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Register a new userOn a $Z^{prime}$ signature at next high energy electron-positron colliders
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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.
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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.
In recent years there have been many proposals for new electron-positron colliders, such as the Circular Electron-Positron Collider, the International Linear Collider, and the Future Circular Collider in electron-positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the $h,Z$ threshold. However, there are proposals to run these colliders at the lower $WW$ threshold and $Z$-pole energies. In this paper, we propose a new search for Higgs physics accessible at lower energies: $e^+e^-rightarrow h,Z_d$, where $Z_d$ is a new light gauge boson such as a dark photon or dark-$Z$. Such searches can be conducted at the $WW$ threshold, i.e. energies below the $h,Z$ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron-positron colliders, these searches will be sensitive to $Z_d$ masses below 1 GeV, which is lower than the current direct LHC searches. We will show that at $sqrt{s}=160$ GeV with 10 ab$^{-1}$, a search for $e^+e^-rightarrow h,Z_d$ is sensitive to $h-Z-Z_d$ couplings of $deltasim 8times 10^{-3}$ and cross sections of $sim 1-2$ ab for $Z_d$ masses below 1 GeV. The results are similar at $sqrt{s}=240$ GeV with 5 ab$^{-1}$.
The review of using of compton backscattering method for determination of the beam energy in collider experiments is given.
An electron-positron linear collider in the energy range between 500 and 1000 GeV is of crucial importance to precisely test the Standard Model and to explore the physics beyond it. The physics program is complementary to that of the Large Hadron Collider. Some of the main physics goals and the expected accuracies of the anticipated measurements at such a linear collider are discussed. A short review of the different collider designs presently under study is given including possible upgrade paths to the multi-TeV region. Finally a framework is presented within which the realisation of such a project could be achieved as a global international project.
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.
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