RIP Hb(b)over-bar: how other Higgs production modes conspire to kill a rare signal at the LHC

The hadroproduction of a Higgs boson in association with a bottom-quark pair (Hbb¯) is commonly considered as the key process for directly probing the Yukawa interaction between the Higgs boson and the bottom quark (yb). However, in the Standard-Model (SM) this process is also known to suffer from very large irreducible backgrounds from other Higgs production channels, notably gluon-fusion (ggF). In this paper we calculate for the first time the so-called QCD and electroweak complete-NLO predictions for Hbb¯ production, using the four-flavour scheme. Our calculation shows that not only the ggF but also the ZH and even the vector-boson-fusion channels are sizeable irreducible backgrounds. Moreover, we demonstrate that, at the LHC, the rates of these backgrounds are very large with respect to the “genuine” and yb-dependent Hbb¯ production mode. In particular, no suppression occurs at the differential level and therefore backgrounds survive typical analysis cuts. This fact further jeopardises the chances of measuring at the LHC the yb-dependent component of Hbb¯ production in the SM. Especially, unless yb is significantly enlarged by new physics, even for beyond-the SM scenarios the direct determination of yb via this process seems to be hopeless at the LHC.