Charged Gauge Bosons Research Articles

Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb−1 of pp collisions at [formula omitted] using the ATLAS detector

The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W′), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb−1. No excess above Standard Model expectations is observed. A W′ with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 TeV.

Limits on the left-right symmetry scale and heavy neutrinos from early LHC data

We use the early Large Hadron Collider data to set the lower limit on the scale of Left-Right symmetry, by searching for the right-handed charged gauge boson $W_R$ via the final state with two leptons and two jets, for 33/pb integrated luminosity and 7 TeV center-of-mass energy. In the absence of a signal beyond the Standard Model background, we set the bound M_WR > 1.4 TeV at 95% C.L.. This result is obtained for a range of right-handed neutrino masses of the order of few 100 GeV, assuming no accidental cancelation in right-handed lepton mixings.

Probing theWL′WHandWR′WHinteractions at LHC

Many new physics models predict the existence of TeV-scale charged gauge boson ${W}^{\ensuremath{'}}$ together with Higgs-boson(s). We study the ${W}^{\ensuremath{'}}WH$ interaction and explore the angular distribution of charged leptons to distinguish ${W}_{R}^{\ensuremath{'}}WH$ from ${W}_{L}^{\ensuremath{'}}WH$ in the $pp\ensuremath{\rightarrow}HW\ensuremath{\rightarrow}b\overline{b}l\ensuremath{\nu}$ process at the LHC. It is found that a new type forward-backward asymmetry (${A}_{\mathrm{FB}}$) relating to the angle between the direction of the charged lepton in the $W$ rest frame and that of the reconstructed ${W}^{\ensuremath{'}}$ in the laboratory frame is useful to investigate the properties of ${W}^{\ensuremath{'}}WH$ interaction. We analyze the standard model backgrounds and develop a set of cuts to highlight the signal and suppress the backgrounds at LHC. We find that ${A}_{\mathrm{FB}}$ can reach $0.03(\ensuremath{-}0.07)$ for ${W}_{R}^{\ensuremath{'}}({W}_{L}^{\ensuremath{'}})$ production at $\sqrt{S}=14\text{ }\text{ }\mathrm{TeV}$.

Search for high-mass states with one lepton plus missing transverse momentum in proton–proton collisions at [formula omitted] with the ATLAS detector

The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W′,W⁎), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb−1. No excess beyond standard model expectations is observed. A W′ with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W⁎ (charged chiral boson) for masses below 1.35 TeV.

GRADED LIE ALGEBRA AND THE SU(3)L⊗U(1)N GAUGE MODEL

A classical gauge model based on the Lie group SU (3)L⊗ U (1)N with exotic quarks is reformulated within the formalism of nonassociative geometry associated with an L cycle. The N charges of the fermionic particles and the related parameter constraints are algebraic consequences and are uniquely determined. Moreover, the number of scalar particles is dictated by the nonassociativity of the geometry. As a byproduct of this formalism, the Weinberg angle θw, scalar, charged and neutral gauge boson masses, as well as the mixing angles, are derived. Furthermore, various expressions for the vector and axial couplings of the quarks and leptons with the neutral gauge bosons and lower bounds of the very heavy gauge bosons are obtained.

Z′production at the LHC in the four-site Higgsless model

We study the phenomenology of the neutral gauge sector of the four-site Higgsless model, based on the $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{1}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{2}\ifmmode\times\else\texttimes\fi{}U(1{)}_{Y}$ gauge symmetry, at present colliders. The model predicts the existence of two neutral and four charged extra gauge bosons, ${Z}_{1,2}$ and ${W}_{1,2}^{\ifmmode\pm\else\textpm\fi{}}$. We expand and update a previous study, by concentrating on the neutral sector. We derive new limits on ${Z}_{1,2}$-boson masses and couplings from recent direct searches at the Tevatron. We moreover estimate the discovery potential at the Tevatron with a project luminosity $L=10\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, and at the 7 TeV LHC with $L=1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. In contrast to other Higgsless theories characterized by almost fermiophobic extra gauge bosons, the four-site model allows sizable ${Z}_{1,2}$-boson couplings to standard model fermions. Owing to this feature, we find that in the next 2 years the extra ${Z}_{1,2}$ bosons could be discovered in the favored Drell-Yan channel at the 7 TeV LHC for ${Z}_{1,2}$ masses in the TeV region, depending on model parameters.

