Showing papers by "A. Ferretto Parodi published in 2016"
TL;DR: In this article, the performance of the ATLAS muon identification and reconstruction using the first LHC dataset recorded at s√ = 13 TeV in 2015 was evaluated using the Monte Carlo simulations.
Abstract: This article documents the performance of the ATLAS muon identification and reconstruction using the first LHC dataset recorded at s√ = 13 TeV in 2015. Using a large sample of J/ψ→μμ and Z→μμ decays from 3.2 fb−1 of pp collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to 99% over most of the covered phase space (|η| 2.2, the pT resolution for muons from Z→μμ decays is 2.9% while the precision of the momentum scale for low-pT muons from J/ψ→μμ decays is about 0.2%.
440 citations
TL;DR: In this paper, an independent b-tagging algorithm based on the reconstruction of muons inside jets as well as the b tagging algorithm used in the online trigger are also presented.
Abstract: The identification of jets containing b hadrons is important for the physics programme of the ATLAS experiment at the Large Hadron Collider. Several algorithms to identify jets containing b hadrons are described, ranging from those based on the reconstruction of an inclusive secondary vertex or the presence of tracks with large impact parameters to combined tagging algorithms making use of multi-variate discriminants. An independent b-tagging algorithm based on the reconstruction of muons inside jets as well as the b-tagging algorithm used in the online trigger are also presented. The b-jet tagging efficiency, the c-jet tagging efficiency and the mistag rate for light flavour jets in data have been measured with a number of complementary methods. The calibration results are presented as scale factors defined as the ratio of the efficiency (or mistag rate) in data to that in simulation. In the case of b jets, where more than one calibration method exists, the results from the various analyses have been combined taking into account the statistical correlation as well as the correlation of the sources of systematic uncertainty.
362 citations
TL;DR: The methods employed in the ATLAS experiment to correct for the impact of pile-up on jet energy and jet shapes, and for the presence of spurious additional jets, are described, with a primary focus on the large 20.3 kg-1 data sample.
Abstract: The large rate of multiple simultaneous protonproton interactions, or pile-up, generated by the Large Hadron Collider in Run 1 required the development of many new techniques to mitigate the advers ...
316 citations
TL;DR: The results suggest that the ridge in pp collisions arises from the same or similar underlying physics as observed in p+Pb collisions, and that the dynamics responsible for the ridge has no strong sqrt[s] dependence.
Abstract: ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, $\Delta \phi$, and pseudorapidity, $\Delta \eta$, in $\sqrt{s}$=13 and 2.76 TeV $pp$ collisions at the LHC using charged particles measured in the pseudorapidity interval $|\eta|$<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at $\Delta \phi \sim 0$ that extends over a wide range of $\Delta\eta$, which has been referred to as the "ridge". Per-trigger-particle yields, $Y(\Delta \phi)$, are measured over 2<$|\Delta\eta|$<5. For both collision energies, the $Y(\Delta \phi)$ distribution in all multiplicity intervals is found to be consistent with a linear combination of the per-trigger-particle yields measured in collisions with less than 20 reconstructed tracks, and a constant combinatoric contribution modulated by $\cos{(2\Delta \phi)}$. The fitted Fourier coefficient, $v_{2,2}$, exhibits factorization, suggesting that the ridge results from per-event $\cos{(2\phi)}$ modulation of the single-particle distribution with Fourier coefficients $v_2$. The $v_2$ values are presented as a function of multiplicity and transverse momentum. They are found to be approximately constant as a function of multiplicity and to have a $p_{\mathrm{T}}$ dependence similar to that measured in $p$+Pb and Pb+Pb collisions. The $v_2$ values in the 13 and 2.76 TeV data are consistent within uncertainties. These results suggest that the ridge in $pp$ collisions arises from the same or similar underlying physics as observed in $p$+Pb collisions, and that the dynamics responsible for the ridge has no strong $\sqrt{s}$ dependence.
246 citations
TL;DR: In this paper, a measurement of the inelastic proton-proton cross section using 60''μb^{-1} of pp collisions at a center-of-mass energy sqrt[s] of 13'TeV with the ATLAS detector at the LHC is presented.
Abstract: This Letter presents a measurement of the inelastic proton-proton cross section using 60 μb^{-1} of pp collisions at a center-of-mass energy sqrt[s] of 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region (2.07 10^{-6}, where M_{X} is the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this ξ range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with M_{X}>13 GeV. The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of 78.1±2.9 mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy.
191 citations
TL;DR: In this article, the authors describe a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model.
185 citations
TL;DR: In this article, the authors measured the transverse momentum and the related angular variable of DrellΓCoYan lepton pairs with the ATLAS detector at the LHC and compared their results to predictions from perturbative and resummed QCD calculations.
