.e., the observed azimuthal correlations between particles in the underlying event that extend over all rapidities—and hard or semihard scattering processes. In particular, it is not known whether jets or their soft fragments are correlated with particles in the underlying event. To address this question, two-particle correlations are measured in pp collisions at $\sqrt{s}$=13 TeV using data collected by the ATLAS experiment at the LHC, with an integrated luminosity of 15.8 pb -1 , in two different configurations. In the first case, charged particles associated with jets are excluded from the correlation analysis, while in the second case, correlations are measured between particles within jets and charged particles from the underlying event. Second-order flow coefficients, v2, are presented as a function of event multiplicity and transverse momentum. These measurements show that excluding particles associated with jets does not affect the measured correlations. Moreover, particles associated with jets do not exhibit any significant azimuthal correlations with the underlying event, ruling out hard processes contributing to the ridge.

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DOE OSTI2023

Observation of an Excess of Dicharmonium Events in the Four-Muon Final State with the ATLAS Detector

A search is made for potential $cc\bar{c}\bar{c}$ tetraquarks decaying into a pair of charmonium states in the four muon final state using proton-proton collision data at $\sqrt{s}$=13 TeV, corresponding to an integrated luminosity of 140 fb -1 recorded by the ATLAS experiment at LHC. Two decay channels, $J/ψ+J/ψ→4μ$ and $J/ψ+ψ(2S)→4μ$, are studied. Backgrounds are estimated based on a hybrid approach involving Monte Carlo simulations and data-driven methods. Statistically significant excesses with respect to backgrounds dominated by the single parton scattering are seen in the di-J/ψ channel consistent with a narrow resonance at 6.9 GeV and a broader structure at lower mass. A statistically significant excess is also seen in the $J/ψ+ψ$(2S) channel. The fitted masses and decay widths of the structures are reported.

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DOE OSTI2023

Observation of the $γγ → ττ$ Process in $\mathrm{Pb + Pb}$ Collisions and Constraints on the $\tau$-Lepton Anomalous Magnetic Moment with the ATLAS Detector

This Letter reports the observation of τ-lepton pair production in ultraperipheral lead-lead collisions, Pb+Pb→Pb(γγ→ττ)Pb, and constraints on the τ-lepton anomalous magnetic moment, a τ . The dataset corresponds to an integrated luminosity of 1.44 nb -1 of LHC Pb+Pb collisions at $\sqrt{s_{NN}}$ =5.02 TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a τ-lepton decay, an electron or charged-particle track(s) from the other τ-lepton decay, little additional central-detector activity, and no forward neutrons. The γγ→ττ process is observed in Pb+Pb collisions with a significance exceeding 5 standard deviations, and a signal strength of μ ττ =1.03$^{+0.06}_{-0.05}$ assuming the Standard Model value for a τ . To measure a τ , a template fit to the muon transverse-momentum distribution from τ-lepton candidates is performed, using a dimuon (γγ→μμ) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for aτ is -0.057 < a τ < 0.024.

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DOE OSTI2023

Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the $H → WW^* → evμv$ decay channel at 13 TeV with the ATLAS detector

The vector-boson production cross-section for the Higgs boson decay in the H→WW*→eνμν channel is measured as a function of kinematic observables sensitive to the Higgs boson production and decay properties as well as integrated in a fiducial phase space. The analysis is performed using the proton-proton collision data collected by the ATLAS detector in Run 2 of the LHC at $\sqrt{s}$=13 TeV center-of-mass energy corresponding to an integrated luminosity of 139 fb -1 . The different flavor final state is studied by selecting an electron and a muon originating from a pair of W bosons and compatible with the Higgs boson decay. The data are corrected for the effects of detector inefficiency and resolution, and the measurements are compared with different state-of-the-art theoretical predictions. The differential cross-sections are used to constrain anomalous interactions described by dimension-six operators in an Effective Field Theory.

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DOE OSTI2023

Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector

This Letter reports on a search for off-shell production of the Higgs boson using 139 fb —1 of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of $\overline{Z}$ bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are $\overline{Z}$ $\overline{Z}$ → 4$\ell$ and $\overline{Z}$ $\overline{Z}$ → 2$\ell$2$ν$ with $\ell$ = $e$ or $μ$. In the $\overline{Z}$ $\overline{Z}$ → 4$\ell$ final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The backgroundonly hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is ${4.5}_{—2.5}^{+3.3}$ MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level.

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DOE OSTI2023

Measurement of the cross-sections of the electroweak and total production of a Zγ pair in association with two jets in pp collisions at s = 13 TeV with the ATLAS detector

This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Zγ pair in association with two jets. The analysis uses 140 fb –1 of LHC proton–proton collision data taken at $\sqrt{s}$ = 13 TeV recorded by the ATLAS detector during the years 2015–2018. Events with a Z boson candidate decaying into either an e + e – or μ + μ – pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and by using the information about the centrality of the system and is measured with an observed and expected significance well above five standard deviations. The fiducial pp→Zγjj cross-section for the electroweak production is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be $16.8_{–1.8}^{+2.0}$ fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions.

