scholarly journals Testing new physics models by top charge asymmetry and polarization at the LHC

2012 ◽  
Vol 85 (1) ◽  
Author(s):  
Junjie Cao ◽  
Kenichi Hikasa ◽  
Lin Wang ◽  
Lei Wu ◽  
Jin Min Yang
Keyword(s):  
Charge Asymmetry ◽  
New Physics

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 EFFECT OF BOTH Z AND Z′-MEDIATED FLAVOR-CHANGING NEUTRAL CURRENTS ON Bs →τ+τ- DECAY

2012 ◽  
Vol 27 (31) ◽  
pp. 1250184 ◽  
Author(s):  
S. SAHOO ◽  
D. BANERJEE ◽  
M. KUMAR ◽  
S. MOHANTY
Keyword(s):  
Cp Violation ◽  
Standard Model ◽  
Rare Decay ◽  
Charge Asymmetry ◽  
Branching Ratio ◽  
New Physics ◽  
Neutral Currents ◽  
Flavor Changing ◽  
Potential Source ◽  
Flavor Changing Neutral Currents

In recent years, Bs →τ+τ- rare decay has attracted a lot of attention since it is very sensitive to the structure of standard model (SM) and potential source of new physics beyond SM. In this paper, we study the effect of both Z and Z′-mediated flavor-changing neutral currents on the Bs →τ+τ- decay. We find the branching ratio B(Bs→τ+τ-) is enhanced relative to SM prediction, which would help to explain the recently observed CP-violation from like-sign dimuon charge asymmetry in the B system.

scholarly journals Charge Asymmetry in Top Quark Pair Production

Symmetry ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1278
Author(s):  
Roman Lysák
Keyword(s):  
Elementary Particle ◽  
Pair Production ◽  
Top Quark ◽  
Charge Asymmetry ◽  
New Physics ◽  
Current Theory ◽  
Elementary Particles ◽  
Standard Deviations ◽  
Theoretical Side

The top quark is the heaviest elementary particle known. It has been proposed many times that new physics beyond the current theory of elementary particles may reveal itself in top quark interactions. The charge asymmetry in the pair production of a fermion and its antiparticle has been known for many decades. Early measurements of such asymmetry in top quark pair production showed a disagreement with the prediction by more than 3 standard deviations. Many years of an effort on both experimental and theoretical side have allowed to understand the top quark pair charge asymmetry better and to bring back the agreement between the measurements and the theory. In this article, these efforts are reviewed together with the discussion about a potential future of such measurements.

scholarly journals THE EFFECT OF Z′ BOSON ON SAME-SIGN DIMUON CHARGE ASYMMETRY IN $B_q^0-\overline{B_q^0}$ SYSTEM

2013 ◽  
Vol 28 (15) ◽  
pp. 1350060 ◽  
Author(s):  
S. SAHOO ◽  
M. KUMAR ◽  
D. BANERJEE
Keyword(s):  
Model Prediction ◽  
Z Boson ◽  
Recent Observation ◽  
Standard Model Prediction ◽  
Charge Asymmetry ◽  
New Physics ◽  
Neutral Meson ◽  
Flavor Changing ◽  
The Standard Model ◽  
Meson Mixing

The recent observation of the same-sign dimuon charge asymmetry in the B system by the D0 collaboration has 3.9σ deviation from the standard model prediction. However, the recent LHCb data on Bs neutral-meson mixing do not accommodate the D0 collaboration result. In this paper, considering the effect of Z′-mediated flavor-changing neutral currents in the [Formula: see text] mixing, the same-sign dimuon charge asymmetry is calculated. We find the same-sign dimuon charge asymmetry is enhanced from its SM prediction and provides signals for new physics beyond the SM.

scholarly journals Tau lepton charge asymmetry and new physics at the LHC

2011 ◽  
Vol 84 (3) ◽  
Author(s):  
Sudhir Kumar Gupta ◽  
German Valencia
Keyword(s):  
Charge Asymmetry ◽  
New Physics ◽  
Tau Lepton ◽  
Lepton Charge

Drell-Yan Production at the Fermilab Tevatron

2005 ◽  
Vol 20 (15) ◽  
pp. 3236-3239
Author(s):  
◽  
JEDONG LEE
Keyword(s):  
Standard Model ◽  
Differential Cross Section ◽  
Invariant Mass ◽  
Cross Section ◽  
Differential Cross ◽  
Charge Asymmetry ◽  
New Physics ◽  
The Standard Model ◽  
Model Predictions ◽  
Using Data

