In this note, I examine the possible consequences for high energy colliders of a Z-prime interpretation of the LHCb anomaly observed in the K*mu+mu- final state. Two examples are elaborated in the framework of the so-called 331 model. In the first one it is shown that LEP2 provides the tightest lower mass limit for the Z-prime boson, above 8 TeV, while in the second one the lower mass limit is set by ATLAS/CMS to about 3 TeV. It is then shown that precision measurements at ILC 500 GeV can fully explore the underlying structure of the model by measuring the fermion final states separately: leptons, charm, beauty and top final states. Z-prime-Z mixing can also be substantial, thus leading to possible effects almost observable at LEP1 and which can be precisely measured at GigaZ. Discovery prospects for heavy bosons and heavy fermions at LHC are also discussed .
We examine current collider constraints on some simple $Z^\prime$ models that fit neutral current $B-$anomalies, including constraints coming from measurements of Standard Model (SM) signatures at the LHC. The `MDM' simplified model is not constrained by the SM measurements but {\em is} strongly constrained by a 139 fb$^{-1}$ 13 TeV ATLAS di-muon search. Constraints upon the `MUM' simplified model are much weaker. A combination of the current $B_s$ mixing constraint and ATLAS' $Z^\prime$ search implies $M_{Z^\prime}>1.2$ TeV in the Third Family Hypercharge Model example case. LHC SM measuremen…
We further investigate the case where new physics in the form of a massive $Z^\prime$ particle explains apparent measurements of lepton flavour non-universality in $B \rightarrow K^{(\ast)} l^+ l^-$ decays. Hadron collider sensitivities for direct production of such $Z^\prime$s have been previously studied in the narrow width limit for a $μ^+ μ^-$ final state. Here, we extend the analysis to sizeable decay widths and improve the sensitivity estimate for the narrow width case. We estimate the sensitivities of the high luminosity 14 TeV Large Hadron Collider (HL-LHC), a high energy 27 TeV LHC (H…
We consider the capability of a future high energy $e^+ e^-$ collider to search for the $Z^\prime$ bosons associated with a $U(1)^\prime$ gauge extension of the Standard Model. Even for $Z^\prime$ masses well above the center of mass energy of the collider, the rates of production of $e^+ e^-$, $μ^+ μ^-$, unflavored jets, and $b$-tagged jets can reveal the presence of virtual $Z^\prime$ exchange. We consider collider configurations with center-of-mass energy 200, 300, and 500 GeV, and show how various classes of $Z^\prime$ model-lines can be probed with $100~{\rm fb}^{-1}$ of integrated lumino…
The associated production of a $Z^{\prime}$ and a final hard photon in high energy electron-positron colliders is studied. It is shown that the hard photon spectrum contains useful information on the $Z^{\prime}$ properties. This remark suggests that, if a new neutral gauge boson exists for $M_{Z^{\prime}} < \sqrt{s}$, it will not be necessary to make a new energy run at the $Z^{\prime}$ mass in order to get most of its properties.
$Z^\prime$ boson as a new gauge boson has been proposed in many new physics models. The interactions of $Z^\prime$ coupling to fermions are detailed studied at the large hadron collider. A $Z^\prime$ with the mass of a few TeV has been excluded in some special models. The future lepton colliders will focus on the studies of Higgs physics which provide the advantage to investigate the interactions of Higgs boson with the new gauge bosons. We investigate the $Z^\prime ZH$ interaction via the process of $e^+e^- \to Z^\prime/Z \to ZH \to l^+l^- b \bar{b}$. The angular distribution of the final lep…
We show that the U(1)-prime models linked with the seesaw mechanism at TeV scale can lead to a successful baryogenesis through soft leptogenesis with a resonant behavior in the B parameter. Such a consideration constrains the Z-prime mass to be larger than 2-3 TeV depending on the seesaw scale and the spharelon rate. Together with multi-TeV Z-prime, large sneutrino-antisneutrino mixing and CP violating phenomena required by TeV leptogenesis could be searched for in future colliders by observing the distinct same-sign dilepton--dichargino as well as dislepton--diHiggs signatures.
