Showing papers by "Lillian Smestad published in 2017"
TL;DR: This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton–proton collision data.
Abstract: During 2015 the ATLAS experiment recorded 3.8 fb(-1) of proton-proton collision data at a centre-of-mass energy of 13 TeV. The ATLAS trigger system is a crucial component of the experiment, respons ...
488 citations
TL;DR: Topological cell clustering is established as a well-performing calorimeter signal definition for jet and missing transverse momentum reconstruction in ATLAS and is exploited to apply a local energy calibration and corrections depending on the nature of the cluster.
Abstract: The reconstruction of the signal from hadrons and jets emerging from the proton–proton collisions at the Large Hadron Collider (LHC) and entering the ATLAS calorimeters is based on a three-dimensional topological clustering of individual calorimeter cell signals. The cluster formation follows cell signal-significance patterns generated by electromagnetic and hadronic showers. In this, the clustering algorithm implicitly performs a topological noise suppression by removing cells with insignificant signals which are not in close proximity to cells with significant signals. The resulting topological cell clusters have shape and location information, which is exploited to apply a local energy calibration and corrections depending on the nature of the cluster. Topological cell clustering is established as a well-performing calorimeter signal definition for jet and missing transverse momentum reconstruction in ATLAS.
438 citations
TL;DR: In this article, a sample of proton-proton collisions at 8$ TeV, corresponding to an integrated luminosity of 11.4 fb$^{-1}$ collected in 2012 with the ATLAS detector at the LHC.
Abstract: The production of two prompt $J/\psi$ mesons, each with transverse momenta $p_{\mathrm{T}}>8.5$ GeV and rapidity $|y| < 2.1$, is studied using a sample of proton-proton collisions at $\sqrt{s} = 8$ TeV, corresponding to an integrated luminosity of 11.4 fb$^{-1}$ collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised $J/\psi$ production, is measured as a function of the transverse momentum of the lower-$p_{\mathrm{T}}$ $J/\psi$ meson, di-$J/\psi$ $p_{\mathrm{T}}$ and mass, the difference in rapidity between the two $J/\psi$ mesons, and the azimuthal angle between the two $J/\psi$ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two $J/\psi$ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be $\sigma_{\mathrm{eff}} = 6.3 \pm 1.6 \mathrm{(stat)} \pm 1.0 \mathrm{(syst)} \pm 0.1 \mathrm{(BF)} \pm 0.1 \mathrm{(lumi)}$ mb.
96 citations
TL;DR: In this paper, a measurement of the t-channel single-top-quark and single top-antiquark production cross-sections in the lepton+jets channel is presented, using 3.2 fb−1 of proton-proton collision data.
Abstract: A measurement of the t-channel single-top-quark and single-top-antiquark production cross-sections in the lepton+jets channel is presented, using 3.2 fb−1 of proton-proton collision data at a centr ...
74 citations
TL;DR: The reconstruction and calibration algorithms used to calculate missing transverse momentum with the ATLAS detector exploit energy deposits in the calorimeter and tracks reconstructed in the inner detector as well as the muon spectrometer to suppress effects arising from additional proton–proton interactions concurrent with the hard-scatter processes.
Abstract: The reconstruction and calibration algorithms used to calculate missing transverse momentum ($E_{\rm T}^{\rm miss}$) with the ATLAS detector exploit energy deposits in the calorimeter and tracks reconstructed in the inner detector as well as the muon spectrometer. Various strategies are used to suppress effects arising from additional proton-proton interactions, called pileup, concurrent with the hard-scatter processes. Tracking information is used to distinguish contributions from the pileup interactions using their vertex separation along the beam axis. The performance of the $E_{\rm T}^{\rm miss}$ reconstruction algorithms, especially with respect to the amount of pileup, is evaluated using data collected in proton-proton collisions at a centre-of-mass energy of 8 TeV during 2012, and results are shown for a data sample corresponding to an integrated luminosity of 20.3 fb$^{-1}$. The results of simulation modelling of $E_{\rm T}^{\rm miss}$ in events containing a $Z$ boson decaying to two charged leptons (electrons or muons) or a $W$ boson decaying to a charged lepton and a neutrino is compared to data. The acceptance for different event topologies, with and without high transverse momentum neutrinos, is shown for a range of threshold criteria for $E_{\rm T}^{\rm miss}$, and estimates of the systematic uncertainties in the $E_{\rm T}^{\rm miss}$ measurements are presented.
68 citations
TL;DR: In this article, the production cross section of a Z boson in association with jets in proton-proton collisions at root s = 13TeV was measured using data corresponding to an integrated luminosity.
Abstract: Measurements of the production cross section of a Z boson in association with jets in proton-proton collisions at root s = 13TeV are presented, using data corresponding to an integrated luminosity
60 citations
TL;DR: In this article, the authors presented a search for new resonances with mass larger than 250 GeV, decaying to a Z boson and a photon, and the data were found to be consistent with the expected background in the whole mass range investigated and upper limits were set on the production cross section times decay branching ratio to Z\gamma.
