Radiative decays of the Higgs boson to a pair of fermions

Abstract

Abstract:We revisit the radiative decays of the Higgs boson to a fermion pair h → ff γ where f denotes a fermion in the Standard Model (SM). We include the chiralityflipping diagrams via the Yukawa couplings at the order O(y 2 f α), the chirality-conserving contributions via the top-quark loops of the order O(y 2 t α 3 ), and the electroweak loops at the order O(α 4 ). The QED correction is about Q 2 f × O(1%) and contributes to the running of fermion masses at a similar level, which should be taken into account for future precision Higgs physics. The chirality-conserving electroweak-loop processes are interesting from the observational point of view. First, the branching fraction of the radiative decay h → µ + µ − γ is about a half of that of h → µ + µ − , and that of h → e + e − γ is more than four orders of magnitude larger than that of h → e + e − , both of which reach about 10 −4 . The branching fraction of h → τ + τ − γ is of the order 10 −3 . All the leptonic radiative decays are potentially observable at the LHC Run 2 or the HL-LHC. The kinematic distributions for the photon energy or the fermion pair invariant mass provide non-ambiguous discrimination for the underlying mechanisms of the Higgs radiative decay. We also study the process h → ccγ and evaluate the observability at the LHC. We find it potentially comparable to the other related studies and better than the h → J/ψ γ channel in constraining the charm-Yukawa coupling.

Higgs decays to two leptons and a photon beyond leading order in the SMEFT

“…Furthermore we apply a cut on the angle between the photon and each of the leptons requiring cos θ > 0.8. This is different from the approach in [11],…”

“…, (11) where Θ denotes the unit step function, the superscript "(0)" indicates this is the tree level result, and G = 0 defines the boundary of integration and is given by [37]:…”

“…The coupling of the Higgs boson to two photons or a Z-boson and photon in the Standard Model (SM) were developed in [1][2][3]. The decay H → ¯ γ in the SM has more recently been considered in [4][5][6][7][8][9][10][11][12]. In the case of the decay H → Zγ the narrow width approximation is typically employed for the Z boson.…”

Charm-quark Yukawa coupling in h→cc¯γ at LHC

“…In principle, one-loop electroweak processes also contribute to h → ccγ, as discussed in[37]. However, it can be safely neglected given the hypothetically large Yukawa coupling yc accessible here and the absence of interference between the QED radiation and EW contributions.…”

“…It has been recently pointed out that the radiative decay of the Higgs boson to a pair of charm quarks could be used to constrain the charm-quark Yukawa coupling with the final state h → ccγ [37]. The addition of the photon can be helpful for triggering as well as suppressing both non-Higgs and Higgs backgrounds.…”