Heavy Neutral Gauge Bosons Research Articles

SMEFT matching to Z′ models at dimension eight

Heavy neutral gauge bosons arise in many motivated models of beyond the Standard Model Physics. Experimental searches require that such gauge bosons are above the TeV scale in most models which means that the tools of effective field theories, in particular the Standard Model effective field theory (SMEFT), are useful. We match the SMEFT to models with heavy Z′ bosons, including effects of dimension-8 operators, and consider the restrictions on model parameters from electroweak precision measurements and from Drell Yan invariant mass distributions and forward-backward asymmetry, AFB, measurements at the LHC. The results demonstrate the model dependence of the resulting limits on SMEFT coefficients and the relatively small impact of including dimension-8 matching. In all cases, the limits from invariant mass distributions are stronger than from AFB measurements in the Z′ models we consider. Published by the American Physical Society 2024

A New Look at b → s Observables in 331 Models

Flavour changing neutral current (FCNC) processes are described by loop diagrams in the Standard Model (SM), while in 331 models, based on the gauge group SU(3)C×SU(3)L×U(1)X, they are dominated by tree-level exchanges of a new heavy neutral gauge boson Z′. By exploiting this feature, observables related to FCNC decays of K, Bd and Bs mesons can be considered in several variants of 331 models. The variants are distinguished by the value of a parameter β that plays a key role in this framework. Imposing constraints on the ΔF=2 observables, we select possible ranges for the mass of the Z′ boson in correspondence to the values β=±k/3, with k=1,2. The results are used to determine the impact of 331 models on b→s processes and on the correlations among them, in the light of new experimental data recently released.

Phenomenology of heavy neutral gauge boson at muon collider

Phenomenology of heavy neutral gauge boson at muon collider

Search for production of dark fermion candidates in association with heavy neutral gauge boson decaying to dimuon in proton-proton collisions at TeV using CMS open data* *Y. Mahmoud wishes to thank the Center for Theoretical Physics (CTP) at the British University in Egypt (BUE) for its continuous support, both financially and scientifically, for this work.

In this study, we conducted a search for dark matter using a part of the data recorded by the CMS experiment during run-I of the LHC in 2012 with a center of mass energy of 8 TeV and an integrated luminosity of 11.6 fb−1. These data were gathered from the CMS open data. Dark matter, in the framework of the simplified model (mono-Z ), can be produced from proton-proton collisions in association with a new hypothetical gauge boson, Z . Thus, the search was conducted in the dimuon plus large missing transverse momentum channel. One benchmark scenario of mono-Z , which is known as light vector, was used for interpreting the CMS open data. No evidence of dark matter was observed, and exclusion limits were set on the masses of dark matter and Z at 95% confidence level.

Search for the Z′ boson decaying to a right-handed neutrino pair in leptophobic U(1) models

The $U(1)$ extensions of the Standard Model contain a heavy neutral gauge boson ${Z}^{\ensuremath{'}}$. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic $U(1)$ extensions in which the ${Z}^{\ensuremath{'}}$ decays to right-handed neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic ${Z}^{\ensuremath{'}}$ and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a ${Z}^{\ensuremath{'}}$ at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the ${Z}^{\ensuremath{'}}$. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both same- and opposite-sign lepton pairs. Hence, the final state we study has a same-flavor opposite-sign lepton pair plus hadronically decaying boosted $W$ bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic ${Z}^{\ensuremath{'}}$ decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.

Unified explanation of the anomalies in semileptonic B decays and the W mass

The discrepancies between the measurements of rare (semi-)leptonic $B$ decays and the corresponding Standard Model predictions point convincingly towards the existence of new physics for which a heavy neutral gauge boson ($Z^\prime$) is a prime candidate. However, the effect of the mixing of the $Z^\prime$ with the SM $Z$, even though it cannot be avoided by any symmetry, is usually assumed to be small and thus neglected in phenomenological analyses. In this letter we point out that a mixing of the naturally expected size leads to lepton flavour universal contributions, providing a very good fit to $B$ data. Furthermore, the global electroweak fit is affected by $Z-Z^\prime$ mixing where the tension in the $W$ mass, recently confirmed and strengthened by the CDF measurement, prefers a non-zero value of it. We find that a $Z^\prime$ boson with a mass between $\approx 1-5\,\rm {TeV}$ can provide a unified explanations of the $B$ anomalies and the $W$ mass. This strongly suggests that the breaking of the new gauge symmetry giving raise to the $Z^\prime$ boson is linked to electroweak symmetry breaking with intriguing consequences for model building.