Noncommutative standard model and polarization in charged gauge boson production at the LHC

We study the pair production of charged gauge bosons at the LHC in a noncommutative extension of the standard model. We use angular distributions in the decays of the gauge bosons to partially reconstruct polarized cross sections. We use this, together with CP considerations, to construct more sensitive observables that allow to separate space-time from space-space noncommutativities.

Chiral couplings ofW′and top quark polarization at the LHC

If a TeV-scale charged gauge boson (W') is discovered at the Large Hadron Collider (LHC), it will become imperative to determine its chiral couplings to standard model (SM) fermions in order to learn about the underlying theory containing the W'. We describe the reconstruction of the t, b decay mode of the W' at the LHC, and identify various kinematic observables such as the angular distributions of the top quark and the lepton resulting from top decay that can be used to disentangle the chiral couplings of the W' to SM fermions. We demonstrate by presenting analytical expressions, numerical simulations, as well as intuitive illustrations for these observables at the LHC that among the SM fermions, the polarized top quark can most directly probe the chirality of such couplings.

Two loop electroweak corrections from heavy fermions to b → s + γ

Applying an effective Lagrangian method and an on-shell scheme, we analyze the electroweak corrections to the rare decay b → s + γ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in the inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of B → Xsγ can reach 5% as the energy scale of new physics ΛNP = 200 GeV.

Left-right symmetry at LHC

We revisit the issue of the limit on the scale of Left-Right symmetry breaking. We focus on the minimal SU(2)_L x SU(2)_R x U(1)_B-L gauge theory with the seesaw mechanism and discuss the two possibilities of defining Left-Right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, M_WR>2.5TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on M_WR is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the Standard Model and CP-violation in the $B$-sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation.

Heavy Charged Gauge Bosons with General CP Violating Couplings

Heavy gauge bosons such as W′ are expected to exist in many extensions of the Standard Model. In this paper, the most general Lagrangian for the interaction of W′ with top and bottom quarks is considered. This Lagrangian consists of V–A and V+A structure with in general complex couplings. Such interactions produce an Electric Dipole Moment (EDM) for the top quark at one loop level. We predict the allowed ranges for the mass and couplings of W′ by using the upper limit on the top quark EDM.

LHC signals for coset electroweak gauge bosons in warped/composite pseudo-Goldstone boson Higgs models

The framework of a warped extra dimension with the Standard Model (SM) fields propagating in it is a very well-motivated extension of the SM since it can address both the Planck-weak and flavor hierarchy problems of the SM. Within this framework, solution to the little hierarchy problem motivates extending the SM electroweak (EW) 5D gauge symmetry in such a way that its breakdown to the SM delivers the SM Higgs boson. We study signals at the large hadron collider (LHC) for the extra EW (called coset) gauge bosons, a fundamental ingredient of this framework. The coset gauge bosons, due to their unique EW gauge quantum numbers [doublets of SU(2)_L], do not couple at leading order to two SM particles. We find that, using the associated production of the charged coset gauge bosons via their coupling to SM bottom quark and a (light) KK top quark, the LHC can have a 3\sigma reach of \sim 2 (2.6) TeV for the coset gauge boson masses with \sim 100 (1000) fb^{-1} luminosity. Since current theoretical framework(s) suggest an {\em indirect} lower limit on coset gauge boson masses of >3 TeV, luminosity or energy upgrade of LHC is likely to be crucial in observing these states.

