scholarly journals Higgs and top physics reconstruction challenges and opportunities at FCC-ee

2021 ◽  
Vol 137 (1) ◽  
Author(s):  
Patrizia Azzi ◽  
Loukas Gouskos ◽  
Michele Selvaggi ◽  
Frank Simon
Keyword(s):  
Top Quark ◽  
Clustering Algorithms ◽  
Top Physics ◽  
Z Bosons ◽  
Machine Learning Techniques ◽  
Full Potential ◽  
Final States ◽  
Precise Identification ◽  
Event Reconstruction ◽  
Quark Decay

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.

scholarly journals Top physics at the LHC

2015 ◽  
Vol 30 (35) ◽  
pp. 1530063 ◽  
Author(s):  
Vittorio Del Duca ◽  
Eric Laenen
Keyword(s):  
Top Quark ◽  
Charge Asymmetry ◽  
Top Physics ◽  
Present Situation ◽  
Top Quark Mass ◽  
Single Top ◽  
Key Concepts ◽  
Theoretical Predictions ◽  
Top Quark Decay ◽  
Quark Decay

We review the present situation in top quark physics, in these early days of Run II of the LHC. We take mostly a Standard Model perspective, showing recent results, and review the key concepts and results of the associated theoretical predictions. The issues we discuss are the top quark mass, top quark pair and single top production, production in association with other particles, charge asymmetry and top quark decay.

scholarly journals Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at $$ \sqrt{s} $$ = 13 TeV

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
◽  
N. Tonon ◽  
H. Aarup Petersen ◽  
M. Aldaya Martin ◽  
P. Asmuss ◽  
...  
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
Top Quark ◽  
Z Boson ◽  
Top Quarks ◽  
Effective Field ◽  
Machine Learning Techniques ◽  
Final States ◽  
Associated Production ◽  
Five Dimension

Abstract A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data sample corresponds to an integrated luminosity of 138 fb−1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.

scholarly journals Combine and conquer: event reconstruction with Bayesian Ensemble Neural Networks

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Jack Y. Araz ◽  
Michael Spannowsky
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Top Quark ◽  
Feature Space ◽  
Training Sample ◽  
Bayesian Techniques ◽  
Training Sample Size ◽  
Event Reconstruction ◽  
Neural Network Classifiers ◽  
Quark Jets

Abstract Ensemble learning is a technique where multiple component learners are combined through a protocol. We propose an Ensemble Neural Network (ENN) that uses the combined latent-feature space of multiple neural network classifiers to improve the representation of the network hypothesis. We apply this approach to construct an ENN from Convolutional and Recurrent Neural Networks to discriminate top-quark jets from QCD jets. Such ENN provides the flexibility to improve the classification beyond simple prediction combining methods by linking different sources of error correlations, hence improving the representation between data and hypothesis. In combination with Bayesian techniques, we show that it can reduce epistemic uncertainties and the entropy of the hypothesis by simultaneously exploiting various kinematic correlations of the system, which also makes the network less susceptible to a limitation in training sample size.

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.

MEASUREMENT OF THE TOP QUARK PAIR PRODUCTION CROSS SECTION IN LEPTON+JETS FINAL STATES AT DØ USING A MULTIVARIATE TECHNIQUE

2005 ◽  
Vol 20 (14) ◽  
pp. 3177-3179
Author(s):  
◽  
TOBIAS GOLLING
Keyword(s):  
Pair Production ◽  
Cross Section ◽  
Top Quark ◽  
Production Cross Section ◽  
Production Cross ◽  
Final States ◽  
Multivariate Technique ◽  
Text Production ◽  
Lepton Jets ◽  
Pair Production Cross Section

A measurement of the [Formula: see text] production cross-section at [Formula: see text] with the DØ detector at the Fermilab Tevatron, based on the application of a multivariate topological method is presented. The integrated luminosity corresponds to 143.9 pb-1 in the μ+jets and 141.2 pb-1 in the e+jets channel. The preliminary cross-section is measured to be [Formula: see text].

ONE-LOOP RADIATIVE CORRECTIONS TO A HEAVY TOP DECAY IN THE STANDARD MODEL

1991 ◽  
Vol 06 (27) ◽  
pp. 4925-4948 ◽  
Author(s):  
JIANG LIU ◽  
YORK-PENG YAO
Keyword(s):  
Top Quark ◽  
Asymmetry Parameter ◽  
Partial Width ◽  
Angular Distributions ◽  
Radiative Corrections ◽  
Inclusive Process ◽  
The Standard Model ◽  
Top Quark Decay ◽  
Quark Decay ◽  
Exclusive Or

We study one-loop radiative corrections to the top-quark decay: t→bW. For a heavy top (i.e. mt≳100 GeV ), simple analytic formulas are derived. For the inclusive process, t→bW+X due to QCD, cancellations of infrared and mass singularities are shown explicitly. The final result agrees with an earlier calculation in the literature, and is an 8% reduction in the partial width for αs=0.1. Also, leading terms of the electroweak corrections are shown to be proportional to an enhancement factor [Formula: see text]. Their effect is about 1-3%. We also study the angular distributions of the leptons from the subsequent exclusive (or semi-inclusive) W decay. An asymmetry parameter which measures the polarizations of the W is introduced. We find that it is sensitive to the QCD corrections especially in the vicinity of [Formula: see text].

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