Browsing by Author "Silva, J."
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- Angular distributions in $t \overline{t}H(H → b \overline{b})$ reconstructed events at the LHCPublication . Amor dos Santos, S. P.; Araque, J.P.; Cantrill, R.; Castro, N.F.; Fiolhais, M.C.N.; Frederix, R.; Gonçalo, R.; Martins, R.; Santos, R.; Silva, J.; Onofre, A.; Peixoto, H.; Reigoto, A.The associated production of a Higgs boson and a top-quark pair, $t{\bar t} H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13TeV at the LHC. Dileptonic final states of $t{\bar t}H$ events with two oppositely charged leptons and four jets from the decays $t\rightarrow bW^+ \rightarrow b \ell^+\nu_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\bar{\nu}_\ell$ and $h\rightarrow b\bar{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay products as well as angular asymmetries are explored in order to improve discrimination of $t{\bar t} H$ signal events over the dominant irreducible background contribution, $t{\bar t}b{\bar b}$. Even after the full kinematic fit reconstruction of the events, the proposed angular distributions and asymmetries are still quite different in the $t\bar{t}H$ signal and the dominant background ($t\bar{t}b\bar{b}$).
- Mechanical construction and installation of the ATLAS tile calorimeterPublication . ATLAS Tile Calorimeter collaboration (234 authors); Alves, R.; Amaral, P.; Carvalho, J.; David, M.; Gomes, A.; Maio, A.; Marques, C.; Onofre, A.; Pereira, A.; Pina, J.; Pinhão, J.; Santos, J.; Saraiva, J.G.; Silva, J.This paper summarises the mechanical construction andinstallation of the Tile Calorimeter for the ATLASexperiment at the Large Hadron Collider in CERN, Switzerland. The TileCalorimeter is a sampling calorimeter using scintillator as the sensitivedetector and steel as the absorber and covers the central region of the ATLASexperiment up to pseudorapidities ±1.7. The mechanical construction ofthe Tile Calorimeter occurred over a periodof about 10 years beginning in 1995 with the completionof the Technical Design Report and ending in 2006 with the installationof the final module in the ATLAS cavern. Duringthis period approximately 2600 metric tons of steel were transformedinto a laminated structure to form the absorber of the sampling calorimeter.Following instrumentation and testing, which is described elsewhere, themodules were installed in the ATLAS cavern with a remarkable accuracy fora structure of this size and weight.
- Musculoskeletal Disorders and Work Capacity in Portuguese NavyPublication . Henriques, Moisés Santos; Alves, A.; Carrilho, J.; Nunes, A.; Albergaria, F.; Diniz, M.; Silva, J.
- Probing the CP nature of the Higgs coupling in $t{\bar t}h$ events at the LHCPublication . Amor Dos Santos, S.; Fiolhais, M.C.N.; Frederix, R.; Gonçalo, R.; Gouveia, E.; Martins, R.; Onofre, A.; Pease, C.M.; Peixoto, H.; Reigoto, A.; Santos, R.; Silva, J.The determination of the CP nature of the Higgs coupling to top quarks is addressed in this paper, using tt¯h events produced in s=13 TeV proton-proton collisions at the LHC. Dileptonic final states are employed, with two oppositely charged leptons and four jets, corresponding to the decays t→bW+→bℓ+νℓ, t¯→b¯W-→b¯ℓ-ν¯ℓ, and h→bb¯. Pure scalar (h=H), pure pseudoscalar (h=A), and CP-violating Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed through a kinematic fit. We furthermore generate samples that have both a CP-even and a CP-odd component in the tt¯h coupling in order to probe the ratio of the two components. New angular distributions of the decay products, as well as CP angular asymmetries, are explored in order to separate the scalar from the pseudoscalar components of the Higgs boson and reduce the contribution from the dominant irreducible background, tt¯bb¯. Significant differences between the angular distributions and asymmetries are observed, even after the full kinematic fit reconstruction of the events, allowing to define the best observables for a global fit of the Higgs couplings parameters.
- The Laser calibration of the Atlas Tile Calorimeter during the LHC run 1Publication . ATLAS Tile Calorimeter system collaboration (238 authors); Santos, S.P.Amor Dos; Araque, J.P.; Castro, A.Blanco; Carvalho, J.; Castro, N.F.; De Sousa, M.J.Da Cunha Sargedas; Fiolhais, M.C.N.; Galhardo, B.; Gomes, A.; Jorge, P.M.; Martins, P.J.Magalhaes; Maio, A.; Maneira, J.; Seabra, L.F.Oleiro; Onofre, A.; Pedro, R.; Pina, J.; Santos, H.; Saraiva, J.G.; Silva, J.; Delgado, A.Tavares; Veloso, F.This article describes the Laser calibration system of the Atlas hadronic Tile Calorimeter that has been used during the run 1 of the LHC. First, the stability of the system associated readout electronics is studied. It is found to be stable with variations smaller than 0.6 %. Then, the method developed to compute the calibration constants, to correct for the variations of the gain of the calorimeter photomultipliers, is described. These constants were determined with a statistical uncertainty of 0.3 % and a systematic uncertainty of 0.2 % for the central part of the calorimeter and 0.5 % for the end-caps. Finally, the detection and correction of timing mis-configuration of the Tile Calorimeter using the Laser system are also presented.