Search for Heavy Neutral Gauge Bosons in the Dilepton Channel in the CMS Experiment at the LHC

Search for Heavy Neutral Gauge Bosons in the Dilepton Channel in the CMS Experiment at the LHC

A heavy neutral gauge boson near the Z boson mass pole via third generation fermions at the LHC

We explore the physics of a new neutral gauge boson, (Z′), coupling to only third-generation particles and with a mass near the electroweak gauge boson mass poles. A Z′ boson produced by top quarks and decaying to tau leptons is considered. With a simple search strategy inspired by existing analyses of the standard model gauge boson production in association with top quarks, we show that the Large Hadron Collider has good exclusionary power over the model parameter space of the Z′ boson even at the advent of the high-luminosity era. It is shown that the tt¯Z′ process allows one to place limits on right-handed top couplings with a Z′ boson that preferentially couples to third generation fermions, which are at present very weakly constrained.

Anatomy of heavy gauge bosons in a left-right supersymmetric model

We perform a detailed study of the various decay channels of the heavy charged and neutral gauge bosons ($W_R$ and $Z_R$ respectively) in a left-right supersymmetric (LRSUSY) framework. The decay branching ratios of the $W_R$ and $Z_R$ bosons depend significantly on the particle spectrum and composition of the SUSY states. We show several combinations of mass spectrum for the SUSY particles to facilitate the decay of these heavy gauge bosons into various combinations of final states. Finally, we choose two benchmark points and perform detailed collider simulations for these heavy gauge bosons in the context of the high energy and high luminosity run of the large hadron collider. We analyze two SUSY cascade decay channels -- mono-$W$ + $\slashed{E}_T$ and mono-$Z$ + $\slashed{E}_T$ along with the standard dilepton and dijet final states. Our results show that the existence of these heavy gauge bosons can be ascertained in the direct decay channels of dilepton and dijet whereas the other two channels will be required to establish the supersymmetric nature of this model.

Constraining heavy neutral gauge boson Z′ in the 3 - 3 - 1 models by weak charge data of Cesium and proton

The recent experimental data of the weak charges of Cesium and proton is analyzed in the framework of the models based on the SU(3)C×SU(3)L×U(1)X (3-3-1) gauge group, including the 3-3-1 model with CKS mechanism (3-3-1CKS) and the general 3-3-1 models with arbitrary β (3-3-1β) with three Higgs triplets. We will show that at the TeV scale, the mixing among neutral gauge bosons plays significant effect. Within the present values of the weak charges of Cesium and proton we get the lowest mass bound of the extra heavy neutral gauge boson to be 1.27 TeV. The results derived from the weak charge data, perturbative limit of Yukawa coupling of the top quark, and the relevant Landau poles favor the models with β=±13 and β=0 while ruling out the ones with β=±3. In addition, there are some hints showing that in the 3-3-1 models, the third quark family should be treated differently from the first twos.

Search for lepton flavour violation with the ATLAS experiment

Lepton flavour violation (LFV) is a striking signature of potential beyond the Standard Model physics. The search for LFV with the ATLAS detector is reported in searches focusing on the decay of the Higgs boson, the Z boson and of a heavy neutral gauge boson, Z’, using pp collisions data with a center of mass energy of 8 TeV and 13 TeV.

Minimally extended left-right symmetric model for dark matter with U(1) portal

A minimal extension of the left-right symmetric model for neutrino masses that includes a vector-like singlet fermion dark matter (DM) is presented with the DM connected to the visible sector via a gauged U(1) portal. We discuss the symmetry breaking in this model and calculate the mass and mixings of the extra heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to both standard model particles as well to dark matter. We calculate the relic density of the singlet fermion dark matter and its direct detection cross section and use these constraints to obtain the allowed parameter range for the new gauge coupling and the dark matter mass.