The minimal $U(1)_X$ extension of the Standard Model (SM) is a well-motivated new physics scenario, where anomaly cancellation dictates new neutral gauge boson ($Z^\prime$) couplings with the SM fermions in terms of the $U(1)_X$ charges of the new scalar fields. We investigate the SM charged fermion pair-production process for different values of these $U(1)_X$ charges at future $e^-e^+$ colliders: $e^+e^-\to f\bar f$. Apart from the standard $γ$ and $Z$-mediated processes, this model features additional $s$-channel (or both $s$ and $t$-channel when $f=e^-$) $Z^\prime$ exchange which interfere…
I update the predicted leading order and next-to-leading order cross sections and total widths for W^\prime bosons that decay to top and bottom quarks at 14 TeV and 33 TeV pp colliders (pp -> W^\prime -> tb). Separate tables are included for right- and left-handed bosons. Theoretical uncertainties are completely dominated by parton distribution function uncertainties, and are computed for W^\prime_+- production at a 14 TeV pp collider.
We show that the associated production $pp\to W^{\prime}W$, and the rare decay $pp\to W'\to \bar\ell\ell W$ are useful tests of $W'$ couplings to fermions at future hadron colliders. For $M_{W'}\sim (1 - 3)$ TeV they would allow a clean determination on whether the $W'$ couples to $V-A$ or $V+A$ currents. As an illustration a model in which the $W^{\prime\pm}$ couples only to $V-A$ currents is contrasted to the left-right symmetric models which involve $V+A$ currents.
We analyse supersymmetric models augmented by an extra $U(1)$ gauge group. To avoid anomalies in these models without introducing exotics, we allow for family-dependent $U(1)^\prime$ charges, and choose a simple form for these, dependent on one $U(1)^\prime$ charge parameter only. With this choice, $Z^\prime$ decays into di-taus but not di-leptons, weakening considerably the constraints on its mass. In the supersymmetric sector, the effect is to lower the singlino mass, allowing it to be the dark matter candidate. We investigate the dark matter constraints and collider implications of such mod…
We investigate the potentials of high energy lepton-proton colliders to detect a flavor changing $l-l^{\prime}-Z$ or $l-l^{\prime}-γ$ couplings from the processes $ep\toμ(τ)X$ and $μp\to τX$. For the $l-l^{\prime}-Z$ coupling we consider string inspired $E_6$ model whereas $l-l^{\prime}-γ$ coupling is analyzed in the framework of anomalous magnetic moment type interaction (AMMI) model.
We propose a way to differentiate between various extra $U(1)$ models using flavor tagging in the decay modes $Z^{\prime}\rightarrow q{\bar{q}}$ once the extra $Z^{\prime}$ is observed at future colliders in the lepton channel. A generalization of the R parameter, namely, one for charge $\frac{1}{3}$ and one for charge $\frac{2}{3}$ quark gives a two parameter test for the various models. Flavor tagging eliminates the uncertainty because of extra fermions and can reduce the QCD background at SSC/LHC dramatically. For $E_{6}$ and $SO(10)$ based models the former is always 3. This seems to be a …
Recently a gauged two Higgs doublet model, in which the two Higgs doublets are embedded into the fundamental representation of an extra local $SU(2)_H$ group, is constructed. Both the new gauge bosons $Z^\prime$ and $W^{\prime (p,m)}$ are electrically neutral. While $Z^\prime$ can be singly produced at colliders, $W^{\prime (p,m)}$, which is heavier, must be pair produced. We explore the constraints of $Z^\prime$ using the current Drell-Yan type data from the Large Hadron Collider. Anticipating optimistically that $Z^\prime$ can be discovered via the clean Drell-Yan type signals at high lumino…
Many models, such as topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models, predict the existence of extra U(1) gauge bosons $Z^{\prime}$, which couple preferentially to the third generation. The lepton flavor violating (LFV) signals of these new particles at the future $e^{+}e^{-}$ colliders (LCs) are discussed via calculating its contributions to the LFV process $e^{+}e^{-}\toμτ$. We calculate the cross section of this process and discuss its dependence on the beam polarization. The ratio of signal over square root of the background $(S/\sqrt{B})$ is also calculated. The…
