Abstract
We present new calculations of the differential decay rates for $H\to \ell^+\ell^- \gamma$ 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 $B(H\to e \bar e \gamma)=5.8\cdot 10^{-5}$ and $B(H\to \mu \bar \mu \gamma)=6.4\cdot 10^{-5}$ 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.
Highlights
Since the discovery of a Higgs boson with a mass of 125 GeV [1,2] in 2012, the LHC experiments CMS and ATLAS put a major effort into the precise determination of its couplings
After the discovery of the 125 GeV Higgs boson Ref. [38] was updated [40] and two new detailed analyses based on novel calculations of the decay rate the decay have rates bdeΓenðHpre→senltþeld−inγÞR=edfps.ffisffi[,41w,4h2e]r.eCpomffisffi pisaritnhge invariant mass of the lepton pair, presented in these papers, we find significant discrepancies, which motivates the new calculation of this decay rate presented in this paper
We have performed a new calculation of the differential decay rate d2ΓðH → lþl−γÞ=ðdsdtÞ, where s is the squared invariant mass of the lepton-antilepton pair and t is the corresponding quantity for the lepton-photon pair
Summary
Since the discovery of a Higgs boson with a mass of 125 GeV [1,2] in 2012, the LHC experiments CMS and ATLAS put a major effort into the precise determination of its couplings. Electroweak loop contributions instead involve the Higgs coupling to heavy gauge bosons or to the top quark and permit a nonzero decay amplitude even for yl 1⁄4 0, producing the lepton pair in a state with angular momentum j 1⁄4 1. We use a linear Rξ gauge, so that we can use the vanishing of the W and Z gauge parameters as a check of our calculation This check is especially valuable in the context of the Z width, which must be taken into account when the invariant mass of the lepton pair is close to the Z boson mass and special care is needed to ensure a gauge-independent result [43,44].
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