arXiv subjects

Le Duc Ninh

Publications and source records attributed to Le Duc Ninh.

At least 19 recordsLinked to original sources

arXiv2020

Constraining new physics from Higgs measurements with Lilith-2

Lilith is a public Python library for constraining new physics from Higgs signal strength measurements. Version 2.0 of Lilith comes with an extensive XML database which includes the ATLAS and CMS Run 2 Higgs results for 36/fb, in addition the the Run 1 results. Both the code and the database were extended from the ordinary Gaussian approximation employed in Lilith-1.1 to using variable Gaussian and Poisson likelihoods. Moreover, Lilith-2 can make use of correlation matrices of arbitrary dimension. We will report on these novelties and ongoing developments. The importance of how correlations and uncertainties are treated will be demonstrated by means of detailed validations of the implemented experimental results. Moreover, we show the effects for global fits of reduced Higgs couplings, 2HDMs of Type I and Type II, and invisible Higgs decays. The program is publicly available on GitHub and can be used to constrain a wide class of new physics scenarios.

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arXiv2020

Diphoton production in vector-boson scattering at the LHC at next-to-leading order QCD

In this paper, we present results at next-to-leading order (NLO) QCD for photon pair production in association with two jets via vector boson scattering within the Standard Model (SM), and also in an effective field theory framework with anomalous gauge coupling effects via bosonic dimension-6 and 8 operators. We observe that, compared to other processes in the class of two electroweak (EW) vector boson production in association with two jets, more exclusive cuts are needed in order to suppress the SM QCD-induced background channel. As expected, the NLO QCD corrections reduce the scale uncertainties considerably. Using a well-motivated dynamical scale choice, we find moderate $K$-factors for the EW-induced process while the QCD-induced channel receives much larger corrections. Furthermore, we observe that applying a cut of $Δϕ_{j_2 γ_1}^{\text{cut}} < 2.5$ for the second hardest jet and the hardest photon helps to increase the signal significance and reduces the impact of higher-order QCD corrections.

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arXiv2020

Polarization observables in WZ production at the 13 TeV LHC: Inclusive case

We present a study of the polarization observables of the $W$ and $Z$ bosons in the process $p p \to W^\pm Z\to e^\pm ν_e μ^+μ^-$ at the 13 TeV Large Hadron Collider. The calculation is performed at next-to-leading order, including the full QCD corrections as well as the electroweak corrections, the latter being calculated in the double-pole approximation. The results are presented in the helicity coordinate system adopted by ATLAS and for different inclusive cuts on the di-muon invariant mass. We define left-right charge asymmetries related to the polarization fractions between the $W^+ Z$ and $W^- Z$ channels and we find that these asymmetries are large and sensitive to higher-order effects. Similar findings are also presented for charge asymmetries related to a P-even angular coefficient.

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arXiv2020

VBSCan Mid-Term Scientific Meeting

This document summarises the talks and discussions happened during the VBSCan Mid-Term Scientific Meeting workshop. The VBSCan COST action is dedicated to the coordinated study of vector boson scattering (VBS) from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.

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arXiv2019

Constraining new physics from Higgs measurements with Lilith: update to LHC Run 2 results

Lilith is a public Python library for constraining new physics from Higgs signal strength measurements. We here present version 2.0 of Lilith together with an updated XML database which includes the current ATLAS and CMS Run 2 Higgs results for 36/fb. Both the code and the database were extended from the ordinary Gaussian approximation employed in Lilith-1.1 to using variable Gaussian and Poisson likelihoods. Moreover, Lilith can now make use of correlation matrices of arbitrary dimension. We provide detailed validations of the implemented experimental results as well as a status of global fits for reduced Higgs couplings, Two-Higgs-doublet models of Type I and Type II, and invisible Higgs decays. Lilith-2.0 is available on GitHub and ready to be used to constrain a wide class of new physics scenarios.