A gauged U$(1)$ extension of the Standard Model (SM) is a simple and anomaly free framework where three generations of Majorana type right-handed neutrinos (RHNs) are introduced to generate light neutrino mass and flavor mixings through the seesaw mechanism. We investigate such models at different hadron and lepton colliders via $Z^\prime$ induced Majorana type RHNs pair production. We derive bounds on U$(1)$ gauge coupling $(g^\prime)$ comparing the model cross sections with experimentally observed data for different $Z^\prime$ mass $(M_{Z^\prime})$ and RHNs mass $(M_N)$. Using these limits w…
We study $Z'$ phenomenology at hadron colliders in an $U(1)'$ extended MSSM. We choose a $U(1)'$ model with a secluded sector, where the tension between the electroweak scale and developing a large enough mass for $Z'$ is resolved by incorporating three additional singlet superfields into the model. We perform a detailed analysis of the production, followed by decays, including into supersymmetric particles, of a $Z'$ boson with mass between 4 and 5.2 TeV, with particular emphasis on its possible discovery. We select three different scenarios consistent with the latest available experimental d…
We investigate the minimal $U(1)_{L_μ-L_τ}$ model with extra heavy vector-like leptons or charged scalars. By studying the kinetic mixing between $U(1)_{L_μ-L_τ}$ gauge boson $Z^\prime$ and standard model photon, which is absent at tree level and will arise at one loop level due to $μ$, $τ$ and new heavy charged leptons or scalars, the interesting behavior is shown. It can provide possibility for visible signatures of new heavy particles. We propose to search for $Z^\prime$ at electron collider experiments, such as Belle II, BESIII and future Super Tau Charm Factory (STCF), using the monophoto…
In this work, we derive lower mass bounds on the Z' gauge boson based on the dilepton data from LHC with 13 TeV of center-of-mass energy, and forecast the sensitivity of the High-Luminosity-LHC with $L=3000 fb^{-1}$, the High-Energy LHC with $\sqrt{s}=27$ TeV, and also at the Future Circular Collider with $\sqrt{s}=100$ TeV. We take into account the presence of exotic and invisible decays of the Z' gauge boson to find a more conservative and robust limit, different from previous studies. We investigate the impact of these new decays channels for several benchmark models in the scope of two dif…
Recent measurements in $B \to K^{(*)} μ^+ μ^-$ decays are somewhat discrepant with Standard Model predictions. They may be harbingers of new physics at an energy scale potentially accessible to direct discovery. We estimate the sensitivity of future hadron colliders to the possible new particles that may be responsible for the anomalies: leptoquarks or $Z^\prime$s. We consider luminosity upgrades for a 14 TeV LHC, a 33 TeV LHC, and a 100 TeV $pp$ collider such as the FCC-hh. Coverage of $Z^\prime$ models is excellent: for narrow particles, with perturbative couplings that may explain the $b$-d…
We study the experimental constraints on dark sector CP violation that enters the visible sector through a Higgs portal coupling $H^{\dagger} H Z^{\prime}_{μν} \widetilde Z^{\prime μν}$, where the $Z^{\prime}$ is from a new U(1) gauge symmetry which is assumed to couple to lepton number. We compute explicitly the leading two-loop contribution of this effective operator to the electron electric dipole moment (EDM) and show that the resulting constraints are comparable to those from direct $Z^{\prime}$ searches at electron-positron colliders when the effective operator is generated at tree level…
The recent observation of three events by the CDMS II experiment can be interpreted as a 8.6 GeV dark matter scatters elastically with the nucleons inside the silicon detectors with a spin-independent cross section of 1.9 x 10^-41 cm^2. We employ the effective dark matter interaction approach to fit to the interpreted cross section, and make predictions for monojet and monophoton production at the LHC with the fitted parameters. We show that some of the operators are already ruled out by current data while the others can be further probed in the upcoming 14 TeV run of the LHC.