Heavy fermions and two loop electroweak corrections to b → s + γ

Applying effective Lagrangian method and on-shell scheme, we analyze the electroweak corrections to the rare decay $b\rightarrow s+\gamma$ from some special two loop diagrams in which a closed heavy fermion loop is attached to the virtual charged gauge bosons or Higgs. At the decoupling limit where the virtual fermions in inner loop are much heavier than the electroweak scale, we verify the final results satisfying the decoupling theorem explicitly when the interactions among Higgs and heavy fermions do not contain the nondecoupling couplings. Adopting the universal assumptions on the relevant couplings and mass spectrum of new physics, we find that the relative corrections from those two loop diagrams to the SM theoretical prediction on the branching ratio of $B\rightarrow X_{_s}\gamma$ can reach 5% as the energy scale of new physics $\Lambda_{_{\rm NP}}=200$ GeV.

LHC signals for warped electroweak charged gauge bosons

We study signals at the LHC for the Kaluza-Klein (KK) excitations of electroweak charged gauge bosons in the framework of the standard model (SM) fields propagating in the bulk of a warped extra dimension. Such a scenario can solve both the Planck-weak and flavor hierarchy problems of the SM. There are two such charged states in this scenario with couplings to light quarks and leptons being suppressed relative to those in the SM, whereas the couplings to top/bottom quarks are enhanced, similar to the case of electroweak neutral gauge bosons previously studied. However, unlike the case of electroweak neutral gauge bosons, there is no irreducible QCD background (including pollution from possibly degenerate KK gluons) for decays to top+bottom final states so that this channel is useful for the discovery of the charged states. Moreover, decays of electroweak charged gauge bosons to longitudinal W, Z and Higgs are enhanced just as for the neutral bosons. However, unlike for the neutral gauge bosons, the purely leptonic (and hence clean) decay mode of the WZ is fully reconstructible so that the ratio of the signal to the SM (electroweak) background can potentially be enhanced by restricting to the resonance region more efficiently. Wemore » show that such final states can give sensitivity to 2(3) TeV masses with an integrated luminosity of 100(300) fb{sup -1}. We emphasize that improvements in discriminating a QCD jet from a highly boosted hadronically decaying W, and a highly boosted top jet from a bottom jet will enhance the reach for these KK particles, and that the signals we study for the warped extra dimensional model might actually be applicable also to a wider class of nonsupersymmetric models of electroweak symmetry breaking.« less

Electroweak and flavour structure of a warped extra dimension with custodial protection

We present the electroweak and flavour structure of a model with a warped extra dimension and the bulk gauge group SU(3) x SU(2)_L x SU(2)_R x P_LR x U(1)_X. The presence of SU(2)_R implies an unbroken custodial symmetry in the Higgs system allowing to eliminate large contributions to the T parameter, whereas the P_LR symmetry and the enlarged fermion representations provide a custodial symmetry for flavour diagonal and flavour changing couplings of the SM Z boson to left-handed down-type quarks. We diagonalise analytically the mass matrices of charged and neutral gauge bosons including the first KK modes. We present the mass matrices for quarks including heavy KK modes and discuss the neutral and charged currents involving light and heavy fields. We give the corresponding complete set of Feynman rules in the unitary gauge.

Bilepton contributions to the neutrinoless double beta decay in the economical 3-3-1 model

Possible contributions of the bilepton to the neutrinoless double beta $(\beta\beta)_{0\nu}$ decay in the economical 3-3-1 model are discussed. We show that the $(\beta\beta)_{0\nu}$ decay in this model is due to both sources--Majorana $ _{L}$ and Dirac $ _{D}$ neutrino masses. If the mixing angle between charged gauge bosons, the standard model $W$ and bilepton $Y$, is in range of the ratio of neutrino masses $ _{L}/ _{D}$, both the Majorana and Dirac masses simultaneously give contributions dominant to the decay. As results, constraints on the bilepton mass are also given.