Abstract: Distributions of transverse momentum [Formula: see text] and the related angular variable [Formula: see text] of DrellΓCoYan lepton pairs are measured in 20.3┬afb[Formula: see text] of protonΓCoproton collisions at [Formula: see text]┬aTeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in protonΓCoproton collisions at [Formula: see text]┬aTeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of [Formula: see text] the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of [Formula: see text] this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of [Formula: see text] while the fixed-order prediction of Dynnlo falls below the data at high values of [Formula: see text]. ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the [Formula: see text] and [Formula: see text] distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.
160 citations
TL;DR: In this article, a search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons (e or μ) with the same electric charge or at the same location.
Abstract: A search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons (e or μ) with the same electric charge or at ...
159 citations
TL;DR: Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described in this article, based on protonproton collision data corresponding to two photons.
Abstract: Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on protonproton collision data corresponding to ...
155 citations
TL;DR: In this paper, measurements of the W-+/- = e(+/-) v and Z = l(+)l(-) production cross sections in proton-proton collisions at root s = 13 TeV are presented.
126 citations
TL;DR: In this paper, a search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC.
Abstract: A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of H → invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgs-portal dark matter where the branching fraction limit is converted into upper bounds on the dark-matter-nucleon scattering cross section as a function of the dark-matter particle mass, and compared to results from the direct dark-matter detection experiments.
TL;DR: In this paper, measurements of W(+/-)Z production in pp collisions at a center-of-mass energy of 8 TeV were presented, where the gauge bosons were reconstructed using their leptonic decay modes into electrons and m...
Abstract: This paper presents measurements of W(+/-)Z production in pp collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and m ...
TL;DR: In this paper, the authors present a survey of NSF projects in the European Union and the United States of America, including the following countries: Austria, Australia, Germany, Austria, Belgium, Canada, Czech Republic, Denmark, Netherlands, Norway, Portugal, Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom, United States, Netherlands and Switzerland.
Abstract: ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq, Brazil; FAPESP, Brazil; NSERC, Canada; NRC, Canada; CFI, Canada; CERN; CONICYT, Chile; CAS, China; MOST, China; NSFC, China; COLCIEN-CIAS, Colombia; MSMT CR, Czech Republic; MPO CR, Czech Republic; VSC CR, Czech Republic; DNRF, Denmark; DNSRC, Denmark; Lundbeck Foundation, Denmark; EPLANET; ERC; NSRF; European Union; IN2P3-CNRS, France; CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, Germany; DFG, Germany; HGF, Germany; MPG, Germany; AvH Foundation, Germany; GSRT, Greece; NSRF, Greece; ISF, Israel; MINERVA, Israel; GIF, Israel; DIP, Israel; Benoziyo Center, Israel; INFN, Italy; MEXT, Japan; JSPS, Japan; CNRST, Morocco; FOM, Netherlands; NWO, Netherlands; BRF, Norway; RCN, Norway; MNiSW, Poland; GRICES, Portugal; FCT, Portugal; MERYS (MECTS), Romania; MES of Russia; ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS, Slovenia; MIZS, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC, Sweden; Wallenberg Foundation, Sweden; SER, Switzerland; SNSF, Switzerland; Canton of Bern, Switzerland; Canton of Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, United Kingdom; Royal Society, United Kingdom; Leverhulme Trust, United Kingdom; DOE, United States of America; NSF, United States of America
TL;DR: Results of a search for new phenomena in events with at least three photons are reported, with limits at the 95 % confidence level on new phenomena presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay of the Higgs boson.
Abstract: Results of a search for new phenomena in events with at least three photons are reported. Data from proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated lumi ...
TL;DR: In this paper, a search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented; the data were recorded in 2015 by the ATLAS experiment.
Abstract: A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment ...
TL;DR: In this paper, the authors presented evidence for single top-quark production in the s-channel using proton-proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Co...
TL;DR: Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described in an effective field theory framework, in which the strength of CP violation is governed by a single parameter.
Abstract: A test of CP invariance in Higgs boson production via vector-boson fusion using the method of the Optimal Observable is presented. The analysis exploits the decay mode of the Higgs boson into a pai ...
TL;DR: The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described and the results are compared to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data.