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arXiv2019

Next-to-leading order QCD corrections for single top-quark production in association with two jets

In this article we calculate the next-to-leading order (NLO) QCD corrections for single on-shell top-quark production in association with two jets at proton-proton colliders. The tW channel is assumed to be measured independently. The QCD corrections to the inclusive cross section are about 28 (22)\% for top (anti-top) quark production at the 13 TeV LHC. Theoretical errors are dominated by scale uncertainties, which are found to be around 5\% at NLO. Results for various kinematical distributions are also provided using a well-motivated dynamical scale. The QCD corrections are found to have a non-trivial dependence on the phase-space.

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arXiv2019

Polarisation at NLO in WZ production at the LHC

The pair production of a $W$ and a $Z$ boson at the LHC is an important process to study the triple-gauge boson couplings as well as to probe new physics that could arise in the gauge sector. In particular the leptonic channel $p p \to W^\pm Z\to 3\ell +ν+ X$ is considered by ATLAS and CMS collaborations. Polarisation observables can help pinning down new physics and give information on the spin of the gauge bosons. Measuring them requires high statistics as well as precise theoretical predictions. We define in this contribution fiducial polarisation observables for the $W$ and $Z$ bosons and we present theoretical predictions in the Standard Model at next-to-leading order (NLO) including QCD as well as NLO electroweak corrections, the latter in the double-pole approximation. We also show that this approximation works remarkably well for $W^\pm Z$ production at the LHC by comparing to the full results.

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arXiv2018

On the triplet anti-triplet symmetry in 3-3-1 models

We present a detailed discussion of the triplet anti-triplet symmetry in 3-3-1 models. The full set of conditions to realize this symmetry is provided, which includes in particular the requirement that the two vacuum expectation values of the two scalar triplets responsible for making the W and Z bosons massive must be interchanged. We apply this new understanding to the calculation of processes that have a Z-Z' mixing.

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arXiv2018

WZ production at the LHC: Polarization observables in the Standard Model

WZ production is an important process at the LHC because it probes the non-Abelian structureof electroweak interactions and it is a background process for many new physics searches. In the quest for new physics, polarization observables of the W and Z bosons can play an important role. They can be extracted from measurements and can be calculated using the Standard Model. In this contribution, we define fiducial polarization observables of the W and Z bosons and discuss the effects of next-to-leading order electroweak and QCD corrections in the Standard Model.

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arXiv2016

A theoretical status of weak gauge boson pair production at the LHC

Weak gauge boson pair production is an important process at the LHC because it probes the non-Abelian structure of electroweak interactions and it is a background process for many new physics searches, and with enough statistics we can perform comparisons between measurements and theoretical calculations for different but correlated observables. In these proceedings, we present a theoretical status including state-of-the-art results from recent calculations of higher-order QCD and electroweak corrections.

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arXiv2016

Massive gauge boson pair production at the LHC: a next-to-leading order story

Electroweak gauge boson pair production is one of the most important Standard Model processes at the LHC, not only because it is a benchmark process but also by its ability to probe the electroweak interaction directly. We present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model. This includes the QCD and electroweak (EW) corrections. We study the hierarchy between the different channels when looking at the size of the QCD gluon-induced processes and the EW photon-induced processes and provide the first comprehensive explanation of this hierarchy thanks to analytical leading-logarithmic results. We also provide a detailed study of the theoretical uncertainties affecting the total cross section predictions that stem from scale variation, parton distribution function and $α_s$ errors. We then compare with the present LHC data.

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arXiv2016

The simplest 3-3-1 model

A simple extension of the Standard Model (SM), based on the gauge group $SU(3)_C\otimes SU(3)_L\otimes U(1)_Y$ with $Y$ being the hypercharge, is considered. We show that, by imposing an approximate global $SU(2)_L\times SU(2)_R$ custodial symmetry at the SM energy scale, the $Z-Z'$ mixing is absent at tree level and the value of the $ρ$ parameter can be kept close to one. Tree-level flavor-changing neutral currents are also reduced to three particles, namely $Z'$, a CP-odd Higgs and a CP-even Higgs. The model predicts new leptons with electric charges of $\pm 1/2e$ and new quarks with $\pm 1/6e$ charges as well as new gauge and scalar bosons with $\pm 1/2e$ charges. Electric charge conservation requires that one of them must be stable. Their masses are unfortunately free parameters.

