Electroweak Gauge Boson Production Research Articles

Locally finite two-loop amplitudes for electroweak production through gluon fusion

The computation of two-loop amplitudes for the production of multiple Higgs and electroweak gauge bosons via gluon fusion with exact dependence on quark masses relies primarily on numerical methods. We propose a framework that enables their numerical evaluation in momentum space. The method is inspired by the factorization of infrared divergences in QCD scattering amplitudes. It extends techniques introduced for electroweak gauge boson production from quark-antiquark annihilation to processes with external gluons. By combining diagrammatic integrands, we make use of local cancellations between diagrams that automatically eliminate most non-factoring infrared singularities. With a limited number of counterterms, we then derive two-loop integrands for which all soft and collinear singularities factorize locally. We hope that the local subtraction techniques presented in this article will play a useful role in extending the local factorization formalism to two-loop amplitudes for arbitrary processes.

Production of electroweak gauge bosons at forward rapidities in the color-dipole S-matrix framework

The cross-section for the production of an electroweak gauge boson (G = W±, Z0, γ) at forward rapidities in pp collisions is derived within the color-dipole S-matrix framework. We present the full expressions for the differential cross-section of the qp → GX process in the impact parameter and transverse momentum spaces, considering the longitudinal and transverse polarizations of the gauge boson. The particular cases associated with the Drell-Yan process and real photon production are discussed. We demonstrate that the final formulae are expressed in terms of the dipole-proton cross-section or the unintegrated gluon distribution, and can be used to estimate the impact of the saturation effects in the gauge boson production at the LHC and future colliders.

The PDF4LHC21 combination of global PDF fits for the LHC Run III* *We dedicate this paper to the memory of James Stirling, Dick Roberts and Jon Pumplin, all of whom sadly died in the past few years. All three were instrumental in the development and evolution of PDF fitting, Jon for the CTEQ-TEA collaboration and James and Dick for the

A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton–hadron and hadron–hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin of the differences between the three global PDF sets. In particular, dedicated fits based on almost identical theory settings and input datasets are performed by the three groups, highlighting the role played by the respective fitting methodologies. We compare the new PDF4LHC21 combination with its predecessor, PDF4LHC15, demonstrating their good overall consistency and a modest reduction of PDF uncertainties for key LHC processes such as electroweak gauge boson production and Higgs boson production in gluon fusion. We study the phenomenological implications of PDF4LHC21 for a representative selection of inclusive, fiducial, and differential cross sections at the LHC. The PDF4LHC21 combination is made available via the LHAPDF library and provides a robust, user-friendly, and efficient method to estimate the PDF uncertainties associated to theoretical calculations for the upcoming Run III of the LHC and beyond.

NNNPDF3.0: evidence for a modified partonic structure in heavy nuclei

We present an updated determination of nuclear parton distributions (nPDFs) from a global NLO QCD analysis of hard processes in fixed-target lepton-nucleus and proton-nucleus together with collider proton-nucleus experiments. In addition to neutral- and charged-current deep-inelastic and Drell–Yan measurements on nuclear targets, we consider the information provided by the production of electroweak gauge bosons, isolated photons, jet pairs, and charmed mesons in proton-lead collisions at the LHC across centre-of-mass energies of 5.02 TeV (Run I) and 8.16 TeV (Run II). For the first time in a global nPDF analysis, the constraints from these various processes are accounted for both in the nuclear PDFs and in the free-proton PDF baseline. The extensive dataset underlying the nNNPDF3.0 determination, combined with its model-independent parametrisation, reveals strong evidence for nuclear-induced modifications of the partonic structure of heavy nuclei, specifically for the small-x shadowing of gluons and sea quarks, as well as the large-x anti-shadowing of gluons. As a representative phenomenological application, we provide predictions for ultra-high-energy neutrino-nucleon cross-sections, relevant for data interpretation at neutrino observatories. Our results provide key input for ongoing and future experimental programs, from that of heavy-ion collisions in controlled collider environments to the study of high-energy astrophysical processes.

Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms

In implementations of the electroweak scale cosmological relaxation mechanism proposed so far, the effect of the quantum fluctuations of the homogeneous relaxion field has been ignored. We show that they can grow during the classical cosmological evolution of the relaxion field passing through its many potential barriers. The resulting production of relaxion particles can act as an efficient stopping mechanism for the relaxion. We revisit the original relaxion proposal and determine under which conditions inflation may no longer be needed as a source of friction. We review alternative stopping mechanisms and determine in detail the allowed parameter space for each of them (whether happening before, during and after inflation), also considering and severely constraining the case of friction from electroweak gauge boson production in models with large and Higgs-independent barriers.

Electroweak boson production at large transverse momentum in double polarized pp scattering at next-to-leading order accuracy

We compute the next-to-leading order corrections to the cross section for the production of electroweak gauge bosons ($Z$, $W^\pm$ and $\gamma^*$) with large transverse momentum in double (longitudinally) polarized hadronic collisions. The calculation is fully performed in the HVBM scheme within dimensional regularization with a careful treatment of issues arising due to the appearance of $\gamma^5$ in polarization projectors and axial couplings. We study the phenomenological consequences of the NLO corrections at the level of both the double polarized cross section and the corresponding asymmetries at RHIC kinematics.

Relation between the parton branching approach and Catani-Ciafaloni-Fiorani-Marchesini evolution

We consider the associated production of electroweak gauge bosons and charm or beauty quark jets at the LHC using the $k_T$-factorization framework. We apply the transverse momentum dependent (TMD) parton distributions in a proton obtained from the Parton Branching (PB) method as well as from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. For the PB approach, our prescription merges the standard leading order ${\cal O}(\alpha \alpha_s)$ $k_T$-factorization calculations with several tree-level next-to-leading order ${\cal O}(\alpha \alpha_s^2)$ off-shell production amplitudes. For the CCFM scenario, our consideration is based on the ${\cal O}(\alpha \alpha_s^2)$ off-shell gluon-gluon fusion subprocess $g^* g^* \to Z/W + Q\bar Q$ and some subleading ${\cal O}(\alpha \alpha_s^2)$ subprocesses involving quark interactions, taken into account in conventional (collinear) QCD factorization. We find that the $W + c$ and $Z + b$ cross sections, calculated within the PB and CCFM-based schemes with the proper choice of leading and next-to-leading subprocesses, are in good agreement with each other, thus establishing a correspondence between these two scenarios. A comparison with the latest LHC experimental data is given and the necessity for the proper off-shell treatment of the production amplitudes in determination of the parameters of the TMD parton density is demonstrated.

Neutral triple vector boson production in Randall-Sundrum model at the LHC

In this paper, triple neutral electroweak gauge boson production processes, viz. \gamma\gamma\gamma, \gamma\gamma Z, \gamma ZZ and ZZZ productions merged to 1-jet have been studied at the leading order in QCD in the context of Randall-Sundrum model at the LHC with center of mass energy \sqrt{S}=13 TeV. Decay of Z bosons into lepton-pairs has been considered. We present a selection of kinematical distributions matched to parton shower and show their deviation from the SM results as a result of the RS model. The uncertainties as a result of the factorization and renormalization scales are also presented.

Electroweak gauge-boson production in association with b jets at Hadron Colliders

The production of both charged and neutral electroweak gauge bosons in association with b jets has attracted a lot of experimental and theoretical attention in recent years because of its central role in the physics programs of both the Fermilab Tevatron and the CERN Large Hadron Collider. The improved level of accuracy achieved both in the theoretical predictions and experimental measurements of these processes can promote crucial developments in modeling b-quark jets and b-quark parton distribution functions, and can provide a more accurate description of some of the most important backgrounds to the measurement of Higgs-boson couplings and several new physics searches. In this paper, we review the status of theoretical predictions for cross sections and kinematic distributions of processes in which an electroweak gauge boson is produced in association with up to two b jets in hadronic collisions, namely [Formula: see text], pp → V + 1b jet and [Formula: see text], pp → V + 2b jets with V = W±, Z/γ*, γ. Available experimental measurements at both the Fermilab Tevatron and the CERN Large Hadron Collider are also reviewed and their comparison with theoretical predictions is discussed.