53 citations
TL;DR: In this article, a measurement of the polarisation of W bosons from t (t) over bar t decays, reconstructed in events with one high p(T) lepton and at least four jets, is presented.
Abstract: This paper presents a measurement of the polarisation of W bosons from t (t) over bar t decays, reconstructed in events with one high-p(T) lepton and at least four jets. Data from pp collisions at ...
46 citations
TL;DR: In this article, the electroweak production of a W boson in association with two jets at high dijet invariant mass was performed using root s = 7 and 8 TeV proton-proton collision data.
Abstract: Measurements of the electroweak production of a W boson in association with two jets at high dijet invariant mass are performed using root s = 7 and 8 TeV proton-proton collision data produced by t ...
41 citations
TL;DR: The top-quark mass was measured in the all-hadronic top-antitop quark decay channel using proton-proton collisions at a centre-of-mass energy of s=8.
Abstract: The top-quark mass is measured in the all-hadronic top-antitop quark decay channel using proton-proton collisions at a centre-of-mass energy of s=8" role="presentation">s√=8 TeV with the ATLAS d ...
37 citations
TL;DR: In this paper, a search for new resonances decaying to a $W$ or $Z$ boson and a Higgs boson in collisions at the Large Hadron Collider using a total integrated luminosity of 3.2 fb$^{-1}
TL;DR: In this article, charged particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a center-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb−1.
Abstract: We present charged-particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb−1. The distributions were constructed using charged particles with absolute pseudorapidity less than 2.5 and with transverse momentum greater than 500 MeV, in events with at least one such charged particle with transverse momentum above 1 GeV. These distributions characterise the angular distribution of energy and particle flows with respect to the charged particle with highest transverse momentum, as a function of both that momentum and of charged-particle multiplicity. The results have been corrected for detector effects and are compared to the predictions of various Monte Carlo event generators, experimentally establishing the level of underlying-event activity at LHC Run 2 energies and providing inputs for the development of event generator modelling. The current models in use for UE modelling typically describe this data to 5% accuracy, compared with data uncertainties of less than 1%.
TL;DR: In this paper, a search for triboson production in two decay channels was carried out in the Large Hadron Collider with an expected upper bound of 730 fb with the expected limit of 560 fb in the absence of SM.
Abstract: This paper reports a search for triboson $W^{\pm}W^{\pm}W^{\mp}$ production in two decay channels ($W^{\pm}W^{\pm}W^{\mp}\rightarrow \ell^{\pm}
u\ell^{\pm}
u\ell^{\mp}
u$ and $W^{\pm}W^{\pm}W^{\mp}\rightarrow \ell^{\pm}
u\ell^{\pm}
u{}jj$ with $\ell=e, \mu$) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ at a centre-of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95 % confidence level upper limit on the SM $W^{\pm}W^{\pm}W^{\mp}$ production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM $W^{\pm}W^{\pm}W^{\mp}$ production. Limits are also set on $WWWW$ anomalous quartic gauge couplings.
TL;DR: In this paper, measurements of top quark spin observables were performed in the dilepton final state, characterised by the presence of two isolated leptons (electrons or muons).
Abstract: Measurements of top quark spin observables in $t\bar{t}$ events are presented based on 20.2 fb$^{-1}$ of $\sqrt{s} = 8$ TeV proton-proton collisions recorded with the ATLAS detector at the LHC. The analysis is performed in the dilepton final state, characterised by the presence of two isolated leptons (electrons or muons). There are 15 observables, each sensitive to a different coefficient of the spin density matrix of $t\bar{t}$ production, which are measured independently. Ten of these observables are measured for the first time. All of them are corrected for detector resolution and acceptance effects back to the parton and stable-particle levels. The measured values of the observables at parton level are compared to Standard Model predictions at next-to-leading order in QCD. The corrected distributions at stable-particle level are presented and the means of the distributions are compared to Monte Carlo predictions. No significant deviation from the Standard Model is observed for any observable.
TL;DR: The dynamics of isolated-photon plus one-, two-and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV were studied with the ATLAS detector at the LHC using a data set with an...
TL;DR: While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets.
Abstract: Measurements of jet activity in top-quark pair events produced in proton-proton collisions are presented, using 3.2 fb of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATL ...
TL;DR: In this article, the authors proposed a method to find the optimal set of features for each node in a set of images, which can be found under doi:10.1140/epjc/s10052-016-3910-6
Abstract: The online version of the original article can be found under doi:10.1140/epjc/s10052-016-3910-6
TL;DR: This is a list of notable people from Italy and abroad who have contributed to the development of computer science in the past 25 years and what they have achieved since then.
