scholarly journals Two-loop electroweak corrections to the Top-Quark Contribution to ϵK

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Joachim Brod ◽  
Sandra Kvedaraitė ◽  
Zachary Polonsky
Keyword(s):  
Top Quark ◽  
New Physics ◽  
Neutral Kaon ◽  
Quark Contribution ◽  
Input Parameters ◽  
Global Fit ◽  
Theory Uncertainty ◽  
Electroweak Corrections

Abstract The parameter ϵK measures CP violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. The perturbative theory uncertainty is currently dominated by the top-quark contribution. Here, we present the calculation of the full two-loop electroweak corrections to the top-quark contribution to ϵK, including the resummation of QED-QCD logarithms. We discuss different renormalization prescriptions for the electroweak input parameters. In the traditional normalization of the weak Hamiltonian with two powers of the Fermi constant GF, the top-quark contribution is shifted by −1%.

scholarly journals Indirect $$ \mathcal{CP} $$ probes of the Higgs-top-quark interaction: current LHC constraints and future opportunities

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Henning Bahl ◽  
Philip Bechtle ◽  
Sven Heinemeyer ◽  
Judith Katzy ◽  
Tobias Klingl ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Top Quark ◽  
Decay Channel ◽  
New Physics ◽  
Current Data ◽  
Quark Interaction ◽  
The Standard Model ◽  
Vector Bosons ◽  
Selection Of

Abstract The $$ \mathcal{CP} $$ CP structure of the Higgs boson in its coupling to the particles of the Standard Model is amongst the most important Higgs boson properties which have not yet been constrained with high precision. In this study, all relevant inclusive and differential Higgs boson measurements from the ATLAS and CMS experiments are used to constrain the $$ \mathcal{CP} $$ CP -nature of the top-Yukawa interaction. The model dependence of the constraints is studied by successively allowing for new physics contributions to the couplings of the Higgs boson to massive vector bosons, to photons, and to gluons. In the most general case, we find that the current data still permits a significant $$ \mathcal{CP} $$ CP -odd component in the top-Yukawa coupling. Furthermore, we explore the prospects to further constrain the $$ \mathcal{CP} $$ CP properties of this coupling with future LHC data by determining tH production rates independently from possible accompanying variations of the $$ t\overline{t}H $$ t t ¯ H rate. This is achieved via a careful selection of discriminating observables. At the HL-LHC, we find that evidence for tH production at the Standard Model rate can be achieved in the Higgs to diphoton decay channel alone.

scholarly journals Erratum to: The electro-weak couplings of the top and bottom quarks — global fit and future prospects

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Gauthier Durieux ◽  
Adrian Irles ◽  
Víctor Miralles ◽  
Ana Peñuelas ◽  
Martín Perelló ◽  
...  
Keyword(s):  
Top Quark ◽  
Current Data ◽  
Bottom Quarks ◽  
Future Prospects ◽  
Quark Decays ◽  
Global Fit

In the course of follow-up work a mistake was discovered in the parameterization of the dependence of the W-boson helicity fractions in top quark decays. The dependence on two operator coefficients, Cφtb and CbW, was erroneously omitted. Inclusion of this dependence leads to significantly stronger bounds on these operators from the current data and modifies also the HL-LHC prospects. The expectations for e+e− colliders are not affected. We present corrected results in this erratum.

scholarly journals Infrared renormalons in collider processes

2021 ◽  
Author(s):  
Silvia Ferrario Ravasio
Keyword(s):  
Top Quark ◽  
Particle Physics ◽  
Theoretical Calculations ◽  
Accurate Determination ◽  
New Physics ◽  
Operator Product ◽  
Power Correction ◽  
Collider Phenomenology ◽  
Power Corrections ◽  
Decay Products

