Searching for H→hh→bb¯ττ in the 2HDM type-I at the LHC

Unlike other realizations of the 2-Higgs doublet model (2HDM), the so-called type-I allows for a very light Higgs boson spectrum. Specifically, herein, the heaviest of the two <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>C</a:mi><a:mi>P</a:mi></a:math>-even neutral Higgs states, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>H</c:mi></c:math>, can be the one discovered at the Large Hadron Collider (LHC) in 2012, with a mass of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo>≈</e:mo><e:mn>125</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>GeV</e:mi></e:math> and couplings consistent with those predicted by the Standard Model (SM). In such a condition of the model, referred to as “inverted mass hierarchy,” the decay of the SM-like Higgs state into pairs of the lightest <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>C</g:mi><g:mi>P</g:mi></g:math>-even neutral Higgs boson, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>h</i:mi></i:math>, is possible, for masses of the latter ranging from <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msub><k:mi>M</k:mi><k:mi>H</k:mi></k:msub><k:mo>/</k:mo><k:mn>2</k:mn><k:mo>≈</k:mo><k:mn>65</k:mn><k:mtext> </k:mtext><k:mtext> </k:mtext><k:mi>GeV</k:mi></k:math> down to 15 GeV or so, all compatible with experimental constraints. In this paper, we investigate the scope of the LHC in accessing the process <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>g</m:mi><m:mi>g</m:mi><m:mo stretchy="false">→</m:mo><m:mi>H</m:mi><m:mo stretchy="false">→</m:mo><m:mi>h</m:mi><m:mi>h</m:mi><m:mo stretchy="false">→</m:mo><m:mi>b</m:mi><m:mover accent="true"><m:mi>b</m:mi><m:mo stretchy="false">¯</m:mo></m:mover><m:mi>τ</m:mi><m:mi>τ</m:mi></m:math> by performing a Monte Carlo (MC) analysis aimed at extracting this signal from the SM backgrounds, in presence of a dedicated trigger choice and kinematic selection. We prove that some sensitivity to such a channel exists already at run 3 of the LHC while the High-Luminosity LHC (HL-LHC) will be able to either confirm or disprove this theoretical scenario over sizable regions of its parameter space.