In this work we study the interactions of the $Z$ and $Z^{\prime}$ generated by kinetic mixing in a class of theories for physics beyond the standard model motivated by the dark matter problem, containing a spontaneously broken extra $U(1)_{d}$ gauge factor group in a hidden scenario and a Higgs sector respecting custodial symmetry. It is shown that custodial symmetry allows us to write the $Z$ and $Z^{\prime}$ couplings to standard model fermions in terms of the measured values of $α$, $G_{F}$, $M_{Z}$ and $M_{Z^{\prime}}$. Working at the loop level, we calculate the ratio $ρ_{0}=M^{2}_{W}/\h…
With null results in resonance searches at the LHC, the physics potential focus is now shifting towards the interpretation of non-resonant phenomena. An example of such shift is the increased popularity of the EFT programme. We can embark on such programme owing to good integrated luminosity and an excellent understanding of the detectors, which will allow these searches to become more intense as the LHC continues. In this paper we provide a framework to perform this interpretation in terms of a diverse set of scenarios, including {\it 1.) } generic heavy new physics described at low energies …
Hadronic production of nonrelativistic boundstates of $b^{\prime}$ or isosinglet quarks D with suppressed weak decays is investigated for LHC and SSC energies. QCD corrections to production and decay rates are incorporated. Large rates for final states from $η_{b^{\prime}}\rightarrow HZ$ are predicted.
The pair productions of leptons and quarks at $e^+e^-$ Higgs factory are an important probe for new physics via precise measurements. The discovery and exclusion limits of $Z^\prime$ models at the International Linear Collider with $\sqrt{s} = 250$, 500 and 1000 GeV are calculated with selection efficiencies estimated in the existing full simulation studies. It shows a large potential of BSM searches with precise measurements at future energy-frontier $e^+e^-$ colliders.
In scenarios beyond the Standard Model (BSM) characterized by charged ($W^\prime$) or neutral ($Z^\prime$) massive gauge bosons with large width, resonant mass searches are not very effective, so that one has to exploit the tails of the mass distributions measured at the Large Hadron Collider (LHC). In this case, the LHC sensitivity to new physics signals is influenced significantly by systematic uncertainties associated with the Parton Distribution Functions (PDF), particularly in the valence quark sector relevant for the multi-TeV mass region. As a BSM framework featuring such conditions, we…
The sensitivity to the $Z^\prime$ couplings of the processes $e^+e^-\to l^+l^-,\bar{b}b$ and $\bar{c}c$ at the linear collider with $\sqrt{s}=500 GeV$ with initial beam polarization, for typical extended model examples are studied. To this aim, the suitable integrated, polarized, observables directly related to the helicity cross sections that carry information on the individual $Z^\prime$ chiral couplings to fermions are used. We discuss the derivation of separate, model-independent limits on the couplings in the case of no observed indirect $Z^\prime$ signal within the expected experimental …
We consider a class of gauged $U(1)$ extensions of the Standard Model (SM), where the light neutrino masses are generated by an inverse seesaw mechanism. In addition to the three right handed neutrinos, we add three singlet fermions and demand an extra $Z_2$ symmetry under which, the third generations of both of the neutral fermions are odd, which in turn gives us a stable dark matter candidate. We express the $U(1)$ charges of all the fermions in terms of the U(1) charges of the standard model Higgs and the new complex scalar. We study the bounds on the parameters of the model from vacuum sta…
Within the framework of nonrelativistic QCD, we make a detailed discussion on the doubly heavy baryon production through the $e^+ e^-$ annihilation channel, $e^{+}e^{-}\rightarrowγ/Z^0 \rightarrow Ξ_{QQ^{\prime}} +\bar{Q} +\bar{Q^{\prime}}$, at a high luminosity $e^{+}e^{-}$ collider. Here $Q^{(\prime)}$ stands for the heavy $b$ or $c$ quark. In addition to the channel through the usually considered diquark state $(QQ^{\prime})[^3S_1]_{\bf\bar{3}}$, contributions from the channels through other same important diquark states such as $(QQ^{\prime})[^1S_0]_{\bf 6}$ have also been discussed. Uncer…
We introduce a light dark photon $A_μ^\prime$ to the minimal Higgs portal model, by coupling the Higgs boson to "dark QED" containing fermionic dark matter, which gives rise to rich and interesting collider phenomenology. There are two prominent features in such a simple extension -- the Higgs boson could have decays into the long-lived dark photon through the "mono-$A^\prime$ channel," or into multiple collimated leptons via "darkonium," depending on the mixing parameter of the $A_μ^\prime$ with the visible photon. We initiate a study on the possibility of probing the parameter space of the m…
We analyze the collider signatures of models with a vector-like top-prime quark and a massive color-octet boson. The top-prime quark mixes with the top quark in the Standard Model, leading to richer final states than ones that are investigated by experimental collaborations. We discuss the multi-lepton final states, and show that they can provide increased sensitivity to models with a top-prime quark and gluon-prime. Searches for new physics in high multiplicity events are an important component of the LHC program and complementary to analyses that have been performed.
