$$tZ'$$ production at hadron colliders

Guzzi, Marco; Kidonakis, Nikolaos

doi:10.1140/epjc/s10052-020-8028-1

“…In addition to tZ production discussed in the previous subsection, top quarks can also be produced in association with Z ′ or W ′ bosons [151] (see Ref. [152] for models of such particles).…”

Section: Other Top-quark Production Processes Via Anomalous Couplingsmentioning

confidence: 99%

Soft-gluon corrections in top-quark production

Kidonakis

¹

2018

Int. J. Mod. Phys. A

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I review calculations of soft-gluon corrections for top-quark production in hadron collisions. I describe theoretical formalisms for their resummation and for finite-order expansions. I show that soft-gluon corrections are dominant for a large number of top-quark processes. I discuss top-antitop pair production as well as single-top production, including total cross sections and differential distributions, and compare with data from the LHC and the Tevatron. I also discuss top-quark production in association with charged Higgs bosons, Z bosons, and other particles in models of new physics.In Section 5, I discuss single-top production, including t-channel and s-channel production, and tW production, and I present total cross sections and top-quark p T and rapidity distributions. In Section 6, I discuss top-quark production in association with a charged Higgs boson, and in association with gauge bosons via anomalous couplings in new-physics models. I conclude with a summary in Section 7. Soft-gluon correctionsSoft-gluon corrections arise from the emission of low-energy gluons, and they result from incomplete cancellations of infrared divergences between virtual diagrams and diagrams with real emission.These corrections appear in the perturbative series as plus distributions involving logarithms of a variable that measures the kinematical distance from threshold. For the nth-order perturbative corrections, the leading logarithms are those with the highest power, 2n − 1; the next-to-leading logarithms have a power of 2n − 2; etc. The effects of soft-gluon corrections are particularly relevant near partonic threshold. At partonic threshold there is no energy for additional radiation, but the top quark may have non-zero momentum and is not restricted to be produced at rest. Thus, partonic threshold is a more general concept than production or absolute threshold, where the top quark is produced at rest.For top-antitop production, several threshold variables have been used for resummation. In single-particle-inclusive (1PI) kinematics, the partonic threshold variable is s 4 = s+t+u− m 2 where s, t, and u are the standard kinematical variables and the sum is over the masses squared of all particles in the scattering. At partonic threshold, s 4 → 0. In pair-invariant-mass (PIM) kinematics, the partonic threshold variable is 1 −z = 1 −M 2 tt /s, where M tt is the invariant mass of the top-antitop pair; at partonic threshold z → 1. In resummation using absolute threshold -a special limiting case of partonic threshold as we discussed above -the threshold variable is β = 1 − 4m 2 t /s, where m t is the top-quark mass; at absolute threshold, β → 0. Formalisms that use partonic threshold in 1PI or PIM kinematics involve a general resummation for double-differential distributions, from which single distributions or total cross sections can be derived by appropriate integrations. Formalisms that use absolute threshold are limited only to total cross sections.Similarly, 1PI kinematics have been used in resummations for single-top p...

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“…We also incorporate specific trigger selection efficiencies for each leptonic channel to the ROOT [45] code used to analyse the Delphes output. The simulated signal samples have been normalized using k-factors obtained from simulating similar events to NLO with the same set-up, and which are consistent with those in the literature [46].…”

Section: Jhep05(2021)125mentioning

confidence: 93%

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

Álvarez

¹

,

Juste

²

,

Szewc

³

et al. 2021

J. High Energ. Phys.

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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.

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“…Models for W /Z s in Drell-Yan resonant dilepton production are currently being scrutinized at the LHC [46,47]. At high energies, W /Z s can also be produced in association with another SM vector or scalar boson, or in association with a jet or single heavy quark [48,49]. Current LHC bounds on mass disfavor extra vector bosons lighter than approximately 4-5 TeV.…”

Section: Pdfs and Bsm Searchesmentioning

confidence: 99%

Snowmass 2021 whitepaper: Proton structure at the precision frontier

Amoroso,

Apyan,

Armesto

et al. 2022

Preprint

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An overwhelming number of theoretical predictions for hadron colliders require parton distribution functions (PDFs), which are an important ingredient of theory infrastructure for the next generation of high-energy experiments. This whitepaper summarizes the status and future prospects for determination of high-precision PDFs applicable in a wide range of energies and experiments, in particular in precision tests of the Standard Model and in new physics searches at the high-luminosity Large Hadron Collider and Electron-Ion Collider. We discuss the envisioned advancements in experimental measurements, QCD theory, global analysis methodology, and computing that are necessary to bring unpolarized PDFs in the nucleon to the N2LO and N3LO accuracy in the QCD coupling strength. Special attention is given to the new tasks that emerge in the era of the precision PDF analysis, such as those focusing on the robust control of systematic factors both in experimental measurements and theoretical computations. Various synergies between experimental and theoretical studies of the hadron structure are explored, including opportunities for studying PDFs for nuclear and meson targets, PDFs with electroweak contributions or dependence on the transverse momentum, for incisive comparisons between phenomenological models for the PDFs and computations on discrete lattice, and for cross-fertilization with machine learning/AI approaches.

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$$tZ'$$ production at hadron colliders

Cited by 11 publications

References 58 publications

Soft-gluon corrections in top-quark production

Soft-gluon corrections in top-quark production

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

Snowmass 2021 whitepaper: Proton structure at the precision frontier

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