Percorrer por autor "ATLAS collaboration (2827 authors)"
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- A search for an excited muon decaying to a muon and two jets in $pp$ collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detectorPublication . ATLAS collaboration (2827 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oleiro Seabra, Luis Filipe; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA new search signature for excited leptons is explored. Excited muons are sought in the channel ${pp}\to \mu {\mu }^{* }\to \mu \mu \ {\rm{jet}}\,{\rm{jet}}$, assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb(−)(1) of pp collision data at a centre-of-mass energy of $\sqrt{s}\,=\,8\,{\rm{TeV}}$ taken with the ATLAS detector at the large hadron collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass ${m}_{{\mu }^{* }}$. For ${m}_{{\mu }^{* }}$ between 1.3 and 3.0 TeV, the upper limit on $\sigma B({\mu }^{* }\to \mu q\bar{q}$) is between 0.6 and 1 fb. Limits on $\sigma B$ are converted to lower bounds on the compositeness scale Λ. In the limiting case ${\rm{\Lambda }}={m}_{{\mu }^{* }}$, excited muons with a mass below 2.8 TeV are excluded. With the same model assumptions, these limits at larger ${\mu }^{* }$ masses improve upon previous limits from traditional searches based on the gauge-mediated decay ${\mu }^{* }\to \mu \gamma $.
- Measurements of the Higgs boson production and decay rates and coupling strengths using pp collision data at $\sqrt{s}=7$ and 8 TeV in the ATLAS experimentPublication . ATLAS collaboration (2827 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutCombined analyses of the Higgs boson production and decay rates as well as its coupling strengths to vector bosons and fermions are presented. The combinations include the results of the analyses of the $H\rightarrow \gamma \gamma ,\, ZZ^*,\, WW^*,\, Z\gamma ,\, b\bar{b},\, \tau \tau $ and $\mu \mu $ decay modes, and the constraints on the associated production with a pair of top quarks and on the off-shell coupling strengths of the Higgs boson. The results are based on the LHC proton-proton collision datasets, with integrated luminosities of up to 4.7 $\mathrm {fb}^{-1}$ at $\sqrt{s}=7$ TeV and 20.3 $\mathrm {fb}^{-1}$ at $\sqrt{s}=8$ TeV, recorded by the ATLAS detector in 2011 and 2012. Combining all production modes and decay channels, the measured signal yield, normalised to the Standard Model expectation, is $1.18^{+0.15-0.14}$ . The observed Higgs boson production and decay rates are interpreted in a leading-order coupling framework, exploring a wide range of benchmark coupling models both with and without assumptions on the Higgs boson width and on the Standard Model particle content in loop processes. The data are found to be compatible with the Standard Model expectations for a Higgs boson at a mass of 125.36 GeV for all models considered.
- Search for a CP-odd Higgs boson decaying to Zh in pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detectorPublication . ATLAS collaboration (2827 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search for a heavy, CP-odd Higgs boson, A , decaying into a Z boson and a 125 GeV Higgs boson, h , with the ATLAS detector at the LHC is presented. The search uses proton–proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb −1 . Decays of CP-even h bosons to ττ or bb pairs with the Z boson decaying to electron or muon pairs are considered, as well as h→bb decays with the Z boson decaying to neutrinos. No evidence for the production of an A boson in these channels is found and the 95% confidence level upper limits derived for σ(gg→A)×BR(A→Zh)×BR(h→ff¯) are 0.098–0.013 pb for f=τ and 0.57–0.014 pb for f=b in a range of mA=220–1000 GeV . The results are combined and interpreted in the context of two-Higgs-doublet models.
- Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at $\sqrt{s}=$8 TeV with the ATLAS detectorPublication . ATLAS collaboration (2827 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutResults of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb ${}^{-1}$ of $\sqrt{s}=8$ TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with $p_{\mathrm {T}}> 120$ GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between $E_{\mathrm {T}}^{\mathrm {miss}}>150$ GeV and $E_{\mathrm {T}}^{\mathrm {miss}}> 700$ GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.
- Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detectorPublication . ATLAS collaboration (2827 authors); Aguilar-Saavedra, Juan Antonio; Amor Dos Santos, Susana Patricia; Anjos, Nuno; Araque, Juan Pedro; Cantrill, Robert; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Da Cunha Sargedas De Sousa, Mario Jose; Fiolhais, Miguel; Galhardo, Bruno; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Onofre, António; Palma, Alberto; Pedro, Rute; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Tavares Delgado, Ademar; Veloso, Filipe; Wolters, HelmutA search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb −1 of proton–proton collision data recorded by the ATLAS experiment at s=8 TeV at the Large Hadron Collider. Five final states, targeting the decays H→WW⁎ , ττ , and ZZ⁎ , are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons ( e or μ ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the tt¯H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1−1.2+1.4 times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p -value for compatibility with the background-only hypothesis is 1.8 σ ; the expectation in the presence of a Standard Model signal is 0.9 σ .