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DOE OSTI2023

Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle $X$ in hadronic final states using $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector

A search is presented for a heavy resonance $Y$ decaying into a Standard Model Higgs boson $H$ and a new particle $X$ in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at $\sqrt{s}$ = 13 TeV collected by the ATLAS detector from 2015 to 2018 is used and corresponds to an integrated luminosity of 139 fb –1 . The search targets the high $Y$-mass region, where the $H$ and $X$ have a significant Lorentz boost in the laboratory frame. A novel application of anomaly detection is used to define a general signal region, where events are selected solely because of their incompatibility with a learned background-only model. It is constructed using a jet-level tagger for signal-model-independent selection of the boosted $X$ particle, representing the first application of fully unsupervised machine learning to an ATLAS analysis. Two additional signal regions are implemented to target a benchmark $X$ decay into two quarks, covering topologies where the $X$ is reconstructed as either a single large-radius jet or two smallradius jets. The analysis selects Higgs boson decays into $b$$\overline{b}$, and a dedicated neural-network-based tagger provides sensitivity to the boosted heavy-flavor topology. No significant excess of data over the expected background is observed, and the results are presented as upper limits on the production cross section $σ$ ($pp$ → $Y$ → $XH$ → $q$$\overline{q}$$b$$\overline{b}$) for signals with $m_Y$ between 1.5 and 6 TeV and $m_X$ between 65 and 3000 GeV

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DOE OSTI2023

Search for Majorana neutrinos in same-sign WW scattering events from pp collisions at $\sqrt{s}=13$ TeV

A search for Majorana neutrinos in same-sign WW scattering events is presented. The analysis uses $\sqrt{s}=13$ TeV proton–proton collision data with an integrated luminosity of 140 fb -1 recorded during 2015–2018 by the ATLAS detector at the Large Hadron Collider. The analysis targets final states including exactly two same-sign muons and at least two hadronic jets well separated in rapidity. The modelling of the main backgrounds, from Standard Model same-sign WW scattering and WZ production, is constrained with data in dedicated signal-depleted control regions. The distribution of the transverse momentum of the second-hardest muon is used to search for signals originating from a heavy Majorana neutrino with a mass between 50 GeV and 20 TeV. No significant excess is observed over the background expectation. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. In addition, the sensitivity to the Weinberg operator is investigated. Upper limits at the 95% confidence level are placed on the squared muon-neutrino–heavy-neutrino mass-mixing matrix element |V μN | 2 as a function of the heavy Majorana neutrino’s mass m N , and on the effective μμ Majorana neutrino mass |m μμ |.

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DOE OSTI2023

Search for pairs of muons with small displacements in pp collisions at s = 13 TeV with the ATLAS detector

A search for new phenomena giving rise to pairs of opposite electrically charged muons with impact parameters in the millimetre range is presented, using 139 fb -1 of $\sqrt{s}$ = 13 TeV pp collision data from the ATLAS detector at the LHC. The search targets the gap in coverage between existing searches targeting final states with leptons with large displacement and prompt leptons. No significant excess over the background expectation is observed and exclusion limits are set on the mass of long-lived scalar supersymmetric muon-partners (smuons) with much lower lifetimes than previously targeted by displaced muon searches. Smuon lifetimes down to 1 ps are excluded for a smuon mass of 100 GeV, and smuon masses up to 520 GeV are excluded for a proper lifetime of 10 ps, at 95% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields.

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DOE OSTI2023

Searches for exclusive Higgs and Z boson decays into a vector quarkonium state and a photon using 139 fb$^{-1}$ of ATLAS $\sqrt{s}=13$ TeV proton–proton collision data

Searches for the exclusive decays of Higgs and Z bosons into a vector quarkonium state and a photon are performed in the μ + μ - γ final state with a proton– proton collision data sample corresponding to an integrated luminosity of 139 fb -1 collected at $\sqrt{s}=13$ TeV with the ATLAS detector at the CERN Large Hadron Collider. The observed data are compatible with the expected back grounds. The 95% confidence-level upper limits on the branching fractions of the Higgs boson decays into J/ψ γ , ψ(2S) γ , and $Υ$(1S, 2S, 3S) γ are found to be 2.0 × 10 -4 , 10.5×10 -4 , and (2.5, 4.2, 3.4)×10 -4 , respectively, assuming Standard Model production of the Higgs boson. The corresponding 95% CL upper limits on the branching fractions of the Z boson decays are 1.2 × 10 -6 , 2.4 × 10 -6 , and (1.1, 1.3, 2.4) × 10 -6 . An observed 95% CL interval of (-133, 175) is obtained for the κ c /κ γ ratio of Higgs boson coupling modifiers, and a 95% CL interval of (-37, 40) is obtained for κ b /κ γ .

