Browsing by Author "Onofre, A."
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- Angular distributions in t(t)over-barH(H -> b(b)over-bar) reconstructed events at the LHCPublication . Santos, S. P. Amor dos; 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 (t) over barH, in proton-proton collisions is addressed in this paper for a center of mass energy of 13 TeV at the LHC. Dileptonic final states of t (t) over barH events with two oppositely charged leptons and four jets from the decays t -> bW(+) -> bl(+)v(l), (t) over bar -> (b) over barW(-) -> (b) over barl(-)(v) over bar (l) and h -> b (b) over bar 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 (t) over barH signal events over the dominant irreducible background contribution, t (t) over barb (b) over bar. Even after the full kinematic fit reconstruction of the events, the proposed angular distributions and asymmetries are still quite different in the t (t) over barH signal and the dominant background (t (t) over barb (b) over bar).
- Probing the CP nature of the Higgs coupling in tth events at the LHCPublication . dos Santos, S. Amor; Fiolhais, M. C. N.; Frederix, R.; Goncalo, R.; Gouveia, E.; Martins, R.; Onofre, A.; Pease, C. M.; Peixoto, H.; Reigoto, A.; dos Santos, Rui Alberto; 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 pffisffiffi 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_.l, _ t. _ bW-. _ bl- _.l, and h. b _ b. 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 t _ th 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, t _ tb _ b. 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.
- Search for an invisible scalar in tt¯ final states at the LHCPublication . Azevedo, Duarte; Capucha, Rodrigo; Chaves, Pedro; Martins, João Bravo; Onofre, A.; Santos, RuiWe use the current tt¯ experimental analysis to look for Dark Matter (DM) particles hidden in the final state. We present a phenomenological study where we successfully perform the reconstruction of a tt¯ system in the presence of a scalar mediator Y 0, that couples to both Standard Model (SM) and to DM particles. We use a MadGraph5_aMC@NLO simplified DM model, where signal samples of pp → tt¯ Y 0 are generated at the Large Hadron Collider (LHC) with both Charge-Parity (CP) -even and CP-odd couplings of Y 0 to the top quarks. Different mass scales for the Y 0 mediator are considered, from the low mass region (~ 0 GeV) to masses close to the Higgs boson mass (125 GeV). The dileptonic final states of the tt¯ system were used in our analysis. The reconstruction of the tt¯ system is done with a kinematic fit, without reconstructing the mediator. All relevant SM backgrounds for the dileptonic tt¯ search at the LHC are considered. Furthermore, CP angular observables were used to probe the CP-nature of the coupling between the mediator and top-quarks, which allowed to set confidence level (CL) limits for those Yukawa couplings as a function of the mediator mass.