Effect of the neutrino magnetic moment on the properties of the muon

The effect of the neutrino dipole magnetic moment on the properties of the muon is investigated within the standard model of electroweak interactions and a model based on the SU(2)L × SU(2)R × U(1)B-L gauge group (left-right model). In the case of the Dirac neutrino, muon decay through the channel µ− → e−γ is studied with allowance for the neutrino dipole magnetic moment. It is shown that, both in the standard model supplemented with an SU(2)L right-handed neutrino singlet and in the standard model featuring two doublets of Higgs fields, radiative muon decay is unobservable. In the left-right model, the contributions of diagrams associated with the neutrino dipole magnetic moment become significant only in the case of a mutual compensation of the contributions of diagrams involving the electromagnetic vertices of charged gauge bosons and singly charged Higgs bosons. At specific values of the parameters of the left-right model, one can then obtain an experimental upper limit on the branching fraction of this reaction. The contributions of the neutrino dipole magnetic moment to the muon anomalous magnetic moment are found for the Dirac and the Majorana neutrino. It is established that, both in the standard model and in the left-right model, values of the neutrino anomalous magnetic moment that are required for explaining the (g − 2)µ anomaly are in excess of the theoretical predictions for this moment.

One-loop corrections to theSparameter in the four-site model

We compute the leading chiral-logarithmic corrections to the $S$ parameter in the four-site Higgsless model. In addition to the usual electroweak gauge bosons of the standard model, this model contains two sets of heavy charged and neutral gauge bosons. In the continuum limit, the latter gauge bosons can be identified with the first excited Kaluza-Klein states of the ${W}^{\ifmmode\pm\else\textpm\fi{}}$ and $Z$ bosons of a warped extra-dimensional model with an $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{R}\ifmmode\times\else\texttimes\fi{}U(1{)}_{X}$ bulk gauge symmetry. We consider delocalized fermions and show that the delocalization parameter must be considerably tuned from its tree-level ideal value in order to reconcile experimental constraints with the one-loop results. Hence, the delocalization of fermions does not solve the problem of large contributions to the $S$ parameter in this class of theories and significant contributions to $S$ can potentially occur at one-loop.

Probing doubly charged Higgs bosons ine+e−colliders at the ILC and the CLIC in a 3-3-1 model

The $\mathrm{SU}(3{)}_{L}\ensuremath{\bigotimes}\mathrm{U}(1{)}_{N}$ electroweak model predicts new Higgs bosons beyond the one of the standard model. In this work we investigate the signature and production of doubly charged Higgs bosons in the ${e}^{\ensuremath{-}}{e}^{+}$ International Linear Collider and in the CERN Linear Collider. We compute the branching ratios for the doubly charged gauge bosons of the model.

Charged bilepton pair production at LHC including exotic quark contribution

The production of W + W − pair in hadron colliders was calculated up to loop corrections by some authors in the Electroweak Standard Model (SM) framework. This production was also calculated, at the tree level, in some extensions of the SM such as the vector singlet, the fermion mirror fermion and the vector doublet models by considering the contributions of new neutral gauge bosons and exotic fermions. The obtained results for e + e − and pp collisions pointed out that the new physics contributions are quite important. This motivates us to calculate the production of a more massive charged gauge boson predicted by the SU ( 3 ) C × SU ( 3 ) L × U ( 1 ) X model (3-3-1 model). Thus, the aim of the present paper is to analyze the role played by of the extra gauge boson Z ′ and of the exotic quarks, predicted in the minimal version of the 3-3-1 model, by considering the inclusive production of a pair of bileptons ( V ± ) in the reaction p + p → V + + V − + X , at the Large Hadron Collider (LHC) energies. Our results show that the correct energy behavior of the elementary cross section follows from the balance between the contributions of the extra neutral gauge boson with those from the exotic quarks. The extra neutral gauge boson induces flavor-changing neutral currents (FCNC) at tree level, and we have introduced the ordinary quark mixing matrices for the model when the first family transforms differently to the other two with respect to SU ( 3 ) L . We obtain a huge number of heavy bilepton pairs produced for two different values of the center of mass energy of the LHC.