Narrow Results

The mass of Z′ boson is considered in a flavor-independent phenomenological potential model. We have used the low energy parameters and the estimated value so obtained is accessible to experiments at low energies.

We study the effect of both Z and Z′-mediated flavor-changing neutral current (FCNC) on the B_d→ℓ⁺ℓ^-, (ℓ = μ, τ) rare decay. We find that the branching ratio can be larger by order two from its Standard Model (SM) value due to the effect of both Z and Z′-mediated FCNC, though the major contribution comes from Z boson and provides signals for new physics beyond the SM.

From several neutrino oscillation experiments, we understand now that neutrinos have mass. However, we really do not know what mechanism is responsible for producing this neutrino mass. Current or planned neutrino experiments utilize neutrino beams and long-baseline detectors to explore flavor mixing but do not address the question of the origin of neutrino mass. In order to begin answering that question, neutrino interactions need to be explored at much higher energies. This paper outlines a program to explore neutrinos and their interactions with various particles through a series of experiments involving colliding neutrino beams.

The cross section of the μ⁺μ^- pair production in pp-collisions at the LHC is calculated with account of the Z' boson induced by the minimal four-color quark–lepton symmetry (MQLS). The μ⁺μ^- invariant mass spectrum with account of the MQLS Z' boson is analyzed in dependence on the Z' mass. The mass region for the MQLS Z' boson observable at the LHC is found in dependence on the significance and on the integrated luminosity.

The search for neutral resonances at the energy frontier has a long and illustrious history, resulting in multiple discoveries. The canonical search scans the reconstructed invariant mass distribution of identified fermion pairs. Two recent analyses from the CDF experiment at the Fermilab Tevatron have applied novel methods to resonance searches. One analysis uses simulated templates to fit the inverse mass distribution of muon pairs, a quantity with approximately constant resolution for momenta measured with a tracking detector. The other analysis measures the angular distribution of electron pairs as a function of dielectron mass, gaining sensitivity over a probe of the mass spectrum alone. After reviewing several models that predict new neutral resonances, we discuss these CDF analyses and potential future applications.

Recently, some small hints of lepton flavor violating (LFV) decays have been probed in different colliders and accelerators. Although these processes are forbidden in the Standard Model (SM), observation of LFV decays are considered as good probes to test theory beyond the SM. In this paper, we study some LFV decays, e.g. three-body decay channels of $\mu$ lepton like $\mu \to 3e$, $\mu \to e\nu \bar{\nu }$ and two-body decays of B meson and $\tau$ lepton like $B_{s,d}\to {\mu }^{\pm }{e}^{\mp }$ and $\tau \to e\varphi$ in $Z^{\prime }$ model. We calculate the branching ratio of the above decays considering the effect of both $Z$ and $Z^{\prime }$-mediated flavor-changing neutral-current (FCNC).

In the Left–Right Symmetric Model, and mass differences are considered, taking the effect of the triplet Higgs, W_R and Z′ bosons in the effective Hamiltonian in Vacuum Insertion Method and in Heavy Quark Effective Theory. It is observed that the masses M_R, M_H, and M_Z′ are well within the experimental search in the forthcoming accelerators.

We study the effect of both Z and Z′ mediated flavor-changing neutral currents (FCNCs) on the Λ_b→Λℓ⁺ℓ^-(ℓ = μ, τ) rare decay. We find the branching ratio is reasonably enhanced from its Standard Model value due to the effect of both Z and Z′ mediated FCNCs, and gives the possibility of new physics beyond the Standard Model. The contribution of Z′ boson depends upon the precise value of M_Z′.

The paper deals with an approach to the model-independent searching for the Z' gauge boson as a virtual state in scattering processes. The relations between the Z' couplings to fermions covering a wide class of models beyond the Standard Model are found and used. They reduce in an essential way the number of parameters to be fitted in experiments. Special observables which uniquely pick out the Z' at energies of LEP and ILC colliders in different leptonic processes are introduced and the data of LEP experiments are analyzed. The Z' couplings to leptons and quarks are estimated at 95% confidence level. At this level, the LEP data are compatible with the existence of the Z' with the mass m_Z′ ~ 1–1.2 TeV. These estimates may serve as a guide for experiments at the Tevatron and/or LHC. A comparison with other approaches and results is given.

The model-independent constraints on the Abelian Z′ couplings from the LEP data are applied to estimate the Z′ production in experiments at the Tevatron and LHC. The Z′ total and partial decay widths are analyzed. The results are compared with model-dependent predictions and present experimental data from the Tevatron. If we assume the 1–2σ hints from the LEP data to be a signal of the Abelian Z′ boson, then the Tevatron data constrain the Z′ mass between 400 GeV and 1.2 TeV.

In recent years, B_s →τ⁺τ^- rare decay has attracted a lot of attention since it is very sensitive to the structure of standard model (SM) and potential source of new physics beyond SM. In this paper, we study the effect of both Z and Z′-mediated flavor-changing neutral currents on the B_s →τ⁺τ^- decay. We find the branching ratio B(B_s→τ⁺τ^-) is enhanced relative to SM prediction, which would help to explain the recently observed CP-violation from like-sign dimuon charge asymmetry in the B system.

