Probing anomalous Wtb couplings in top pair decays

We discuss new physics in top-quark interactions, using an effective field theory approach. We consider top-quark decay, single top production, and top-quark pair production. We identify 15 dimension-six operators that contribute to these processes, and we compute the deviation from the Standard Model induced by these operators. The results provide a systematic way of searching for (or obtaining bounds on) physics beyond the Standard Model.

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“…Furthermore, both the angular distribution and energy distribution can be expressed using the W helicity fractions [22]:…”

Section: Top Quark Decaymentioning

confidence: 99%

Effective-field-theory approach to top-quark production and decay

2011

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“…In the template method W helicity fractions are extracted from the binned Poisson likelihood fit to data of the sum of background and right-handed, left-handed, and longitudinal helicity templates for the signal. The Monte Carlo generator Protos [6] was used to generate three samples with F 0 = 1, F L = 1 and F R = 1. This was achieved by choosing appropriate values for anomalous Wtb couplings [6].…”

Section: Results From the Lhcmentioning

confidence: 99%

“…The Monte Carlo generator Protos [6] was used to generate three samples with F 0 = 1, F L = 1 and F R = 1. This was achieved by choosing appropriate values for anomalous Wtb couplings [6]. The measured values of F 0 , F L and F R after combining dilepton and + jets channels are: F 0 = 0.66±0.06(stat)±0.07(syst), F L = 0.33±0.03(stat)± 0.03(syst), F R = 0.01 ± 0.03(stat) ± 0.06(syst).…”

Section: Results From the Lhcmentioning

confidence: 99%

W helicity, top quark spin and charge

Shabalina

2013

EPJ Web of Conferences

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Abstract. An overview of the recent measurements of top quark charge, spin correlations, and top quark and W boson polarisation in tt events is presented. The measurements were performed at the Fermilab Tevatron collider in pp collision data at √ s = 1.96 TeV by the CDF and D0 experiments and in pp collision data at √ s = 7 TeV by the ATLAS and CMS experiments IntroductionThe existence of the top quark was required in the Standard Model (SM) as an isospin partner of the b-quark with its properties well defined expect for the mass. When top quark was discovered at the Fermilab Tevatron in 1995 [1] its mass appeared to be the largest of known fundamental particles and it makes this particle unique. The lifetime of the top quark, inspite being determined by the weak interactions, is at least an order of magnitude shorter than the time scale for strong interactions, implying that the top quark decays before hadronization [2] and thus its properties can be studied from the distributions of the decay products. Given precise predictions by the SM measurements of top quark properties play an important role in proving the validity of SM and can give a hint for new physics if deviations are found. Studies of the top quark properties started at the Tevatron but were severely statistically limited until recently when the full Tevatron dataset became available. The LHC with its high rate of top pair production provides a unique opportunity to perform precision measurements of the top quark production and decay properties.Within the SM, top quark decays to a W boson and a b-quark with nearly 100% probability. Thus, tt events can create final states with two leptons (dilepton channel) if both W bosons from top quark decay leptonically into eν e , µν µ or τν τ , single lepton ( + jets channel) with one W boson decaying leptonically and another one hadronically into qq , or no leptons (all hadronic channel) if both W bosons decay hadronically. The dilepton and single lepton channels are typically used to study top quark properties due to their clean signatures and manageable backgrounds.The + jets channel is characterized by one high transverse momentum (p T ) charged isolated lepton (e or µ), large missing transverse momentum from the neutrino escaping the detector, and at least four jets, two of which originate from b-quarks. Properties measurements performed in this channel typically require at least one or two a e-mail: Elizaveta.Shabalina@cern.ch jets identified as b-jets by a b-tagging algorithm to supress the main background coming from W production in association with jets.The dilepton tt signal is characterized by two high-p T isolated charged leptons, missing transverse momentum corresponding to the undetected neutrinos from the two leptonically decaying W bosons, and two b-jets. Due to the small backgrounds dominated by the Z+jets and diboson production this channel offers an opportunity to study top quark properties without a b-tagged jet requirement to avoid the associated systematic uncertainty. W boson helicityThe...

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“…The first measurement performs a template fit of the sum of the three helicity states to the cosθ * distribution. The templates were produced with the Protos MC generator [20], each with a longitudinal, left-, and right-handed helicity of 1. The fit to data is shown in Figure 8 in the lepton + jets channel, where the SM expectation of the helicity states is compared to the best fit to data along with the uncertainties.…”

Section: W Tb Vertex Measurementmentioning

confidence: 99%

Measurement of the Top Quark Properties with the ATLAS Detector

Guindon

2013

EPJ Web of Conferences

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Abstract. The top quark, discovered at the Tevatron in 1995 by the CDF and DØ collaborations, is the heaviest known particle. The measurement of its properties are of interest to the understanding of the strong and weak forces, as well as searches for physics beyond the Standard Model. Several measurements of top quark properties are presented using data collected at the ATLAS experiment located at the Large Hadron Collider (LHC) at √ s = 7 TeV centre-of-mass energy. The measurements include top quark polarisation, spin correlation, production of ttZ and ttγ, as well as top mass and W tb vertex measurements in both the lepton + jets and dilepton channel.

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Probing anomalous Wtb couplings in top pair decays

Cited by 134 publications

References 39 publications

Effective-field-theory approach to top-quark production and decay

Effective-field-theory approach to top-quark production and decay

W helicity, top quark spin and charge

Measurement of the Top Quark Properties with the ATLAS Detector

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