Hadron structure beyond collinear level and precision DIS measurements

General formulations of QCD factorization for hadronic collisions extend the notion of ordinary parton distributions to transverse-momentum dependent (TMD) parton density and parton decay functions. We discuss the use of the recent high-precision deep-inelastic scattering (DIS) measurements for determination of TMD distributions. These are relevant for both low-pT and high-pT physics in hadron collisions. We comment on applications to multi-jet final states associated with electroweak gauge boson production at the LHC.

Higgs-boson production at small transverse momentum

Using methods from effective field theory, we have recently developed a novel, systematic framework for the calculation of the cross sections for electroweak gauge-boson production at small and very small transverse momentum q_T, in which large logarithms of the scale ratio m_V/q_T are resummed to all orders. This formalism is applied to the production of Higgs bosons in gluon fusion at the LHC. The production cross section receives logarithmically enhanced corrections from two sources: the running of the hard matching coefficient and the collinear factorization anomaly. The anomaly leads to the dynamical generation of a non-perturbative scale q_* ~ m_H e^{-const/\alpha_s(m_H)} ~ 8 GeV, which protects the process from receiving large long-distance hadronic contributions. We present detailed numerical predictions for the transverse-momentum spectrum of the Higgs boson, finding that it is quite insensitive to hadronic effects.

Neutral triple electroweak gauge boson production in the large extra-dimension model at the LHC

We study the prospects of probing large extra-dimension models at the LHC through neutral triple gauge boson production processes. In theories with extra dimensions these processes result from the exchange of a tower of massive graviton modes between the SM particles. We consider $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\gamma}$, $\ensuremath{\gamma}\ensuremath{\gamma}Z$, $\ensuremath{\gamma}ZZ$, and $ZZZ$ production processes, and present our results for various kinematic distributions at the LHC for $\sqrt{S}=14\text{ }\text{ }\mathrm{TeV}$.

Electroweak gauge-boson production at small q T : Infrared safety from the collinear anomaly

Using methods from effective field theory, we develop a novel, systematic framework for the calculation of the cross sections for electroweak gauge-boson production at small and very small transverse momentum q_T, in which large logarithms of the scale ratio M_V/q_T are resummed to all orders. These cross sections receive logarithmically enhanced corrections from two sources: the running of the hard matching coefficient and the collinear factorization anomaly. The anomaly leads to the dynamical generation of a non-perturbative scale q_* ~ M_V e^{-const/\alpha_s(M_V)}, which protects the processes from receiving large long-distance hadronic contributions. Expanding the cross sections in either \alpha_s or q_T generates strongly divergent series, which must be resummed. As a by-product, we obtain an explicit non-perturbative expression for the intercept of the cross sections at q_T=0, including the normalization and first-order \alpha_s(q_*) correction. We perform a detailed numerical comparison of our predictions with the available data on the transverse-momentum distribution in Z-boson production at the Tevatron and LHC.

SUSY QCD corrections to electroweak gauge boson production with an associated jet at the LHC

We study the stability of the neutral- and charged-current Drell-Yan process in association with a jet as a standard candle at the LHC under the inclusion of O(alpha_s) supersymmetric QCD (SQCD) corrections within the MSSM. We include the decay of the electroweak gauge boson into dileptons, i.e. we consider the production of charged lepton--anti-lepton or lepton-neutrino final states with one hard jet. We find that the SQCD corrections are negligible for the integrated cross section. Only at high lepton transverse momentum can they induce effects of the percent level.