The doubly heavy baryon $Ξ_{QQ^{\prime}}$ ($Q^{(\prime)}$ = $b$ or $c$) is different from the ordinary baryons. The production of the doubly heavy baryon can provide valuable insight on how the colored $(QQ^{\prime})$-diquark can be transformed into the color-singlet baryon. As a sequential work of Ref.[2], we make a further study on the doubly heavy baryon production through the $e^+ e^-$ annihilation channel, $e^{+} + e^{-}\rightarrowγ/Z^0 \rightarrow Ξ_{QQ^{\prime}} +\bar{Q} +\bar{Q^{\prime}}$, within the nonrelativistic QCD framework. In addition to the total cross sections, we present the…
Unlike QED, since F_{μν}^a(x)F^{μνa}(0) in QCD contains cubic and quartic powers of the gluon field the present definition of the gluon distribution function at high energy colliders is not consistent with the number operator interpretation of the gluon. In this paper we derive the correct definition of the gluon distribution function at high energy colliders from first principles which is consistent with the number operator interpretation of the gluon and is gauge invariant and is consistent with the factorization theorem in QCD.
Baryon and lepton numbers being accidental global symmetries of the Standard Model (SM), it is natural to promote them to local symmetries. However, to preserve anomaly freedom, only combinations of B-L are viable. In this spirit, we investigate possible dark matter realizations in the context of the $U(1)_{B-L}$ model: (i) Dirac fermion with unbroken B-L; (ii) Dirac fermion with broken B-L; (iii) scalar dark matter; (iv) two component dark matter. We compute the relic abundance, direct and indirect detection observables and confront them with recent results from Planck, LUX-2016, and Fermi-LA…
Our aim is to establish some signatures of the extra gauge boson ${Z^\prime}$, predicted in two versions of ${SU (3)_C \times SU (3)_L \times U (1)_X}$ model and to show possible differences between these signatures. First, by considering the process $e^+ + e^- \longrightarrow μ^+ +μ^- $, we obtain some observables and next, by considering additional hadronic final states, we obtain lower bounds for $M_{Z^\prime}$, within 95% C.L.. We also include our preliminary results concerning $p \bar p$ and $p p$ collisions in order to support our conclusions about the possibility to discriminate the var…
We study the collider signatures of a T-odd gauge boson $W_{H}$ pair production in the Littlest Higgs Model with T-parity (LHT) at Large Hadron Collider (LHC) and Linear Collider (LC). At the LHC, we search for the $W_{H}$ boson using its leptonic decay, i.e. $pp\to W_{H}^{+}W_{H}^{-}\to A_{H}A_{H}\ell^{+}ν_{\ell}\ell^{\prime-}\barν_{\ell^{\prime}}$, which gives rise to a collider signature of $\ell^{+}\ell^{\prime-}+\met$. We demonstrate that the LHC not only has a great potential of discovering the $W_{H}$ boson in this channel, but also can probe enormous parameter space of the LHT. Due to …
We study the production of gauge boson pairs at the next generation of linear $e^+e^-$ colliders operating in the $eγ$ mode. The processes $eγ\rightarrow VV^\prime F$ ($V,V^\prime =W$, $Z$, or $γ$ and $F=e$ or $ν$) can give valuable information on possible deviations of the quartic vector boson couplings from the Standard Model predictions. We establish the range of the new couplings that can be explored in these colliders based on a $3σ$ effect in the total cross section. We also present several kinematical distributions of the final state particles that could manifest the underlying new dyna…
Dark sector may couple to the Standard Model via one or more mediator particles. We discuss two types of mediators: the dark photon $A^{\prime}$ and the dark scalar mediator $ϕ$. The total cross-sections and various differential distributions of the processes $e^{+} e^{-} \rightarrow q \bar{q} A^{\prime}$ and $e^{+} e^{-} \rightarrow q \bar{q} ϕ$ ($q=u,~d,~c,~s$ and $b$ quarks) are discussed. We focus on the study of the invisible $A^{\prime}$ due to the cleaner background at future $e^{+} e^{-}$ colliders. It is found that the kinematic distributions of the two-jet system could be used to ide…
