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Register a new userTests of Quantum Chromo Dynamics at e^+e^- Colliders
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Stefan Kluth
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The current status of tests of the theory of strong interactions, Quantum Chromo Dynamics (QCD), with data from hadron production in e^+e^- annihilation experiments is reviewed. The LEP experiments ALEPH, DELPHI, L3 and OPAL have published many analyses with data recorded on the Z^0 resonance at sqrt(s)=91.2 GeV and above up to sqrt(s)>200 GeV. There are also results from SLD at sqrt(s)=91.2 GeV and from reanalysis of data recorded by the JADE experiment at 14<sqrt(s)<44 GeV. The results of studies of jet and event shape observables, of particle production and of quark gluon jet differences are compared with predictions by perturbative QCD calculations. Determinations of the strong coupling constant alpha_S(M_Z) from jet and event shape observables, scaling violation and fragmentation functions, inclusive observables from Z^0 decays, hadronic tau decays and hadron production in low energy e^+e^- annihilation are discussed. Updates of the measurements are performed where new data or improved calculations have become available. Finally, investigations of the gauge structure of QCD are summarised.
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A short review of the history and a slide-show of QCD tests in $e^+e^-$ annihilation is given. The world summary of measurements of $alpha_s$ is updated.
In this note, I will review the opportunities offered by the hint of a new resonance observed at LHC for future e+e- TeV linear collider (LC) projects. This discussion is mainly influenced by two specific scenarios of physics which assume either a (pseudo-)scalar or a tensor resonance, but these estimates can be used in most scenarios. I envisage either a photon collider, which has a guaranteed signal with the LHC observation, or a standard e+e- collider, more straightforward to implement. After a detailed study of the heavy graviton scenario, I conclude that at a TeV LC, high accuracy measurements, including rare modes, allow to unambiguously establish the origin of this resonance. Also envisaged in some detail is a radion scenario which illustrates the production of a scalar. The role of an LC for precision measurements on Higgs and top couplings is recalled in the context of the Randall Sundrum model.
This paper intends to collect available data on searches for scalar resonances at LHC. It is suggested that, in the absence of SUSY, the most compelling picture is the composite framework, with the idea that the lightest particles are composite scalars of the pseudo-Nambu-Goldstone type, emerging from a broken symmetry at a higher scale, the h(125) boson being one of them. Searches in two-photons, Z-photon, ZZ into 4 leptons, top, h and W pairs are reviewed. A recent search based on lepton tagging from a spectator W/Z is also discussed. Aside from the already well-known scalar observed by CMS and LEP2 at 96 GeV, I discuss the evidence and the interpretation for a possible resonance observed in ZZ around 700 GeV by CMS and ATLAS and some evidence for a CP-odd scalar at ~400 GeV. Future searches at HL-LHC and at $e^+e^-$ colliders are briefly sketched.
In gauge-Higgs unification the 4D Higgs boson appears as a part of the fifth dimensional component of gauge potentials, namely as a fluctuation mode of the Aharonov-Bohm phase in the extra dimension. The $SO(5) times U(1) times SU(3)$ gauge-Higgs unification gives nearly the same phenomenology as the standard model (SM) at low energies. It predicts KK excited states of photon, $Z $ boson, and $Z_R$ boson ($Z$ bosons) around 7 - 8 TeV. Quarks and leptons couple to these $Z$ bosons with large parity violation, which leads to distinct interference effects in $e^+ e^- rightarrow mu^+ mu^-, q , bar q$ processes. At 250 GeV ILC with polarized electron beams, deviation from SM can be seen at the 3 - 5 sigma level even with 250 fb$^{-1}$ data, namely in the early stage of ILC. Signals become stronger at higher energies. Precision measurements of interference effects at electron-positron colliders at energies above 250 GeV become very important to explore physics beyond the standard model.
In this work, we consider the process $e^{+}+e^{-}rightarrow bbar{b}+slashed{E}_{T}$, at the future electron-positron colliders such as the International Linear Collider and Compact Linear Collider, to look for the dark matter (DM) effect and identify its nature at two different center-of-mass energies $E_{c.m.}=500~mathrm{GeV}~and~1~mathrm{TeV}$. For this purpose, we take two extensions of the standard model, in which the DM could be a real scalar or a heavy right-handed neutrino (RHN) similar to many models motivated by neutrino mass. In the latter extension, the charged leptons are coupled to the RHNs via a lepton flavor violating interaction that involves a charged singlet scalar. After discussing different constraints, we define a set of kinematical cuts that suppress the background, and generate different distributions that are useful in identifying the DM nature. The use of polarized beams (like the polarization $P(e^{-},e^{+})=left[+0.8,-0.3right]$ at the International Linear Collider) makes the signal detection easier and the DM identification more clear, where the statistical significance gets enhanced by twice (five times) for scalar (RHN) DM.
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