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DOE OSTI2023

Measurements of differential cross sections of Higgs boson production through gluon fusion in the $H\rightarrow WW^{*}\rightarrow e\nu \mu \nu$ final state at $\sqrt{s} = 13$ TeV with the ATLAS detector

Higgs boson production via gluon–gluon fusion is measured in the $H\rightarrow WW^{*}\rightarrow e\nu \mu \nu$ decay channel. The dataset utilized corresponds to an integrated luminosity of 139 fb -1 collected by the ATLAS detector from $\sqrt{s} = 13$ TeV proton–proton collisions delivered by the Large Hadron Collider between 2015 and 2018. Differential cross sections are measured in a fiducial phase space restricted to the production of at most one additional jet. The results are consistent with Standard Model expectations, derived using different Monte Carlo generators.

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DOE OSTI2023

Search for flavor-changing neutral-current couplings between the top quark and the Z boson with proton-proton collisions at s = 13 TeV with the ATLAS detector

A search for flavor-changing neutral-current couplings between a top quark, an up or charm quark, and a $Z$ boson is presented, using proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The analyzed data set corresponds to an integrated luminosity of 139 fb -1 . The search targets both single-top-quark events produced as $gq$ → $tZ$ (with $q$ = $u, c$) and top-quark-pair events, with one top quark decaying through the $t$ → $Zq$ channel. The analysis considers events with three leptons (electrons or muons), a $b$-tagged jet, possible additional jets, and missing transverse momentum. The data are found to be consistent with the background-only hypothesis and 95% confidence-level limits on the $t$ → $Zq$ branching ratios, assuming only tensor operators of the Standard Model effective field theory framework contribute to the $tZq$ vertices. These are 6.2 x 10 -5 (13 x 10 -5 ) for $t$ → $Zu$ ($t$ → $Zc$) for a left-handed $tZq$ coupling, and 6.6 x 10 -5 (12 x 10 -5 ) in the case of a right-handed coupling. These results are interpreted as 95% CL upper limits on the strength of the corresponding couplings, yielding limits for |${C}^{(13)*}_{uW}$| and |${C}^{(13)*}_{uB}$| (|${C}^{(31)}_{uW}$| and |${C}^{(31)}_{uB}$|) of 0.15 (0.16), and limits for |${C}^{(23)*}_{uW}$| and |${C}^{(23)*}_{uB}$| (|${C}^{(32)}_{uW}$| and |${C}^{(32)}_{uB}$|) of 0.22 (0.21), assuming a new-physics energy scale Λ NP of 1 TeV.

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DOE OSTI2023

Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS

Parton energy loss in the quark–gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb –1 of Pb+Pb data and 260 pb –1 of pp data, both at $\sqrt{^S{\text{NN}}}$ = 5.02 TeV, with the ATLAS detector. The process $pp$ → γ +jet+X and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum ($p_{\text{T}}$) above 50 GeV and reported as a function of jet $p_{\text{T}}$. This selection results in a sample of jets with a steeply falling $p_{\text{T}}$ distribution that are mostly initiated by the showering of quarks. The $pp$ and Pb+Pb measurements are used to report the nuclear modification factor, $R_{\text{AA}}$, and the fractional energy loss, $S_{\text{loss}}$, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The $R_{\text{AA}}$ and $S_{\text{loss}}$ values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. Finally, the results are also compared with a variety of theoretical models of colour-charge-dependent energy loss.

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DOE OSTI2023

New techniques for jet calibration with the ATLAS detector

A determination of the jet energy scale is presented using proton–proton collision data with a centre-of-mass energy of $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 140 fb -1 collected using the ATLAS detector at the LHC. Jets are reconstructed using the ATLAS particle-flow method that combines charged-particle tracks and topo-clusters formed from energy deposits in the calorimeter cells. The anti-k t jet algorithm with radius parameter R = 0.4 is used to define the jet. Novel jet energy scale calibration strategies developed for the LHC Run 2 are reported that lay the foundation for the jet calibration in Run 3. Jets are calibrated with a series of simulation-based corrections, including state-of-the-art techniques in jet calibration such as machine learning methods and novel in situ calibrations to achieve better performance than the baseline calibration derived using up to 81 fb -1 of Run 2 data. The performance of these new techniques is then examined in the in situ measurements by exploiting the transverse momentum balance between a jet and a reference object. The b -quark jet energy scale using particle flow jets is measured for the first time with around 1% precision using $\gamma$+jet events.

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