quark decay
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2021 ◽  
Vol 137 (1) ◽  
Author(s):  
Patrizia Azzi ◽  
Loukas Gouskos ◽  
Michele Selvaggi ◽  
Frank Simon

AbstractThe Higgs bosons and the top quark decay into rich and diverse final states, containing both light and heavy quarks, gluons, photons as well as W and Z bosons. This article reviews the challenges involved in reconstructing Higgs and top events at the FCC-ee and identifies the areas where novel developments are needed. The precise identification and reconstruction of these final states at the FCC-ee rely on the capability of the detector to provide excellent flavour tagging, jet energy and angular resolution, and global kinematic event reconstruction. Excellent flavour tagging performance requires low-material vertex and tracking detectors, and advanced machine learning techniques as successfully employed in LHC experiments. In addition, the Z pole run will provide abundant samples of heavy flavour partons that can be used for calibration of the tagging algorithms. For the reconstruction of jets, leptons, and missing energy, particle-flow algorithms are crucial to explore the full potential of the highly granular tracking and calorimeter systems, and give access to excellent energy–momentum resolution and precise identification of heavy bosons in their hadronic decays. This enables, among many other key elements, the reconstruction of Higgsstrahlung processes with leptonically and hadronically decaying Z bosons, and an almost background-free identification of top quark pair events. Exploiting the full available kinematic constraints together with exclusive jet clustering algorithms will allow for the optimisation of global event reconstruction with kinematic fitting techniques.


2021 ◽  
Vol 104 (11) ◽  
Author(s):  
Peng-Cheng Lu ◽  
Zong-Guo Si ◽  
Zhe Wang ◽  
Xing-Hua Yang

Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2319
Author(s):  
Abdesslam Arhrib ◽  
Rachid Benbrik ◽  
Mohamed Krab ◽  
Bouzid Manaut ◽  
Stefano Moretti ◽  
...  

A light charged Higgs boson has been searched for at the Large Hadron Collider (LHC) via top (anti)quark decay, i.e., t→bH+, if kinematically allowed. In this contribution, we propose new channels for light charged Higgs boson searches via the pair productions pp→H±h/A and pp→H+H− at the LHC in the context of the Two-Higgs Doublet Model (2HDM) Type-I. By focusing on a case where the heavy H state is the Standard Model (SM)-like one already observed, we investigate the production of the aforementioned charged Higgs bosons and their bosonic decay channels, namely, H±→W±h and/or H±→W±A. We demonstrate that such production and decay channels can yield substantial alternative discovery channels for H± bosons at the LHC. Finally, we propose eight benchmark points (BPs) to motivate the search for such signatures.


2021 ◽  
Vol 822 ◽  
pp. 136704
Author(s):  
S. Slabospitskii

2021 ◽  
Vol 104 (7) ◽  
Author(s):  
Ben Carlson ◽  
Tao Han ◽  
Sze Ching Iris Leung

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Giuseppe Bevilacqua ◽  
Huan-Yu Bi ◽  
Heribertus Bayu Hartanto ◽  
Manfred Kraus ◽  
Michele Lupattelli ◽  
...  

Abstract We report on the calculation of the next-to-leading order QCD corrections to the production of a $$ t\overline{t} $$ t t ¯ pair in association with two heavy-flavour jets. We concentrate on the di-lepton $$ t\overline{t} $$ t t ¯ decay channel at the LHC with $$ \sqrt{s} $$ s = 13 TeV. The computation is based on pp → e+νeμ−$$ \overline{\nu} $$ ν ¯ μ$$ b\overline{b}b\overline{b} $$ b b ¯ b b ¯ matrix elements and includes all resonant and non-resonant diagrams, interferences and off-shell effects of the top quark and the W gauge boson. As it is customary for such studies, results are presented in the form of inclusive and differential fiducial cross sections. We extensively investigate the dependence of our results upon variation of renormalisation and factorisation scales and parton distribution functions in the quest for an accurate estimate of the theoretical uncertainties. We additionally study the impact of the contributions induced by the bottom-quark parton density. Results presented here are particularly relevant for measurements of $$ t\overline{t}H $$ t t ¯ H (H → $$ b\overline{b} $$ b b ¯ ) and the determination of the Higgs coupling to the top quark. In addition, they might be used for precise measurements of the top-quark fiducial cross sections and to investigate top-quark decay modelling at the LHC.


2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Giuseppe Bevilacqua ◽  
Huan-Yu Bi ◽  
Heribertus Bayu Hartanto ◽  
Manfred Kraus ◽  
Jasmina Nasufi ◽  
...  

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.


2021 ◽  
Vol 103 (11) ◽  
Author(s):  
Michał Czakon ◽  
Andrzej Czarnecki ◽  
Matthew Dowling
Keyword(s):  

2021 ◽  
pp. 136375
Author(s):  
I. Turk Cakir ◽  
O. Cakir ◽  
H. Denizli ◽  
A. Senol ◽  
A. Yilmaz

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Alexander Lenz ◽  
Maria Laura Piscopo ◽  
Aleksey V. Rusov

Abstract We compute the Darwin operator contribution ($$ 1/{m}_b^3 $$ 1 / m b 3 correction) to the width of the inclusive non-leptonic decay of a B meson (B+, Bd or Bs), stemming from the quark flavour-changing transition b → $$ {q}_1{\overline{q}}_2{q}_3 $$ q 1 q ¯ 2 q 3 , where q1, q2 = u, c and q3 = d, s. The key ideas of the computation are the local expansion of the quark propagator in the external gluon field including terms with a covariant derivative of the gluon field strength tensor and the standard technique of the Heavy Quark Expansion (HQE). We confirm the previously known expressions of the $$ 1/{m}_b^3 $$ 1 / m b 3 contributions to the semi-leptonic decay b → $$ {q}_1\mathrm{\ell}{\overline{\nu}}_{\mathrm{\ell}} $$ q 1 ℓ ν ¯ ℓ , with ℓ = e, μ, τ and of the $$ 1/{m}_b^2 $$ 1 / m b 2 contributions to the non-leptonic modes. We find that this new term can give a sizeable correction of about −4 % to the non-leptonic decay width of a B meson. For Bd and Bs mesons this turns out to be the dominant correction to the free b-quark decay, while for the B+ meson the Darwin term gives the second most important correction — roughly 1/2 to 1/3 of the phase space enhanced Pauli interference contribution. Due to the tiny experimental uncertainties in lifetime measurements the incorporation of the Darwin term contribution is crucial for precision tests of the Standard Model.


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