Fermiophobic gauge boson phenomenology in 221 models

Models with extra gauge symmetry are well-motivated extensions of the Standard Model. In this paper, we study an extended gauge model with a heavy neutral gauge boson $Z'$ which is fermiophobic. Thus, the production of such particles can occur via vector boson fusion, with subsequent decays into $WW$ or $Zh$. We investigate the collider phenomenology of such $Z'$s in the context of both the 14 TeV LHC and the future CLIC. We find that looking at $\ell\ell b b$ final states provides a rich opportunity to discover such new vector bosons where conventional search strategies in the dilepton channel would fail. In particular, we optimize our analysis by putting in kinematic cuts deriving model-independent values of $\sigma\times$BR needed for a 5$\sigma$ discovery at the LHC. We then translate this into the parameter space of a specific model for illustration purpose -- our results show that fermiophobic $Z'$s are discoverable in the $\ell\ell b b$ channel for wide range of parameter values.

Bottom-quark fusion processes at the LHC for probing Z′ models and B -meson decay anomalies

We investigate models of a heavy neutral gauge boson Z' which could explain anomalies in B meson decays reported by the LHCb experiment. In these models, the Z' boson couples mostly to third generation fermions. We show that bottom quarks arising from gluon splitting can fuse into Z' as an essential production mechanism at the LHC, thereby allowing to probe these models. The study is performed within a generic framework for explaining the B anomalies that can be accommodated in well motivated models. The flavor violating b s coupling associated with Z' in such models produces lower bound on the production cross-section which gives rise to a cross-section range for such scenarios for the LHC to probe. Results are presented in Z' -> $\mu \mu$ decays with at least one bottom-tagged jet in its final state. Some parts of the model parameter space become constrained by the existing dimuon-resonance searches by the ATLAS and CMS collaborations. However, the requirement of one or two additional bottom-tagged jets in the final state would allow for probing a larger region of the parameter space of the models at the ongoing LHC program.

Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb\u22121 of pp collisions at sqrt{s}=13 TeV with the ATLAS detector

A search for heavy neutral Higgs bosons and Z′ bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb−1 from proton-proton collisions at sqrt{s}=13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to τ+τ− with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for Z′ bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude tan β > 1.0 for mA = 0.25 TeV and tan β > 42 for mA = 1.5 TeV at the 95% confidence level. For the Sequential Standard Model, ZSSM′ with mZ′ < 2.42 TeV is excluded at 95% confidence level, while ZNU′ with mZ ′ < 2.25 TeV is excluded for the non-universal G(221) model that exhibits enhanced couplings to third-generation fermions.

Searching for new heavy neutral gauge bosons using vector boson fusion processes at the LHC

New massive resonances are predicted in many extensions to the Standard Model (SM) of particle physics and constitutes one of the most promising searches for new physics at the LHC. We present a feasibility study to search for new heavy neutral gauge bosons using vector boson fusion (VBF) processes, which become especially important as the LHC probes higher collision energies. In particular, we consider the possibility that the discovery of a $Z'$ boson may have eluded searches at the LHC. The coupling of the $Z'$ boson to the SM quarks can be small, and thus the $Z'$ would not be discoverable by the searches conducted thus far. In the context of a simplified phenomenological approach, we consider the $Z'\to\tau\tau$ and $Z'\to\mu\mu$ decay modes to show that the requirement of a dilepton pair combined with two high $p_{T}$ forward jets with large separation in pseudorapidity and with large dijet mass is effective in reducing SM backgrounds. The expected exclusion bounds (at 95\% confidence level) are $m(Z') < 1.8$ TeV and $m(Z') < 2.5$ TeV in the $\tau\tau j_{f}j_{f}$ and $\mu\mu j_{f}j_{f}$ channels, respectively, assuming 1000 fb$^{-1}$ of 13 TeV data from the LHC. The use of the VBF topology to search for massive neutral gauge bosons provides a discovery reach with expected significances greater than 5$\sigma$ (3$\sigma$) for $Z'$ masses up to 1.4 (1.6) TeV and 2.0 (2.2) TeV in the $\tau\tau j_{f}j_{f}$ and $\mu\mu j_{f}j_{f}$ channels.