Abstract: R. Caravita, S. Aghion, C. Amsler , G. Bonomi, R.S. Brusa M. Caccia, F. Castelli, G. Cerchiari, D. Comparat, G. Consolati A. Demetrio, L. Di Noto, M. Doser, C. Evans, R. Ferragut J. Fesel, A. Fontana, S. Gerber, M. Giammarchi, A. Gligorova F. Guatieri, S. Haider, A. Hinterberger, H. Holmestad A. Kellerbauer, O. Khalidova, D. Krasnický, V. Lagomarsino P. Lansonneur, P. Lebrun, C. Malbrunot , S. Mariazzi, J. Marton V. Matveev, Z. Mazzotta, S.R. Müller, G. Nebbia, P. Nedelec M. Oberthaler, N. Pacifico, D. Pagano, L. Penasa, V. Petracek F. Prelz, M. Prevedelli, L. Ravelli, B. Rienäcker, J. Robert O.M. Røhne, A. Rotondi, H. Sandaker, R. Santoro, L. Smestad F. Sorrentino, G. Testera, I. Tietje, E. Widmann , P. Yzombard C. Zimmer, J. Zmeskal , N. Zurlo
TL;DR: In this article, the authors measured the particle multiplicities resulting from antiproton annihilations on nuclei and compared with predictions obtained using different models in the simulation tools GEANT4 and FLUKA.
Abstract: The characteristics of low energy antiproton annihilations on nuclei (e.g. hadronization and product multiplicities) are not well known, and Monte Carlo simulation packages that use different models provide different descriptions of the annihilation events. In this study, we measured the particle multiplicities resulting from antiproton annihilations on nuclei. The results were compared with predictions obtained using different models in the simulation tools GEANT4 and FLUKA. For this study, we exposed thin targets (Cu, Ag and Au) to a very low energy antiproton beam from CERN's Antiproton Decelerator, exploiting the secondary beamline available in the AEgIS experimental zone. The antiproton annihilation products were detected using emulsion films developed at the Laboratory of High Energy Physics in Bern, where they were analysed at the automatic microscope facility. The fragment multiplicity measured in this study is in good agreement with results obtained with FLUKA simulations for both minimally and heavily ionizing particles.
TL;DR: In this article, a measurement of the tau + jets final state using only the hadronic decays of tau lepton is presented, and the measurement is p = t (t) over bar + X production cross section.
Abstract: A measurement of the inclusive pp -> t (t) over bar + X production cross section in the tau + jets final state using only the hadronic decays of the tau lepton is presented. The measurement is p ...
25 Mar 2017
TL;DR: The AEGIS experiment 1 (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is planned to perform the first measurement of the gravitational acceleration on antimatter by observing the free fall of antihydrogen atoms as discussed by the authors.
Abstract: The AEGIS experiment 1 (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is planned to perform the first measurement of the gravitational acceleration on antimatter by observing the free fall of antihydrogen atoms. By combining techniques based on recent developments in the production of positronium and its laser excitation to Rydberg states, such a study seems indeed to be feasible for neutral antimatter. We present here some of the experimental techniques involved in the experiment as well as the status of the detector test envisioned for the gravity measurement.
24 Nov 2017
TL;DR: The list of winners and runners-up in this year's Tournaisian Cup includes:.
Abstract: P. Yzombard1, C. Amsler2, T. Ariga2, G. Bonomi3,4, P. Bräunig5, R. S. Brusa6,7, L. Cabaret1, M. Caccia8, R. Caravita9,10,14, F. Castelli8,11, G. Cerchiari12, D. Comparat1, G. Consolati8,13, A. Demetrio5, L. Di Noto9,10, M. Doser14, A. Ereditato2, C. Evans8,13, R. Ferragut8,13, J. Fesel14, A. Fontana4, S. Gerber14, M. Giammarchi8, A. Gligorova15, F. Guatieri6,7, S. Haider14, H. Holmestad16, T. Huse16, A. Kellerbauer12, D. Krasnický9,10, V. Lagomarsino9,10, P. Lansonneur17, P. Lebrun17, C. Malbrunot14,18, S. Mariazzi18, V. Matveev19,20, Z. Mazzotta8,11, G. Nebbia21, P. Nedelec17, M. Oberthaler5, N. Pacifico15, D. Pagano3,4, L. Penasa6,7, V. Petracek22, C. Pistillo2, F. Prelz8, M. Prevedelli23, L. Ravelli6,7, B. Rienaecker14, O.M. Røhne16, A. Rotondi4,24, M. Sacerdoti8,11, H. Sandaker16, R. Santoro8,25, P. Scampoli2,26, L. Smestad14,27, F. Sorrentino9,10, I. M. Strojek22, G. Testera10, I. C. Tietje14, S. Vamosi18, E. Widmann18, J. Zmeskal18, N. Zurlo4,28