Using data from [Formula: see text] collisions at [Formula: see text] collected by the CDF and DØ detectors, we present measurements of the Drell-Yan inclusive differential cross section and forward-backward charge asymmetry as a function of invariant mass. We compare these measurements with Standard Model predictions, and present searches for new physics that could appear as deviations from the Standard Model in the Drell-Yan differential cross section.

scholarly journals Topping-up multilepton plus b-jets anomalies at the LHC with a Z′ boson

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Ezequiel Alvarez ◽  
Aurelio Juste ◽  
Manuel Szewc ◽  
Tamara Vazquez Schroeder
Keyword(s):  
Parameter Space ◽  
Top Quark ◽  
Global Analysis ◽  
Charge Asymmetry ◽  
Top Quarks ◽  
New Physics ◽  
Initial State ◽  
Final State ◽  
The Standard Model ◽  
Physics Model

Abstract During the last years ATLAS and CMS have reported a number of slight to mild discrepancies in signatures of multileptons plus b-jets in analyses such as $$ t\overline{t}H $$ t t ¯ H , $$ t\overline{t}{W}^{\pm } $$ t t ¯ W ± , $$ t\overline{t}Z $$ t t ¯ Z and $$ t\overline{t}t\overline{t} $$ t t ¯ t t ¯ . Among them, a recent ATLAS result on $$ t\overline{t}H $$ t t ¯ H production has also reported an excess in the charge asymmetry in the same-sign dilepton channel with two or more b-tagged jets. Motivated by these tantalizing discrepancies, we study a phenomenological New Physics model consisting of a Z′ boson that couples to up-type quarks via right-handed currents: $$ {t}_R{\gamma}^{\mu }{\overline{t}}_R $$ t R γ μ t ¯ R , $$ {t}_R{\gamma}^{\mu }{\overline{c}}_R $$ t R γ μ c ¯ R , and $$ {t}_R{\gamma}^{\mu }{\overline{u}}_R $$ t R γ μ u ¯ R . The latter vertex allows to translate the charge asymmetry at the LHC initial state protons to a final state with top quarks which, decaying to a positive lepton and a b-jet, provides a crucial contribution to some of the observed discrepancies. Through an analysis at a detector level, we select the region in parameter space of our model that best reproduces the data in the aforementioned $$ t\overline{t}H $$ t t ¯ H study, and in a recent ATLAS $$ t\overline{t}t\overline{t} $$ t t ¯ t t ¯ search. We find that our model provides a better fit to the experimental data than the Standard Model for a New Physics scale of approximately ∼500 GeV, and with a hierarchical coupling of the Z′ boson that favours the top quark and the presence of FCNC currents. In order to estimate the LHC sensitivity to this signal, we design a broadband search featuring many kinematic regions with different signal-to-background ratio, and perform a global analysis. We also define signal-enhanced regions and study observables that could further distinguish signal from background. We find that the region in parameter space of our model that best fits the analysed data could be probed with a significance exceeding 3 standard deviations with just the full Run-2 dataset.

scholarly journals TOP QUARK PHYSICS AT THE LHC: A REVIEW OF THE FIRST TWO YEARS

2012 ◽  
Vol 27 (17) ◽  
pp. 1230016 ◽  
Author(s):  
FRANK-PETER SCHILLING
Keyword(s):  
Top Quark ◽  
Production Cross ◽  
Hadron Collider ◽  
Center Of Mass ◽  
Charge Asymmetry ◽  
New Physics ◽  
General Purpose ◽  
Center Of Mass Energy ◽  
Top Quark Production ◽  
Quark Production

This review summarizes the highlights in the area of top quark physics obtained with the two general purpose detectors ATLAS and CMS during the first two years of operation of the Large Hadron Collider (LHC). It covers the 2010 and 2011 data taking periods, where the LHC provided pp collisions at a center-of-mass energy of [Formula: see text]. Measurements are presented of the total and differential top quark pair production cross-section in many different channels, the top quark mass and various other properties of the top quark and its interactions, for instance the charge asymmetry. Measurements of single top quark production and various searches for new physics involving top quarks are also discussed. The already very precise experimental data are in good agreement with the standard model (SM).

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