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Register a new userHiggs decay into a lepton pair and a photon revisited
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Ivan Ni\\v{s}and\\v{z}i\\'c
Publication date
2020
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English
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We present new calculations of the differential decay rates for $Hto ell^+ell^- gamma$ with $ell=e$ or $mu$ in the Standard Model. The branching fractions and forward-backward asymmetries, defined in terms of the flight direction of the photon relative to the lepton momenta, depend on the cuts on energies and invariant masses of the final state particles. For typical choices of these cuts we find the branching ratios $B(Hto e bar e gamma)=5.8cdot 10^{-5}$ and $B(Hto mu bar mu gamma)=6.4cdot 10^{-5}$ and the forward-backward asymmetries $mathcal{A}^{(e)}_{text{FB}}=0.343$ and $mathcal{A}^{(mu)}_{text{FB}}=0.255$. We provide compact analytic expressions for the differential decay rates for the use in experimental analyses.
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The decay $Hto ell^+ell^- gamma$, $ell=e,mu$, receives contributions from $Hto Z[to ell^+ell^-] gamma$ and a non-resonant contribution, both of which are loop-induced. We describe how one can separate these sub-processes in a gauge-independent way, define the decay rate $Gamma(Hto Zgamma)$, and extract the latter from differential $Hto ell^+ell^- gamma$ branching ratios. For $ell=mu$ also the tree decay rate, which is driven by the muon Yukawa coupling, is important. We propose kinematic cuts optimized to separate the three contributions, paving the way to the milestones (i) discovery of $Hto Z gamma$, (ii) discovery of $Hto mu^+mu^- left. gammaright|_{rm tree}$, and (iii) quantification of new physics in both the effective $H$-$Z$-$gamma$ and non-resonant $H$-$ell^+$-$ell^-$-$gamma$ couplings.
The Higgs-boson decay h -> gamma l+ l- for various lepton states l = (e, mu, tau) is analyzed. The differential decay width and forward-backward asymmetry are calculated as functions of the dilepton invariant mass in a model where the Higgs boson interacts with leptons and quarks via a mixture of scalar and pseudoscalar couplings. These couplings are partly constrained from data on the decays to leptons, h -> l+ l-, and quarks h -> q bar{q} (where q = (c, b)), while the Higgs couplings to the top quark are chosen from the two-photon and two-gluon decay rates. Nonzero values of the forward-backward asymmetry will manifest effects of new physics in the Higgs sector. The decay width and asymmetry integrated over the dilepton invariant mass are also presented.
The production of lepton pairs in the Higgs boson decay $h to ell^+ ell^- gamma$ is studied. The emphasis is put on the structure of the Higgs boson interaction with the fermions. This interaction is chosen as a mixture of the scalar and pseudo-scalar couplings, and, in addition, it is supposed to be non-Hermitian. We study prediction of this model for the observables in the $h to ell^+ ell^- gamma$ decay for the $e^+ e^-$, $mu^+ mu^-$ and $tau^+ tau^-$ pairs. The differential decay width and lepton forward-backward asymmetry are calculated as functions of the dilepton invariant mass for several sets of $h f bar{f}$ coupling constants. The influence of non-Hermitian $h f bar{f}$ interaction on the forward-backward asymmetry is studied, and large influence of a possible non-Hermiticity of the Higgs interaction with the top quarks on forward-backward asymmetry for $e^+ e^-$ and $mu^+ mu^-$ pairs is stressed.
We study the exclusive decay of $J/Psi$ into a lepton pair combined with light hadrons in the kinematic region, specified by that the total energy of the light hadrons is much smaller than $m_c$, the mass of the $c$-quark. In this region, the nonperturbaive effect related to $J/Psi$ and that related to the light hadrons can be separated, the former is represented by a NRQCD matrix element, while the later is represented by a matrix element of a correlator of electric chromofields. The results are obtained in a axial gauge by assumming that contributions from two-gluon emmssion are dominant. But we can show that these results can be obtained without the assumption in arbitrary gauges. A discussion of the results are presented.
The discovery of the Standard Model (SM) Higgs boson at the LHC completed the theory of electroweak and strong interactions. To determine the Higgs bosons intrinsic properties, more measurements on its various decay channels are still necessary. In this paper, we investigate $Hto ellbar{ell}Z$ and $Hto u_ellbar{ u}_ell Z$ (with $ell=e$, $mu$, $tau$) processes at the next-to-leading order electroweak accuracy. The total decay widths, and the differential decay rates with respect to various kinematic variables are obtained. For a typical choice of cut on the invariant mass of lepton pair, we find the branching ratios $mathcal{B}(Hto ellbar{ell}Z)=7.5times 10^{-4}$ (with $ell=e, mu$), $mathcal{B}(Hto tau^-tau^+ Z)=7.3times 10^{-4}$, and $mathcal{B}(Hto u_ellbar{ u}_ell Z)=1.5times 10^{-3}$ (with $ell=e, mu, tau$), which are attainable in the LHC experiments.
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