Abstract
We study the inclusive production of a Higgs boson in association with a high-$p_T$ photon at the LHC, detailing the leading-order features of the main processes contributing to the $H\gamma$ final state. Requiring an extra hard photon in Higgs production upsets the cross-section hierarchy for the dominant channels. The $H\gamma$ inclusive production comes mainly from photons radiated in vector-boson fusion (VBF), which accounts for about 2/3 of the total rate, for $p_T^{\gamma,j} >30$ GeV, at leading order. On the other hand, radiating a high-$p_T$ photon in the main top-loop Higgs channel implies an extra parton in the final state, which suppresses the production rate by a further $\alpha_S$ power. As a result, the $H\gamma$ production via top loops at the LHC has rates comparable with the ones arising from either the $H t\bar t$ production or the $HW(Z)\gamma$ associated production. Then, in order of decreasing cross section, comes the single-top-plus-Higgs channel, followed in turn by the heavy-flavor fusion processes $b\bar b \to H\gamma$ and $c\bar c \to H\gamma$. The $H\gamma$ production via electroweak loops has just a minor role. At larger c.m. energies, the $H t\bar t\gamma$ channel surpasses the total contribution of top-loop processes. In particular, requiring $p_T^{\gamma,j} >30$ GeV at $\sqrt S \simeq 100$ TeV, $H t\bar t\gamma$ accounts for about $1/4$ of the inclusive $H\gamma$ production at leading order, about half of the total being due to VBF production.
Highlights
Httγ accounts for about 1/4 of the inclusive Hγ production at leading order, about half of the total being due to vector-boson fusion (VBF) production
We study the inclusive production of a Higgs boson in association with a high-pT photon at the LHC, detailing the leading-order features of the main processes contributing to the Hγ final state
The Hγ inclusive production comes mainly from photons radiated in vector-boson fusion (VBF), which accounts for about 2/3 of the total rate, for pγT,j > 30 GeV, at leading order
Summary
We detail the present theoretical knowledge of the various channels contributing to the associated production of a Higgs boson and a high-pT photon at the LHC. When asking for an extra photon in the main Higgs production channel gg → H proceeding via gluon fusion into a top triangle loop, one is forced to pass to the QCD order, and include an extra parton in the collision final state. In [10], the gg → Hγg rate has been compared to the heavy-quark QQ + Qg → Hγj cross section (with Q = b, c), and claimed to provide the dominant contribution to the Hγj final state at hadron colliders We correct the latter statement, by including the Hγj production initiated by light quarks, proceeding via the top triangle ggH vertex in either the t-channel (figure 2) or the s-channel (figure 3). At the 14-TeV LHC, the light-quark initiated contribution to the Hγj production turns out to be an order of magnitude larger than the pentagon gluon-fusion production (cf. eqs. (2.3) and (2.6))
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