W-boson Pair Production Research Articles

Polarized electroweak bosons in W+W\u2212 production at the LHC including NLO QCD effects

The measurement of polarization fractions of massive gauge bosons at the LHC provides an important check of the Standard Model and in particular of the Electroweak Symmetry Breaking mechanism. Owing to the unstable character of W and Z bosons, devising a theoretical definition for polarized signals is not straightforward and always subject to some ambiguity. Focusing on W-boson pair production at the LHC in the fully leptonic channel, we propose to compute polarized cross-sections and distributions based on the gauge-invariant doubly-resonant part of the amplitude. We include NLO QCD corrections to the leading quark-induced partonic process and also consider the loop- induced gluon-initiated process contributing to the same final state. We present results for both an inclusive setup and a realistic fiducial region, with special focus on variables that are suited for the discrimination of polarized cross-sections and on quantities that can be measured experimentally.

Next-to-leading-order electroweak corrections to pp → W+W− → 4 leptons at the LHC

We present results of the first calculation of next-to-leading-order electroweak corrections to W-boson pair production at the LHC that fully takes into account leptonic W-boson decays and off-shell effects. Employing realistic event selections, we discuss the corrections in situations that are typical for the study of W-boson pairs as a signal process or of Higgs-boson decays $H\to W W^*$, to which W-boson pair production represents an irreducible background. In particular, we compare the full off-shell results, obtained treating the W-boson resonances in the complex-mass scheme, to previous results in the so-called double-pole approximation, which is based on an expansion of the loop amplitudes about the W resonance poles. At small and intermediate scales, i.e. in particular in angular and rapidity distributions, the two approaches show the expected agreement at the level of fractions of a percent, but larger differences appear in the TeV range. For transverse-momentum distributions, the differences can even exceed the 10% level in the TeV range where "background diagrams" with one instead of two resonant W bosons gain in importance because of recoil effects.

Study of vector boson scattering and search for new physics in events with two same-sign leptons and two jets.

A study of vector boson scattering in pp collisions at a center-of-mass energy of 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.4 fb(-1) collected with the CMS detector. Candidate events are selected with exactly two leptons of the same charge, two jets with large rapidity separation and high dijet mass, and moderate missing transverse energy. The signal region is expected to be dominated by electroweak same-sign W-boson pair production. The observation agrees with the standard model prediction. The observed significance is 2.0 standard deviations, where a significance of 3.1 standard deviations is expected based on the standard model. Cross section measurements for W(±)W(±) and WZ processes in the fiducial region are reported. Bounds on the structure of quartic vector-boson interactions are given in the framework of dimension-eight effective field theory operators, as well as limits on the production of doubly charged Higgs bosons.

Double-parton scattering cross sections in proton–nucleus and nucleus–nucleus collisions at the LHC

Simple generic expressions to compute double-parton scattering (DPS) cross sections in high-energy proton-nucleus and nucleus-nucleus collisions, as a function of the corresponding single-parton cross sections, are presented. Estimates of DPS contributions are studied for two specific processes at LHC energies: (i) same-sign W-boson pair production in p-Pb, and (ii) double-J/psi production in Pb-Pb, using NLO predictions with nuclear parton densities for the corresponding single-parton cross sections. The expected DPS cross sections and event rates after typical acceptance and efficiency losses are also given for other processes involving J/psi and W,Z gauge bosons in p-Pb and Pb-Pb collisions at the LHC.

Aspects des complications ostéoarticulaires de la maladie de Gaucher de type 1 en scintigraphie osseuse planaire (infection exclue) : à propos d’un cas

Simple generic expressions to compute double-parton scattering (DPS) cross sections in high-energy proton–nucleus and nucleus–nucleus collisions, as a function of the corresponding single-parton cross sections, are presented. Estimates of DPS contributions are studied for two specific processes at LHC energies: (i) same-sign W-boson pair production in p–Pb, and (ii) double-J/ψ production in Pb–Pb, using NLO predictions with nuclear parton densities for the corresponding single-parton cross sections. The expected DPS cross sections and event rates after typical acceptance and efficiency losses are also given for other processes involving J/ψ and W, Z gauge bosons in p–Pb and Pb–Pb collisions at the LHC.

Next-to-leading order electroweak corrections to pp → W+W− → 4 leptons at the LHC in double-pole approximation

We present the calculation of next-to-leading-order electroweak corrections to W-boson pair production at the LHC, taking off-shell effects of the W bosons and their leptonic decays into account in the framework of the so-called double-pole approximation. In detail, the lowest-order cross section and the photonic bremsstrahlung are based on full matrix elements with four-fermion final states, but the virtual one-loop corrections are approximated by the leading contributions of a systematic expansion about the resonance poles of the two W bosons. This expansion classifies the virtual corrections into factorizable and non-factorizable corrections, the calculation of which is described in detail. Corrections induced by photons in the initial state, i.e. photon-photon and quark-photon collision channels, are included and based on complete matrix elements as well. Our numerical results, which are presented for realistic acceptance cuts applied to the W-boson decay products, qualitatively confirm recent results obtained for on-shell W bosons and reveal electroweak corrections of the size of tens of percent in the TeV range of transverse momenta and invariant masses. In general, photon-photon and quark-photon induced contributions amount to 5-10% of the full differential result. Compared to previous predictions based on stable W bosons electroweak corrections, however, can change by several percent because of realistic cuts on the W-boson decay products and corrections to the decays.

