We show that the accumulated LEP-II data taken at $sqrt{s} =$ 130 to 206 GeV can establish more restrictive bounds on doubly charged bileptons couplings and masses than any other experiment so far. We also analyze the discovery potential of a prospective linear collider operating in both $e^+ e^-$ and $e gamma$ modes.
New heavy charged lepton production and decay signatures at future electron-positron colliders are investigated at $sqrt {s}=500$ GeV. The consequences of model dependence for vector singlets and vector doublets are studied. Distributions are calculated including hadronization effects and experimental cuts that suppress the standard model background. The final state leptonic energy distributions are shown to give a very clear signature for heavy charged leptons.
We investigate the prospects for discovering axion-like particles (ALPs) via a light-by-light (LBL) scattering at two colliders, the future circular collider (FCC-ee) and circular electron-positron collider (CEPC). The protexttt{mi}sing sensitivities to the effective ALP-photon coupling $g_{agammagamma}$ are obtained. Our numerical results show that the FCC-ee and CEPC might be more sensitive to the ALPs with mass 2 GeV $sim$ 10 GeV than the LHC and CLIC.
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 $phi$. The total cross-sections and various differential distributions of the processes $e^{+} e^{-} rightarrow q bar{q} A^{prime}$ and $e^{+} e^{-} rightarrow q bar{q} phi$ ($q=u,~d,~c,~s$ 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 identify (or exclude) the dark photon and the dark scalar mediator, as well as to distinguish between them. We further study the possibility of a search for dark photons at a future CEPC experiment with $sqrt{s}=$ 91.2 GeV and 240 GeV. With CEPC running at $sqrt{s}=$ 91.2 GeV, it would be possible to perform a decisive measurement of the dark photon (20 GeV $< m_{A^{prime}} <$ 60 GeV) in less than one operating year. The lower limits of the integrated luminosity for the significance $S/sqrt{B}=$ 2$sigma$, 3$sigma$ and 5$sigma$ are presented.
Doubly-charged Higgs bosons ($Delta^{--}/Delta^{++}$) appear in several extensions to the Standard Model and can be relatively light. We review the theoretical motivation for these states and present a study of the discovery reach in future runs of the Fermilab Tevatron for pair-produced doubly-charged Higgs bosons decaying to like-sign lepton pairs. We also comment on the discovery potential at other future colliders.
The isospin doublet scalar field with hypercharge 3/2 is introduced in some new physics models such as tiny neutrino masses. Detecting the doubly charged scalar bosons from the doublet field can be a good probe of such models. However, their collider phenomenology has not been examined sufficiently. We investigate collider signatures of the doubly and singly charged scalar bosons at the LHC for the high-luminosity upgraded option (HL-LHC) by looking at transverse mass distributions etc. With the appropriate kinematical cuts we demonstrate the background reduction in the minimal model in the following two cases depending on the mass of the scalar bosons. (1) The main decay mode of the singly charged scalar bosons is the tau lepton and missing (as well as charm and strange quarks). (2) That is into a top bottom pair. In the both cases, we assume that the doubly charged scalar boson is heavier than the singly charged ones. We conclude that the scalar doublet field with $Y = 3/2$ is expected to be detectable at the HL-LHC unless the mass is too large.
E. M. Gregores
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(2001)
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"New Limits on Doubly Charged Bileptons from CERN LEP Data and the Search at Future Electron-Positron and Electron-Photon Colliders"
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Andre Gusso
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