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Featured researches published by F. Veloso.


European Physical Journal C | 2007

Probing anomalous Wtb couplings in top pair decays

Juan Antonio Aguilar-Saavedra; J. Carvalho; N. F. Castro; A. Onofre; F. Veloso

We investigate several quantities, defined in the decays of top quark pairs, which can be used to explore non-standard Wtb interactions. Two new angular asymmetries are introduced in the leptonic decay of top (anti)quarks. Both are very sensitive to anomalous Wtb couplings, and their measurement allows for a precise determination of the W helicity fractions. We also examine other angular and energy asymmetries, the W helicity fractions and their ratios, as well as spin correlation asymmetries, analysing their dependence on anomalous Wtb couplings and identifing the quantities which are most sensitive to them. It is explicitly shown that spin correlation asymmetries are less sensitive to new interactions in the decay of the top quark; therefore, when combined with the measurement of other observables, they can be used to determine the tt̄ spin correlation even in the presence of anomalous Wtb couplings. We finally discuss some asymmetries which can be used to test CP violation in tt̄ production and complex phases in the effective Wtb vertex.


European Physical Journal C | 2008

ATLAS sensitivity to Wtb anomalous couplings in top quark decays

Juan Antonio Aguilar-Saavedra; J. Carvalho; N. F. Castro; A. Onofre; F. Veloso

We study the sensitivity of the ATLAS experiment to Wtb anomalous couplings in top pair production with semileptonic decay, pp→tt̄→W+bW-b̄ with one of the W bosons decaying leptonically and the other hadronically. Several observables are examined, including the W helicity fractions and new quantities recently introduced, such as the ratios of helicity fractions and some angular asymmetries defined in the W rest frame. The dependence on anomalous couplings of all these observables has been previously obtained. In this work we show that some of the new observables also have smaller systematic uncertainties than the helicity fractions, with a similar or stronger dependence on anomalous couplings. Consequently, their measurement can significantly improve the limits on anomalous couplings. Moreover, the most sensitive measurements can be combined. In this case, the precision achieved in the determination of Wtb anomalous couplings can be of a few percent in the semileptonic channel alone.


European Physical Journal C | 2007

Study of ATLAS sensitivity to FCNC top decays

J. Carvalho; N. F. Castro; L. Chikovani; T. Djobava; J. Dodd; S. McGrath; A. Onofre; J. Parsons; F. Veloso

The ATLAS experiment sensitivity to top quark flavour changing neutral current (FCNC) decays was studied at LHC using tt̄ events. While one of the top quarks is expected to follow the dominant Standard Model decay t→bW, the other decays through a FCNC channel, i.e. t→Zu(c), t→γu(c) or t→gu(c). Different types of analyses, applied to each FCNC decay mode, were compared. The FCNC branching ratio sensitivity (assuming a 5σ signal significance) and 95% confidence level limits on the branching ratios (in the hypothesis of signal absence) were obtained.


Il Nuovo Cimento B | 2008

Study of ATLAS sensitivity to FCNC top quark decays

F. Veloso


Archive | 2012

Even bigger data: preparing for the LHC/ATLAS upgrade

Vítor Oliveira; António Manuel Silva Pina; Nuno F. Castro; A. Onofre; F. Veloso


Il Nuovo Cimento B | 2008

Top quark properties: Prospects at ATLAS

F. Veloso


Il Nuovo Cimento B | 2008

ATLAS sensitivity to Wtb anomalous couplings in t t events

Juan Antonio Aguilar-Saavedra; Joel C. Carvalho; Nuno Filipe Castro; A. Onofre; F. Veloso


Archive | 2001

Search for Single Top Production at LEP via Four-Fermion Contact Interactions at

S. Andringa; N. F. Castro; P. Gon; O. Oliveira; A. Onofre; L. Peralta; M. Pimenta; B. Tom; F. Veloso; Mendes Pinheiro

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A. Onofre

University of Coimbra

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N. F. Castro

Instituto Superior Técnico

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T. Djobava

Tbilisi State University

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