Spinning the top quark

Falkowski, Adam; Pérez, Gilad; Schmaltz, Martin

doi:10.1103/physrevd.87.034041

Cited by 27 publications

(48 citation statements)

References 49 publications

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“…1. In [60][61][62][63][64][65][66][67][68][69][70][71], comparisons between different models are carried out, and study of those models or measurements in the LHC context can be found in [72][73][74][75][76][77][78][79][80][81][82][83][84].…”

Section: Introductionmentioning

confidence: 99%

Diagnosing the top-quark angular asymmetry using LHC intrinsic charge asymmetries

2012

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Flavor-violating interactions involving new heavy particles are among proposed explanations for the tt forward-backward asymmetry observed at the Tevatron. Many of these models generate a tt-plus-jet signal at the LHC. In this paper we identify several new charge asymmetric variables in ttj events that can contribute to the discovery of such models at the LHC. We propose a data-driven method for the background, largely eliminating the need for a Monte Carlo prediction of tt-plus-jets, and thus reducing systematic errors. With a fast detector simulation, we estimate the statistical sensitivity of our variables for one of these models, finding that charge-asymmetric variables could materially assist in the exclusion of the Standard Model across much of the mass and coupling range, given 5 inverse fb of data. Should any signal appear, our variables will be useful in distinguishing classes of models from one another.

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Section: Introductionmentioning

confidence: 99%

Diagnosing the top-quark angular asymmetry using LHC intrinsic charge asymmetries

2012

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“…The fact that neither the Tevatron nor the Large Hadron Collider (LHC) have observed any other anomaly in top or jet physics sets strong constraints on possible explanations in terms of new physics [3][4][5]. One of the few surviving explanations, compatible with the present measurements of the tt invariant mass spectrum [6] and the charge asymmetry at the LHC [7, 8], is a relatively light colour octet vector boson (called here 'gluon' for brevity) with mass M 1 TeV and with suppressed axial-vector couplings to the light quarks and sizeable axial-vector couplings to top quarks [9][10][11][12][13][14][15][16][17]. The axial coupling ensures cancelation of the interference terms between the SM and new physics contribution [18][19][20] in symmetric observables while preserving the contribution to the asymmetry.…”

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confidence: 83%

Four top quarks and thett¯forward-backward asymmetry

Aguilar-Saavedra

Santiago

2012

Phys. Rev. D

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New colour octet vectors below the TeV scale could explain the anomalous tt forward-backward asymmetry observed at the Tevatron experiments, while being consistent with the current LHC data. These models generally lead to four-top final states at the LHC at observable levels. We compute the four-top production cross section at the LHC in a model with a massive colour octet vector as a function its mass, its width and its coupling to the top quark. Octet masses in the vicinity of the tt threshold are generally excluded by present limits on the production of same-sign dileptons and trileptons. Masses above 650 GeV are allowed, quite independently of the couplings, but they can be probed with the luminosity of 5 fb −1 already collected at the LHC, up to around 800 GeV. The four-top production cross section is increased by a factor ∼ 2 with √ s = 8 TeV and by up to almost two orders of magnitude with √ s = 14 TeV, thus greatly increasing the reach for massive gluons after the LHC energy upgrade.Due to its large mass, the top quark is expected to play a relevant role in the discovery of new physics beyond the Standard Model (SM). The first hint of such new physics could be already available in the form of the anomalously large tt forward-backward (FB) asymmetry observed at both Tevatron experiments [1,2]. The fact that neither the Tevatron nor the Large Hadron Collider (LHC) have observed any other anomaly in top or jet physics sets strong constraints on possible explanations in terms of new physics [3][4][5]. One of the few surviving explanations, compatible with the present measurements of the tt invariant mass spectrum [6] and the charge asymmetry at the LHC [7, 8], is a relatively light colour octet vector boson (called here 'gluon' for brevity) with mass M 1 TeV and with suppressed axial-vector couplings to the light quarks and sizeable axial-vector couplings to top quarks [9][10][11][12][13][14][15][16][17]. The axial coupling ensures cancelation of the interference terms between the SM and new physics contribution [18][19][20] in symmetric observables while preserving the contribution to the asymmetry. Masses around 1 TeV require large couplings to the top quark and a large gluon width, usually with extra decay channels [11]. Masses close to the tt threshold can easily hide in the large SM tt background, although they may also need extra decay channels to be invisible [12]. Masses lighter than the tt threshold can do with smaller couplings and are essentially invisible in symmetric observables [14].In this paper we consider an alternative, yet unexplored probe of these models. The massive gluon is a colour octect vector resonance, thus its couplings to SM gluons are fixed by gauge invariance. Due to the relatively low masses relevant for the FB asymmetry, pair production of such objects with subsequent decay in two top pairs can receive a fairly large cross section, which is further increased by non-resonant contributions and by single gluon resonant production, especially if the coupling of the new gluon to t...

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“…In particular, the lepton-based asymmetry near the tt threshold directly probes the chiralities of the initial qq pair [126]. Since NP A FB contributions here originate from RH up quark/antiquark collisions, a negative contribution to the leptonbased asymmetry is expected near threshold.…”

Section: Bottom and Lepton-based Top A Fb At The Tevatronmentioning

confidence: 99%

“…The forward-backward charged lepton (or lepton-based) asymmetry in tt production at the Tevatron is a useful discriminant in order to better characterize the NP source explaining the top A FB [124][125][126][127][128][129]. In particular, the lepton-based asymmetry near the tt threshold directly probes the chiralities of the initial qq pair [126].…”

Section: Bottom and Lepton-based Top A Fb At The Tevatronmentioning

confidence: 99%

Up asymmetries from exhilarated composite flavor structures

Rold

Delaunay

Grojean

et al. 2013

J. High Energ. Phys.

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We present a class of warped extra dimension (composite Higgs) models which conjointly accommodates the tt forward-backward asymmetry observed at the Tevatron and the direct CP asymmetry in singly Cabibbo suppressed D decays first reported by the LHCb collaboration. We argue that both asymmetries, if arising dominantly from new physics beyond the Standard Model, hint for a flavor paradigm within partial compositeness models in which the right-handed quarks of the first two generations are not elementary fields but rather composite objects. We show that this class of models is consistent with current data on flavor and CP violating physics, electroweak precision observables, dijet and top pair resonance searches at hadron colliders. These models have several predictions which will be tested in forthcoming experiments. The CP asymmetry in D decays is induced through an effective operator of the form (ūc) V +A (ss) V +A at the charm scale, which implies a larger CP asymmetry in the D 0 → K + K − rate relative the D 0 → π + π − channel. This prediction is distinctive from other Standard Model or dipole-based new physics interpretation of the LHCb result. CP violation in D−D mixing as well as an an excess of dijet production of the LHC are also predicted to be observed in a near future. A large top asymmetry originates from the exchange of an axial resonance which dominantly produces left-handed top pairs. As a result a negative contribution to the lepton-based forward-backward asymmetry in tt production, as well as O(10%) forward-backward asymmetry in bb production above m bb ≃ 600 GeV at the Tevatron is expected.

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Spinning the top quark

Cited by 27 publications

References 49 publications

Diagnosing the top-quark angular asymmetry using LHC intrinsic charge asymmetries

Diagnosing the top-quark angular asymmetry using LHC intrinsic charge asymmetries

Four top quarks and thett¯forward-backward asymmetry

Up asymmetries from exhilarated composite flavor structures

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