Electroweak corrections to W-boson pair production at the LHC

Vector-boson pair production ranks among the most important Standard-Model benchmark processes at the LHC, not only in view of on-going Higgs analyses. These processes may also help to gain a deeper understanding of the electroweak interaction in general, and to test the validity of the Standard Model at highest energies. In this work, the first calculation of the full one-loop electroweak corrections to on-shell W-boson pair production at hadron colliders is presented. We discuss the impact of the corrections on the total cross section as well as on relevant differential distributions. We observe that corrections due to photon-induced channels can be amazingly large at energies accessible at the LHC, while radiation of additional massive vector bosons does not influence the results significantly.

The process [formula omitted] as a probe into the EWSB mechanism

We discuss the excellent prospects of the gluon–gluon fusion process gg→4f for the study of the electroweak symmetry breaking mechanism (EWSB) at the LHC. This channel includes the longitudinal W-boson pair production through the subprocess tt¯→W+W−. The shape and magnitude of cross sections and distributions thus provide a powerful tool for determining the nature of a possible strongly interacting electroweak sector. In our analysis, we consider the exact matrix element at O(αsαem2), and we include all irreducible background coming from qq¯→4f. Purely leptonic final states, pp→lν¯lνl′l¯′, are numerically investigated by comparing the Standard Model with the no-Higgs scenario. We find that this channel is extremely sensitive to the regime of the interaction between gauge bosons. It can thus be associated to the traditionally used vector boson scattering (VBS) to improve the analysis of the EWSB physics at the LHC.

Measurement of the cross section of W-boson pair production at LEP

The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4 pb−1, collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4% and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W→hadrons)=67.50±0.42(stat.)±0.30(syst.)%, in agreement with the Standard Model. Differential cross sections as a function of the W− production angle are also measured for the semi-leptonic channels qqeν and qqμν.

Measurement of the cross section of W-boson pair production at LEP

The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4 pb−1, collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4% and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W→hadrons)=67.50±0.42(stat.)±0.30(syst.)%, in agreement with the Standard Model. Differential cross sections as a function of the W− production angle are also measured for the semi-leptonic channels qqeν and qqμν.

Measurement of W-pair cross sections in e +e − interactions at [formula omitted] and W-decay branching fractions

We report on the measurement of W-boson pair-production with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 55.47 pb −1 collected at an average centre-of-mass energy of 182.68 GeV , we select 824 four-fermion events with pairs of hadronic jets or pairs of leptons with high invariant masses. Branching fractions of W decays into different fermion-antifermion pairs are determined. Assuming charged-current lepton universality, the branching fraction for hadronic W decays is measured to be: B( W→hadrons)=70.1±1.3 (stat.)±0.4 (syst.) % . Combining all final states the total cross section for W-pair production is measured to be: σ WW =16.53±0.67 (stat.)±0.26 (syst.) pb.

Measurement of W-pair cross sections in e+e− interactions at =172 and W-decay branching fractions

Abstract We report on the measurement of W-boson pair-production with the L3 detector at LEP at an average centre-of-mass energy of 172.13 GeV. In a data sample corresponding to a total luminosity of 10.25 pb−1 we select 110 four-fermion events with pairs of hadronic jets or leptons with high invariant masses. Branching fractions of W decays into different fermion-antifermion pairs are determined with and without the assumption of charged-current lepton universality. The branching fraction for hadronic W decays is measured to be: B(W → hadrons) = 64.2−3.8+3.7 (stat.) ± 0.5 (syst.) %. Combining all final states the total cross section for W-pair production is measured to be: σWW = 12.27−1.32+1.41 (stat.) ± 0.23 (syst.) pb. The results are in good agreement with the Standard Model.

Pair-production of W bosons in e +e − interactions at [formula omitted] GeV

We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb −1, we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigma WW = 2.89 −0.70 +0.81(stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: M W = 80.80 −0.42 +0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.

Vector boson pair production in e−e− collisions with polarized beams

The W-boson pair production in e − e − collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.

W-BOSON PAIR PRODUCTION CROSS SECTION AND MEASUREMENT OF W-MASS

The W-pair production cross section in e+e− collision is investigated as a measuring tool for the W-mass. Against the recent argument, the cross section itself is not useful for determining the parameter of the electroweak theory. Also the leading logarithmic correction to the cross section is shown to be small.

Tests of real W-boson pair production

The energy spectrum and the angular distribution of the muon in the reaction e + e −→ W + W −→ q q ( two quark jets)+μ − ν μ are calculated in the framework of the Weinberg-Salam model. It is shown that the signal is well above the conventional backgrounds and thus could provide a clean signature for real W +W − production at LEP energies. Other distributions are briefly described.