On the quark component in prompt photon and electroweak gauge boson production at high energies

In the framework of the kT-factorization approach, we study the production of prompt photons and electroweak gauge bosons in high-energy proton–(anti)proton collisions at modern colliders. Our consideration is based on the amplitude for the production of a single photon or W±/Z0 boson associated with a quark pair in the fusion of two off-shell gluons. The quark component is taken into account separately using the quark–gluon scattering and quark–antiquark annihilation QCD subprocesses. Special attention is given to the contributions from the quarks involved in the earlier steps of the evolution cascade. Using the Kimber–Martin–Ryskin formalism, we simulate this component and demonstrate that it plays an important role at both the Tevatron and LHC energies. Our theoretical results are compared with recent experimental data taken by the D∅ and CDF Collaborations at the Tevatron.

Production of electroweak gauge bosons in off-shell gluon-gluon fusion

We study the production of electroweak gauge bosons at high energies in the framework of k{sub T}-factorization QCD approach. The amplitude for production of a single W{sup {+-}} or Z{sup 0} boson associated with quark pair in the fusion of two off-shell gluons is calculated. Contributions from the valence quarks are calculated using the quark-gluon interaction and quark-antiquark annihilation QCD subprocesses. The total and differential cross sections (as a function of the transverse momentum and rapidity) are presented and the ratio of cross sections for W{sup {+-}} and Z{sup 0} boson production is investigated. The conservative error analysis is performed. In the numerical calculations two different sets of unintegrated gluon distributions in the proton are used: the one obtained from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation and the other from the Kimber-Martin-Ryskin prescription. Theoretical results are compared with experimental data taken by the D0 and CDF collaborations at the Tevatron. We demonstrate the importance of the quark component in parton evolution in description of the experimental data. This component is very significant also at the LHC energies.

Review of precision calculations for the measurement of electroweak boson production and properties at hadron colliders

We review the present status of precision calculations and tools for the study of single electroweak gauge boson production at hadron colliders. The state-of-the-art of higher-order electroweak and QCD calculations, as well as their combination, is summarized, paying particular attention to the precision measurements of the W-boson parameters at the Fermilab Tevatron and CERN LHC.

Pp→jje±μ±ννandjje±μ∓ννatO(αem6)andO(αem4αs2)for the study of the quartic electroweak gauge boson vertex at CERN LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study the structure of quartic vector-boson interactions through the pair production of electroweak gauge bosons via weak boson fusion $qq\ensuremath{\rightarrow}qqWW$. In order to study these couplings we have performed a partonic level calculation of all processes $pp\ensuremath{\rightarrow}jj{e}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}\ensuremath{\nu}$ and $pp\ensuremath{\rightarrow}jj{e}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ensuremath{\mp}}\ensuremath{\nu}\ensuremath{\nu}$ at the LHC using the exact matrix elements at $\mathcal{O}({\ensuremath{\alpha}}_{\mathrm{em}}^{6})$ and $\mathcal{O}({\ensuremath{\alpha}}_{\mathrm{em}}^{4}{\ensuremath{\alpha}}_{s}^{2})$ as well as a full simulation of the $t\overline{t}$ plus 0 to 2 jets backgrounds. A complete calculation of the scattering amplitudes is necessary not only for a correct description of the process but also to preserve all correlations between the final-state particles which can be used to enhance the signal. Our analyses indicate that the LHC can improve by more than 1 order of magnitude the bounds arising at the present from indirect measurements.

Probing trilinear gauge boson interactions via single electroweak gauge boson production at the CERN LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous trilinear vector-boson interactions W{sup +}W{sup -}{gamma} and W{sup +}W{sup -}Z through the single production of electroweak gauge bosons via the weak boson fusion processes qq{yields}qqW({yields}l{sup {+-}}{nu}) and qq{yields}qqZ({yields}l{sup +}l{sup -}) with l=e or {mu}. After a careful study of the standard model backgrounds, we show that the single production of electroweak bosons at the LHC can provide stringent tests on deviations of these vertices from the standard model prediction. In particular, we show that single gauge-boson production exhibits a sensitivity to the couplings {delta}{kappa}{sub Z,{gamma}} similar to that attainable from the analysis of electroweak boson pair production.