No Arabic abstract
We study the process $e^-e^+to gamma H$, where $H$ represents $H_{SM}$, $h^0$ or $H^0$, which occurs at the one loop level in the standard model (SM) or in the minimal supersymmetric standard model (MSSM). We establish supersimple (sim) high energy expressions for all helicity amplitudes of this process, and we identify their level of accuracy for describing the various polarized and unpolarized observables, and for distinguishing SM from MSSM or another beyond the standard model (BSM). We pay a special attention to transverse electron-positron polarizations and azimuthal dependencies induced by the imaginary parts of the amplitudes, which are relatively important in this process.
We study the process $e^-e^+to ZH$ where $H$ represents the standard model (SM) Higgs particle $H_{SM}$, or the MSSM ones $h^0$ and $H^0$. In each case, we compute the one-loop effects and establish very simple expressions, called supersimple (sim), for the helicity conserving (dominant) and the helicity violating (suppressed) amplitudes. Such expressions, are then used to construct various cross sections and asymmetries, involving polarized or unpolarized beams and Z-polarization measurements. We examine the adequacy of such expressions to distinguish SM or MSSM effects, from other types of BSM (beyond the standard model) contributions.
A precise measurement of the Higgs $h to Z gamma$ decay is very challenging at the LHC, due to the very low %SM $h to Z gamma, (Z to ell ell)$ branching fraction and the shortage of kinematic handles to suppress the large SM $Z gamma$ background. We show how such a measurement would be significantly improved by considering Higgs production in association with a hard jet. We compare the prospective HL-LHC sensitivity in this channel with other Higgs production modes where $h$ is fairly boosted, e.g.~weak boson fusion, and also to the potential $h to Z gamma$ measurement achievable with a future $e^{+}e^{-}$ circular collider ({sl fcc-ee}). Finally, we discuss new physics implications of a precision measurement of $h to Z gamma$.
Absorption of high-energy $bar{ u}_e$ over electrons above the W boson production threshold is reexamined. It is pointed out that, in the case of photon emissions along the direction of incident high-energy $bar{ u}_e$, the kinematically allowed average energy carried by the final state hard photon can be $leq 1%$ of the incident $bar{ u}_e$ energy above the W boson production threshold. The differential energy spectrum for the final state hard photon is calculated. We also discuss implications of our results for the prospective search of high-energy $bar{ u}_e$ through this final state hard photon.
The 1-loop effects of the MSSM at the ILC are investigated through numerical analysis. We studied the higgs production processes $e^-e^+rightarrow Zh$ and $e^-e^+rightarrow ubar{ u}h$ at the ILC. It is found that the magnitude of the MSSM contribution through the 1-loop effects is sizable enough to be detected. In the study, three sets of the MSSM parameters are proposed, which are consistent with the observed higgs mass, the muon $g$-$2$, the dark matter abundance and the decay branching ratios of $B$ mesons. In the $e^-e^+rightarrow Zh$ process, the 1-loop effects of the MSSM are visible and the distinction of the parameter sets is partially possible. For the study of $e^-e^+rightarrow ubar{ u}h$, we used the equivalent $it W$-boson approximation in the evaluation of the 1-loop cross section. While the 1-loop effect of the MSSM is visible, the distinction of the parameter sets might not be possible in this process under the value of realistic luminosity at the ILC.
Results of the SND experiment at the VEPP-2M e+ e- collider on the QED processes e+ e- --> e+ e- gamma and e+ e- --> e+ e- gamma gamma with production at large angles are presented. Energy and angular distributions of the final particles were studied. No deviations from QED with an accuracy of 3.8% for the first process and 10.3% for the second were found.