A calculation of the ZH → γH decay in the Littlest Higgs Model

New heavy neutral gauge bosons are predicted in many extensions of the Standard Model, those new bosons are associated with additional gauge symmetries. We present a preliminary calculation of the branching ratio decay for heavy neutral gauge bosons (Zh) into γH in the most popular version of the Little Higgs models. The calculation involves the main contributions at one-loop level induced by fermions, scalars and gauge bosons. Preliminary results show a very suppressed branching ratio of the order of 10-6.

Diphoton channel at the LHC experiments to find a hint for a new heavy gauge boson

Recently there has been a huge interest in the diphoton excess around 750 GeV reported by both ATLAS and CMS collaborations, although the newest analysis with more statistics does not seem to support the excess. Nevertheless, the diphoton channel at the LHC experiments are a powerful tool to probe a new physics. One of the most natural explanations of a diphoton excess, if it occurs, could be a new scalar boson with exotic colored particles. In this setup, it would be legitimate to ask what is the role of this new scalar in nature. A heavy neutral gauge boson [Formula: see text] is one of the traditional targets of the discovery at the collider experiments with numerous motivations. While the Landau–Yang theorem dictates the diphoton excess cannot be this spin-1 gauge boson, there is a strong correlation of a new heavy gauge boson and a new scalar boson which provides a mass to the gauge boson being at the same mass scale. In this paper, we point out a simple fact that a new scalar with a property similar to the recently highlighted 750 GeV would suggest an existence of a TeV scale [Formula: see text] gauge boson that might be within the reach of the LHC Run 2 experiments. We take a scenario of the well-motivated and popular gauged [Formula: see text] symmetry and require the gauge coupling unification to predict the mass and other properties of the [Formula: see text] and illustrate the discovery of the [Formula: see text] would occur during the LHC experiments.

Drell-Yan production of multi Z ′-bosons at the LHC within Non-Universal ED and 4D Composite Higgs Models

The Drell-Yan di-lepton production at hadron colliders is by far the preferred channel to search for new heavy spin-1 particles. Traditionally, such searches have exploited the Narrow Width Approximation (NWA) for the signal, thereby neglecting the effect of the interference between the additional Z'-bosons and the Standard Model Z and {\gamma}. Recently, it has been established that both finite width and interference effects can be dealt with in experimental searches while still retaining the model independent approach ensured by the NWA. This assessment has been made for the case of popular single Z'-boson models currently probed at the CERN Large Hadron Collider (LHC). In this paper, we test the scope of the CERN machine in relation to the above issues for some benchmark multi Z'-boson models. In particular, we consider Non-Universal Extra Dimensional (NUED) scenarios and the 4-Dimensional Composite Higgs Model (4DCHM), both predicting a multi-Z' peaking structure. We conclude that in a variety of cases, specifically those in which the leptonic decays modes of one or more of the heavy neutral gauge bosons are suppressed and/or significant interference effects exist between these or with the background, especially present when their decay widths are significant, traditional search approaches based on the assumption of rather narrow and isolated objects might require suitable modifications to extract the underlying dynamics.

B−Lheavy neutrinos and neutral gauge bosonZ′at the LHC

We explore possible signatures for heavy neutrinos and neutral gauge boson, Z', in TeV scale B-L extension of the Standard Model (BLSM) with inverse seesaw mechanisms at the Large Hadron Collider. We show that due to new decay channels of Z' into heavy/inert neutrinos, the LHC stringent bounds imposed on Z' mass can be significantly relaxed. We analyze the pair production of heavy neutrinos decaying to four leptons plus two neutrinos, four jets plus two leptons, or three leptons plus two jets and one neutrino. We show that the 4l + 2 nu is the most promising decay channel for probing both Z' and heavy neutrinos at the LHC.