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arXiv2014

QCD Induced Di-boson Production in Association with Two Jets at NLO QCD

We discuss results for di-boson plus two jets production processes at the LHC at NLO QCD. Issues related to the scale choice are reviewed. We focus on the distributions of the invariant mass and rapidity separation of the two hardest jets and show, for $W^\pm γjj$ and $Zγjj$ production, how the contribution from the radiative decays of the massive gauge bosons can be significantly reduced.

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arXiv2014

$Zγ$ production in association with two jets at next-to-leading order QCD

Next-to-leading order QCD corrections to the QCD-induced $pp \rightarrow l^+l^- γj j +X$ and $pp \rightarrow \barν_l ν_l γjj+X$ processes are presented. The latter is used to find an optimal cut to reduce the contribution of radiative photon emission off the charged leptons in the first channel. As expected, the scale uncertainties are significantly reduced at NLO and the QCD corrections are phase space dependent and important for precise measurements at the LHC.

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arXiv2014

Next-to-leading order QCD corrections to ZZ production in association with two jets

We present the first calculation of next-to-leading order QCD corrections to QCD-induced ZZ production in association with two jets at hadron colliders. Both Z bosons decay leptonically with all off-shell effects, virtual photon contributions and spin-correlation effects fully taken into account. This process is an important background to weak boson scattering, to the measurement of quartic gauge couplings and to searches for signals of new physics beyond the Standard Model. As expected, the next-to-leading order corrections reduce significantly the scale uncertainty and show a non-trivial phase space dependence in kinematic distributions. Our code will be publicly available as part of the parton level Monte Carlo program VBFNLO.

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arXiv2014

Next-to-leading order QCD corrections to $W^+W^+$ and $W^-W^-$ production in association with two jets

We present a study of $W^+W^+jj$ and $W^-W^-jj$ production including leptonic decays in hadron-hadron collisions. The full electroweak and QCD induced contributions and their interferences are calculated at leading order. We find that, for inclusive cuts, the interference effects can be large if the jets are produced with large transverse momentum where, however, the production rate is suppressed. We also discuss the vector-boson-fusion (VBF) cuts and show the validity of the VBF approximation. The NLO QCD corrections to the QCD-induced channels are also calculated. Compared to the previous calculation, we allow the intermediate $W$ bosons to be off-shell. For on-shell $W$ production, we obtain an excellent agreement with previous results. Our code will be publicly available as part of the parton level Monte Carlo program VBFNLO.

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arXiv2014

Next-to-leading order QCD corrections to $W γ$ production in association with two jets

The QCD-induced $W^\pm γ$ production channels in association with two jets are computed at next-to-leading order QCD accuracy. The W bosons decay leptonicly and full off-shell and finite width effects as well as spin correlations are taken into account. These processes are important backgrounds to beyond Standard Model physics searches and also relevant to test the nature of the quartic gauge couplings of the Standard Model. The next-to-leading order corrections reduce the scale uncertainty significantly and show a non-trivial phase space dependence. Our code will be publicly available as part of the parton level Monte Carlo program VBFNLO.

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arXiv2013

NLO WWZ production at the LHC

The tri-boson production is one of the key processes for the study of quartic gauge couplings. Next-to-leading order (NLO) corrections are mandatory to reduce theoretical uncertainties. In this study, the most up-to-date predictions including NLO QCD and NLO EW corrections to the total cross section and distributions of the WWZ production at the LHC are presented. We show that the QCD correction is about 100% and the EW correction is of a few percent at the total cross section level. The EW correction however becomes significant in the high energy regime of the gauge boson transverse momentum distributions.

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