Browsing by Author "ATLAS collaboration (2920 authors)"
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- A search for lepton-flavor-violating decays of the $Z$ boson into a $\tau$-lepton and a light lepton with the ATLAS detectorPublication . ATLAS collaboration (2920 authors); Aguilar Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Araque Espinosa, Juan Pedro; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Dias DO Vale, Tiago; Faisca Rodrigues Pereira, Rui Miguel; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Mendes Gouveia, Emanuel Demetrio; Oleiro Seabra, Luis Filipe; Onofre, Antonio; Costa Batalha Pedro, Rute; Pereira Peixoto, Ana Paula; Santos, Helena; Saraiva, Joao; Silva, Jose Manuel; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutDirect searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying τ lepton are considered. The searches are based on a data sample of proton-proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1 at a center-of-mass energy of s=13 TeV. No statistically significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: B(Z→eτ)<5.8×10-5 and B(Z→μτ)<2.4×10-5. This is the first limit on B(Z→eτ) with ATLAS data. The upper limit on B(Z→μτ) is combined with a previous ATLAS result based on 20.3 fb-1 of proton-proton collision data at a center-of-mass energy of s=8 TeV and the combined upper limit at 95% confidence level is B(Z→μτ)<1.3×10-5.
- Combined measurement of differential and total cross sections in the $H \rightarrow \gamma \gamma$ and the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channels at $\sqrt{s} = 13$ TeV with the ATLAS detectorPublication . ATLAS collaboration (2920 authors); Aguilar Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Araque Espinosa, Juan Pedro; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Dias DO Vale, Tiago; Faisca Rodrigues Pereira, Rui Miguel; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Mendes Gouveia, Emanuel Demetrio; Oleiro Seabra, Luis Filipe; Onofre, Antonio; Costa Batalha Pedro, Rute; Pereira Peixoto, Ana Paula; Santos, Helena; Saraiva, Joao; Silva, Jose Manuel; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb$^{-1}$ of 13 TeV proton-proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ^* \rightarrow 4\ell$ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0$^{+6.0}_{-5.9}$ (stat.) $^{+4.0}_{-3.3}$ (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions.
- Measurement of the production cross section of jets in association with a Z boson in pp collisions at $\sqrt{s}$ = 7 TeV with the ATLAS detectorPublication . ATLAS collaboration (2920 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Do Valle Wemans, André; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oliveira, Miguel Alfonso; Onofre, António; Palma, Alberto; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Veloso, Filipe; Wolters, HelmutMeasurements of the production of jets of particles in association with a Z boson in pp collisions at $\sqrt{s}$ = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6/fb collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum pT > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton showers.
- Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in $\sqrt{s} = 13$ $\mathrm{TeV}$ $pp$ collisions with the ATLAS detectorPublication . ATLAS collaboration (2920 authors); Aguilar Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Araque Espinosa, Juan Pedro; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Dias DO Vale, Tiago; Faisca Rodrigues Pereira, Rui Miguel; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Mendes Gouveia, Emanuel Demetrio; Oleiro Seabra, Luis Filipe; Onofre, Antonio; Costa Batalha Pedro, Rute; Pereira Peixoto, Ana Paula; Santos, Helena; Saraiva, Joao; Silva, Jose Manuel; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search for the bb¯ decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channels and a photon-associated channel. Results are reported from the analysis of up to 30.6 fb-1 of pp data at s=13 TeV collected with the ATLAS detector at the LHC. The measured signal strength relative to the Standard Model prediction from the combined analysis is 2.5-1.3+1.4 for inclusive Higgs boson production and 3.0-1.6+1.7 for vector-boson fusion production only.
- Search for long-lived particles in final states with displaced dimuon vertices in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detectorPublication . ATLAS collaboration (2920 authors); Aguilar Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Araque Espinosa, Juan Pedro; Castro, Nuno Filipe; Conde Muino, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Dias DO Vale, Tiago; Faisca Rodrigues Pereira, Rui Miguel; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Goncalo, Ricardo; Jorge, Pedro; Machado Miguens, Joana; Maio, Amelia; Maneira, Jose; Mendes Gouveia, Emanuel Demetrio; Oleiro Seabra, Luis Filipe; Onofre, Antonio; Costa Batalha Pedro, Rute; Pereira Peixoto, Ana Paula; Santos, Helena; Saraiva, Joao; Silva, Jose Manuel; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9 fb$^{-1}$. No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, $H$, to a pair of dark photons, $Z_D$. Lifetimes in the range c$\tau$ = 1-2400 cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300 GeV to 1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the $Z_D$ and the Standard Model $Z$ boson versus the $Z_D$ mass (in the range 20-60 GeV), for various assumptions for the $H\rightarrow Z_D Z_D$ branching fraction.