AbstractPrecise theoretical predictions are a key ingredient for an accurate determination of the structure of the Lagrangian of particle physics, including its free parameters, which summarizes our understanding of the fundamental interactions among particles. Furthermore, due to the absence of clear new-physics signals, precise theoretical calculations are required to pin down possible subtle deviations from the Standard Model predictions. The error associated with such calculations must be scrutinized, as non-perturbative power corrections, dubbed infrared renormalons, can limit the ultimate precision of truncated perturbative expansions in quantum chromodynamics. In this review, we focus on linear power corrections that can arise in certain kinematic distributions relevant for collider phenomenology where an operator product expansion is missing, e.g. those obtained from the top-quark decay products, shape observables and the transverse momentum of massive gauge bosons. Only the last one is found to be free from such corrections, while the mass of the system comprising the top decay products has a larger power correction if the perturbative expansion is expressed in terms of a short-distance mass instead of the pole mass. A proper modelization of non-perturbative corrections is crucial in the context of shape observables to obtain reliable strong coupling constant extractions.

scholarly journals NLO QCD corrections to off-shell $${t{\bar{t}}W^\pm }$$ production at the LHC: correlations and asymmetries

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Giuseppe Bevilacqua ◽  
Huan-Yu Bi ◽  
Heribertus Bayu Hartanto ◽  
Manfred Kraus ◽  
Jasmina Nasufi ◽  
...  
Keyword(s):  
Top Quark ◽  
Charge Asymmetry ◽  
New Physics ◽  
Atlas Collaboration ◽  
Narrow Width Approximation ◽  
Theoretical Predictions ◽  
Top Quark Decay ◽  
Quark Decay ◽  
Precision Observables ◽  
The Impact

AbstractRecent discrepancies between theoretical predictions and experimental data in multi-lepton plus b-jets analyses for the $$t{\bar{t}}W^\pm $$ t t ¯ W ± process, as reported by the ATLAS collaboration, have indicated that more accurate theoretical predictions and high precision observables are needed to constrain numerous new physics scenarios in this channel. To this end we employ NLO QCD computations with full off-shell top quark effects included to provide theoretical predictions for the $$\mathcal{R}= \sigma _{t{\bar{t}}W^+}/\sigma _{t{\bar{t}}W^-}$$ R = σ t t ¯ W + / σ t t ¯ W - cross section ratio at the LHC with $$\sqrt{s}=13$$ s = 13 TeV. Depending on the transverse momentum cut on the b-jet we obtain 2–3% theoretical precision on $$\mathcal{R}$$ R , which should help to shed some light on new physics effects that can reveal themselves only once sufficiently precise Standard Model theoretical predictions are available. Furthermore, triggered by these discrepancies we reexamine the charge asymmetry of the top quark and its decay products in the $$t{\bar{t}}W^\pm $$ t t ¯ W ± production process. In the case of charge asymmetries, that are uniquely sensitive to the chiral nature of possible new physics in this channel, theoretical uncertainties below 15% are obtained. Additionally, the impact of the top quark decay modelling is scrutinised by explicit comparison with predictions in the narrow-width approximation.

scholarly journals tt̄H Coupling Measurement with the ATLAS Detector at the LHC

2018 ◽  
Vol 182 ◽  
pp. 02052
Author(s):  
Asma Hadef
Keyword(s):  
Higgs Boson ◽  
Cross Sections ◽  
Top Quark ◽  
High Energy Physics ◽  
Center Of Mass ◽  
High Energy ◽  
New Physics ◽  
Decay Modes ◽  
Center Of Mass Energy ◽  
Higgs Decay

The Higgs boson was discovered on the 4th of July 2012 with a mass around 125 GeV by ATLAS and CMS experiments at LHC. Determining the Higgs properties (production and decay modes, couplings,...) is an important part of the high-energy physics programme in this decade. A search for the Higgs boson production in association with a top quark pair (tt̄H) at ATLAS [1] is summarized in this paper at an unexplored center-of-mass energy of 13 TeV, which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The tt̄H analysis in ATLAS is divided into 3 channels according to the Higgs decay modes: H → Hadrons, H → Leptons and H → Photons. The best-fit value of the ratio of observed and Standard Model cross sections of tt̄H production process, using 2015-2016 data and combining all tt̄H final states, is 1:8±0:7, corresponds to 2:8σ (1:8σ) observed (expected) significance.

Top quark at the upgraded Tevatron to prove new physics

1998 ◽  
Author(s):  
Jin Min Yang ◽  
A. Datta ◽  
M. Hosch ◽  
C. S. Li ◽  
R. J. Oakes ◽  
...  
Keyword(s):  
Top Quark ◽  
New Physics
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