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Register a new userMeasuring the Higgs Boson Self-coupling at High Energy e^+e^- Colliders
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U. Baur
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Standard Model Higgs pair production at e^+e^- colliders has the capability to determine the Higgs boson self-coupling lambda. I present a detailed analysis of the e^+e^- -> ZHH and e^+e^- -> ubar u HH signal channels, and the relevant background processes, for future e^+e^- linear colliders with center of mass energies of sqrt{s}=0.5 TeV, 1 TeV, and 3 TeV. Special attention is given to the role non-resonant Feynman diagrams play, and the theoretical uncertainties of signal and background cross sections. I also derive quantitative sensitivity limits for lambda. I find that an e^+e^- collider with sqrt{s}=0.5 TeV can place meaningful bounds on lambda only if the Higgs boson mass is relatively close to its current lower limit. At an e^+e^- collider with sqrt{s}=1 TeV (3 TeV), lambda can be determined with a precision of 20-80% (10-20%) for integrated luminosities in the few ab^{-1} range and Higgs boson masses in the range m_H=120-180 GeV.
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We analyzed the triple Higgs boson self-coupling at future $e^{+}e^{-}$ colliders energies, with the reactions $e^{+}e^{-}to b bar b HH, t bar t HH$. We evaluate the total cross-sections for both $bbar bHH$ and $tbar tHH$, and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. We vary the triple coupling $kappalambda_{3H}$ within the range $kappa=-1$ and +2. The numerical computation is done for the energies expected to be available at a possible Future Linear $e^{+}e^{-}$ Collider with a center-of-mass energy $800, 1000, 1500$ $GeV$ and a luminosity 1000 $fb^{-1}$. Our analysis is also extended to a center-of-mass energy 3 $TeV$ and luminosities of 1000 $fb^{-1}$ and 5000 $fb^{-1}$. We found that for the process $e^{+}e^{-}to b bar b HH$, the complete calculation differs only by 3% from the approximate calculation $e^{+}e^{-}to ZHH(Zto bbar b)$, while for the process $e^{+}e^{-}to t bar tHH$, the expected number of events, considering the decay products of both $t$ and $H$, is not enough to obtain an accurate determination of the triple Higgs boson self-coupling.
We analyse the loop induced production of Higgs boson pairs at future high--energy $e^+e^-$ colliders, both in the Standard Model and in its minimal supersymmetric extension. The cross sections for Standard Model Higgs pair production through $W/Z$ boson loops, $ee ra H^0 H^0$, are rather small but the process could be visible for high enough luminosities, especially if longitudinal polarization is made available. In the Minimal Supersymmetric Standard Model, the corresponding processes of CP--even or CP--odd Higgs boson pair production, $ee ra hh, HH, Hh$ and $ee ra AA$ have smaller cross sections, in general. The additional contributions from chargino/neutralino and slepton loops are at the level of a few percent in most of the supersymmetric parameter space.
We study the double Higgs boson production processes $e^+e^- to hh fbar{f}$ ($f eq t$) with $h$ being the 125 GeV Higgs boson in the two-Higgs-doublet model with a softly-broken $Z_2$ symmetry. The cross section can be significantly enhanced, typically a few hundreds percent, as compared to the standard model prediction due to resonant effects of heavy neutral Higgs bosons, which becomes important in the case without the alignment limit. We find a strong correlation between the enhancement factor of the cross section and the scaling factor of the $hfbar{f}$ couplings under constraints from perturbative unitarity, vacuum stability and current experimental data at the LHC as well as the electroweak precision data.
Since the discovery of the Higgs boson at the Large Hadron Collider, a future electron-position collider has been proposed for precisely studying its properties. We investigate the production of the Higgs boson at such an $e^+e^-$ collider associated with a $Z$ boson, and calculate for the first time the mixed QCD-electroweak corrections to the total cross sections. We provide an approximate analytic formula for the cross section and show that it reproduces the exact numeric results rather well for collider energies up to 350 GeV. We also provide numeric results for $sqrt{s}=500$ GeV, where the approximate formula is no longer valid. We find that the $mathcal{O}(alphaalpha_s)$ corrections amount to a 1.3% increase of the cross section for a center-of-mass energy around 240 GeV. This is significantly larger than the expected experimental accuracy and has to be included for extracting the properties of the Higgs boson from the measurements of the cross sections in the future.
We study the triple Higgs self-coupling at future $e^{+}e^{-}$ colliders energies, with the reactions $e^{+}e^{-}to b bar b HH$ and $e^{+}e^{-}to t bar t HH$. We evaluate the total cross section of $bbar bHH$, $tbar tHH$ and calculate the total number of events considering the complete set of Feynman diagrams at tree-level. The sensitivity of the triple Higgs coupling is considered in the Higgs mass range 110-190 $GeV$, for the energy which is expected to be available at a possible Next Linear $e^{+}e^{-}$ Collider with a center-of-mass energy $800, 1000, 1500$ $GeV$ and luminosity 1000 $fb^{-1}$.
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