We study impacts of dimension-five lepton-number violating operators associated with two same-sign weak bosons, $\ell^\pm \ell^{\prime \pm} W^\mp W^\mp$, on current and future experiments for neutrino oscillation, lepton-number violating rare processes and high-energy collider experiments. These operators can contain important information on the origin of tiny neutrino masses, which is independent of that from the so-called Weinberg operator. We examine constraints on the coefficients of the operators by the neutrino oscillation data. Upper bounds on the coefficients are also investigated by u…
Three neutral resonances $Ξ_c(2923)^0$, $Ξ_c(2939)^0$ and $Ξ_c(2965)^0$ have been observed in the $Λ_c^+ K^-$ mass spectrum by the LHCb Collaboration. Given the $Ξ_c$ and $Ξ_c^\prime$ mass spectra predicted by the constituent quark models, these three resonances are tentatively treated as the $λ-$mode $Ξ_c(2S)$, $Ξ_c^\prime(2S)$, $Ξ_c^{\prime *}(2S)$, and $Ξ_c^\prime(1P)$ states, and their strong decay behaviors are calculated within the $^3P_0$ model. Our results indicate that the $Ξ_c(2923)^0$ and $Ξ_c(2939)^0$ can be clarified into the $J^P=3/2^-$ and $5/2^-$ $Ξ_c^\prime(1P)$ states respect…
We study the effects of vector-like leptons on the $W$ boson mass in a model with a vector-like $U(1)^\prime$ gauge symmetry. This model provides simultaneous explanations for the recent anomalies in the muon anomalous magnetic moment and the semi-leptonic decays of $B$ mesons. We found that the recent result of the $W$ boson mass precise measurement at CDF can be explained if the charged (neutral) vector-like lepton is lighter than 250 (80) GeV. The light vector-like leptons may not be excluded by collider experiments if these decay to a physical mode of the $U(1)^\prime$ breaking scalar fiel…
Thanks to the recent careful revisit of the theoretical prediction of the $B_c$ meson lifetime, the conservative upper bound on the branching ratio (BR) of $τν$ mode is found to be $\simeq 63\%$ due to the large charm quark mass uncertainty. Although it is well known that a charged Higgs ($H^-$) interpretation of the $R_{D^{(*)}}$ anomaly is excluded by the previously proposed bounds, BR$(B_c\toτν)\le 30\%$ and $\le10\%$, $H^-$ can still explain the anomaly within $1σ$ if we adopt the 63$\%$ one. The scalar contribution is also favored by the polarization data $F_L^{D^*}$ measured at the Belle…
The top quark forward-backward asymmetry measured at the Tevatron collider shows a large deviation from standard model expectations. Among possible interpretations, a non-universal $Z^\prime$ model is of particular interest as it naturally predicts a top quark in the forward region of large rapidity. To reproduce the size of the asymmetry, the couplings of the $Z^\prime$ to standard model quarks must be large, inevitably leading to copious production of same-sign top quark pairs at the energies of the Large Hadron Collider (LHC). We explore the discovery potential for $tt$ and $ttj$ production…
A coupling of a dark photon $A'$ from a $U(1)_{A'}$ with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter $ε$. A non-zero $ε$ also induces a mixing between $A'$ and $Z$ if dark photon mass $m_{A'}$ is not zero. This mixing can be large when $m_{A'}$ is close to $m_Z$ even if the parameter $ε$ is small. Many efforts have been made to constrain the parameter $ε$ for a low dark photon mass $m_{A'}$ compared with the $Z$ boson mass $m_Z$. We study the search for dark photon in $e^+e^- \to γA' \to γμ^+ μ^-$ for a dark photon mass $m_{A'}$ as large…