In this paper, we investigate the Drell–Yan process with the intermediate heavy Z′ boson. We use a general approach to the Abelian Z′ that utilizes the renormalization-group relations between the Z′ couplings and allows to reduce the number of unknown Z′ parameters significantly. In a newly proposed strategy, we estimate the LHC-driven constraints for the Z′ couplings to lepton and quark vector currents. To do this, we calculate the Z′-related contribution in the narrow-width approximation and compare the obtained values to the experimental data presented by the ATLAS and CMS collaborations. Our method allows to estimate the values of Z′ couplings to the u and d quarks and to final-state leptons.

Processes τ→lγ, τ→lll with l = e, μ and μ(τ) →e (μ) γ are evaluated in the framework of a model based on the extended symmetry gauge SU(3)_c ⊗SU(3)_L ⊗U(1)_Y with a leptonic sector consisting of five triplets. Lepton flavor violating processes are allowed at tree level in this model through the new Z′ gauge boson. We obtained bounds for the mixing angles in the leptonic sector of the model, considering the experimental measurements of the processes from the BELLE and the BABAR collaborations.

To detect off-shell Abelian Z′ boson in e⁺e^-→μ⁺μ^-, we propose one-parameter observables with the best value-to-uncertainty ratio. The observables are constructed by angular integration of the differential cross-section with smooth weight functions. The value-to-uncertainty ratio is used as a criterion to select the unique weight function leading to the observable with the best statistical power for data analysis. The observables allow to select either vector or axial-vector Z′ couplings to leptons. The obtained observable can be useful in future experiments at lepton colliders such as the ILC.

The integral observables for model-independent detections of Abelian Z′ gauge boson in e⁺e^- → μ⁺μ^-(τ⁺τ^-) process with unpolarized beams at the ILC energies are proposed. They are based on the differential cross-section of deviations from the standard model predictions calculated with a low energy effective Lagrangian and taking into consideration the relations between the Z′ couplings to the fermions derived already. Due to these relations, the cross-section exhibits angular distribution giving a possibility for introducing one- or two-parameter observables which effectively fit the mass m_Z′, the axial-vector and the product of vector couplings v_ev_μ(v_ev_τ). A discovery reach for the Z′ is estimated for two of introduced observables. Determination of the basic Z′ model is discussed. Comparison with other results and approaches is given.

The rare decays $B_{s,d}^{\ast }\to l^{+}{l}^{-}$ are important to probe the flavor sector of the standard model and to search new physics beyond the SM. Unlike pseudoscalar $B$ meson, the leptonic decays of vector $B_{s,d}^{\ast }$ mesons are not chirally suppressed which compensates for their short lifetimes, and results in significant branching ratios. In this paper, we estimate the branching ratios of $B_{s,d}^{\ast }\to l^{+}{l}^{-}$$(l=e,\mu )$ rare decays in $Z^{\prime }$ model which is an extension of the SM with an extra $U{(1)}^{\prime }$ gauge symmetry. We find that the branching ratios are increased from their corresponding standard model values and vary with the mass of $Z^{\prime }$ boson. The lower the mass of $Z^{\prime }$ boson, the higher is the branching ratio.

We investigate $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ decays in a nonuniversal $Z^{\prime }$ model derived from the extension of the Standard Model (SM). Considering the $Z^{\prime }$-mediated flavor-changing neutral current (FCNC) effects, we calculate the branching ratio and forward–backward asymmetry $(A_{\mathrm{\text{FB}}})$ for $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ decay processes. We compare the obtained results with predictions of the SM and discuss the sensitivity of the observables to $Z^{\prime }$ boson coupling parameters. We find that the branching ratios are enhanced by one order from SM predictions in $Z^{\prime }$ model scenario. We also observe that the variation of forward–backward asymmetry with the $Z^{\prime }$ boson coupling parameters portrays discrimination between NP effects and SM results.

Baryonic decays induced by $b\to s{l}^{+}{l}^{-}$ quark transition is an important area of interest nowadays to probe the sensitivities of new physics (NP). The exploration of the baryonic channels was prompted by the observation of ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{\mu }^{+}{\mu }^{-}$ decays at the accelerators. Motivated by the recent experimental studies of baryonic decays, we have studied various polarization asymmetries for ${\mathrm{\Sigma }}_b$ baryon in the model beyond the standard model (SM). From the theoretical inspections of branching ratios for ${\mathrm{\Sigma }}_b\to \mathrm{\Sigma }{l}^{+}{l}^{-}$ channels in the SM indicate that these decays can be observed at the colliders. In this paper, we have studied the various $\mathrm{\Sigma }$ lepton polarization asymmetries within the whole allowed kinematic region for all three leptonic channels considering the effect of nonuniversal $Z^{\prime }$ boson. We expect that the obtained results for ${\mathrm{\Sigma }}_b$ decays will help the experimental groups investigate these decays at colliders and will probe NP with heavy baryons.