Abstract: The algorithms used by the ATLAS Collaboration to reconstruct and identify prompt photons are described. Measurements of the photon identification efficiencies are reported, using 4.9 fb$^{-1}$ of $pp$ collision data collected at the LHC at $\sqrt{s} = 7$ TeV and 20.3 fb$^{-1}$ at $\sqrt{s} = 8$ TeV. The efficiencies are measured separately for converted and unconverted photons, in four different pseudo rapidity regions, for transverse momenta between 10 GeV and 1.5 TeV. The results from the combination of three data-driven techniques are compared to the predictions from a simulation of the detector response, after correcting the electromagnetic shower momenta in the simulation for the average differences observed with respect to data. Data-to-simulation efficiency ratios used as correction factors in physics measurements are determined to account for the small residual efficiency differences. These factors are measured with uncertainties between 0.5% and 10% in 7 TeV data and between 0.5% and 3% in 8 TeV data, depending on the photon transverse momentum and pseudorapidity.
TL;DR: The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction.
Abstract: This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction. The performance of the reconstruction algorithm is optimised and evaluated using simulation and validated using samples of [Formula: see text] and [Formula: see text]+jets events selected from proton-proton collisions at a centre-of-mass energy [Formula: see text], corresponding to an integrated luminosity of 5 [Formula: see text].
TL;DR: In this paper, a detailed study of techniques for identifying boosted, hadronically decaying W bosons using 20.3 fb −¹ of proton-proton collision data collected by the ATLAS detector at the LHC at a center-of-mass energy √s = 8 TeV.
Abstract: This paper reports a detailed study of techniques for identifying boosted, hadronically decaying W bosons using 20.3 fb −¹ of proton–proton collision data collected by the ATLAS detector at the LHC at a centre-of-mass energy √s = 8 TeV. A range of techniques for optimising the signal jet mass resolution are combined with various jet substructure variables. The results of these studies in Monte Carlo simulations show that a simple pairwise combination of groomed jet mass and one substructure variable can provide a 50 % efficiency for identifying W bosons with transverse momenta larger than 200 GeV while maintaining multijet background efficiencies of 2–4 % for jets with the same transverse momentum. These signal and background efficiencies are confirmed in data for a selection of tagging techniques.
01 Mar 2016
TL;DR: In this article, the authors summarized and extended the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches, including vector-boson fusion, initial-state radiation jets, and low-momentum lepton final states.
Abstract: The ATLAS experiment has performed extensive searches for the electroweak production of charginos, neutralinos and staus. This article summarizes and extends the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches. New searches use vector-boson fusion production, initial-state radiation jets, and low-momentum lepton final states, as well as multivariate analysis techniques to improve the sensitivity to scenarios with small mass splittings and low-production cross-sections. Results are based on 20 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$=8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. The new and existing searches are combined and interpreted in terms of 95% confidence-level exclusion limits in simplified models, where a single production process and decay mode is assumed, as well as within phenomenological supersymmetric models.
TL;DR: A measurement of the average number of charged particles inside jets using 20.3 fb of data recorded with the ATLAS detector in dijet events using quark and gluon jet fractions and the resulting charged-particle multiplicity is compared to several models.
Abstract: The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-pertur ...
TL;DR: In this article, a search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb(-1) of proton-proton collision data at root s = 8 TeV.
Abstract: A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb(-1) of proton-proton collision data at root s = 8 TeV. The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched for in events with either two hadronically decaying tau leptons, one hadronically decaying tau and one light lepton, or two light leptons. No significant excess over the Standard Model expectation is found. Exclusion limits at 95 % confidence level are set as a function of the top squark and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV LEP limit to the top squark mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered.
TL;DR: In this paper, the authors measured the charged particle distributions in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity.
TL;DR: The production rates of prompt and non-prompt mesons in their dimuon decay modes are measured using data collected with the ATLAS experiment at the Large Hadron Collider, in proton–proton collisions at s=7 and 8 respectively.
Abstract: The production rates of prompt and non-prompt J/psi and psi(2S) mesons in their dimuon decay modes are measured using 2.1 and 11.4 fb(-1) of data collected with the ATLAS experiment at the Large Ha ...
TL;DR: In this paper, the production of W-+/- Z events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC.
TL;DR: In this paper, the ATLAS experiment at the Large Hadron Collider was used to measure photon production in root S-NN = 2.76-TeV Pb + Pb collisions.
Abstract: Prompt photon production in root S-NN = 2.76-TeV Pb + Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity ...
TL;DR: The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV as mentioned in this paper.
Abstract: The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV. The measur ...
TL;DR: In this paper, the per-event charged particle yield as a function of the charged-particle transverse momentum and rapidity is performed using p+Pbp+Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of sqrt (SNN) = 5.01 TeV.
TL;DR: In this article, the cross-section for the production of a single top quark in association with a W boson in proton-proton collisions at is measured and the dataset corresponds to an integrated luminosity of 20.3 fb(-...
Abstract: The cross-section for the production of a single top quark in association with a W boson in proton-proton collisions at is measured. The dataset corresponds to an integrated luminosity of 20.3 fb(- ...