Signal to background interference in $pp\to t{H}^{-}\to t{W}^{-}b\overline{b}$ at the LHC Run II

We investigate in the Large Hadron Collider (LHC) environment the possibility that sizeable interference effects between a heavy charged Higgs boson signal produced via $bg\to t{H}^{-}$ ($+\mathrm{c}.\mathrm{c}.$) scattering and decaying via $H^{-}\to W^{-}A\to W^{-}b\overline{b}$ ($+\mathrm{c}.\mathrm{c}.$) and the irreducible background given by $bg\to t{W}^{-}b\overline{b}$ topologies could spoil current search approaches where the former and latter channels are treated separately. The rationale for this comes from the fact that a heavy charged Higgs state can have a large width, which can also happen for the $CP$-odd neutral Higgs state emerging in the ensuing decays, which in turn enables such interferences. We conclude that effects are very significant, both at the inclusive and exclusive level (i.e., both before and after $H^{\pm }$ selection cuts are enforced, respectively) and typically of a destructive nature. This, therefore, implies that currently established LHC reaches for heavy charged Higgs bosons require some level of rescaling. However, this is possible a posteriori, as the aforementioned $H^{\pm }$ selection cuts shape the interference contributions at the differential level in a way similar to that of the isolated $H^{\pm }$ signal, so there is no need to reassess the efficiency of the individual cuts. We show such effects quantitatively by borrowing benchmark points from different Yukawa types of a 2-Higgs doublet model parameter space for $H^{\pm }$ values starting from around 200 GeV.

Figure 1

Upper panels: Total decay widths (in GeV) of the $CP$-odd $A$ and charged Higgs $H^{\pm }$ bosons in the plane $(m_A,m_{H^{\pm }})$. Lower panels: $\mathrm{BR}(A\to b\overline{b})$ (left) and $\mathrm{BR}(H^{\pm }\to W^{\pm }A)$ (right) in the plane $(m_A,m_{H\pm })$. All panels are for type II.

Figure 2

Same as in Fig. 1 but for type III.

Figure 3

Reconstructed masses of $W^{\pm }$, pseudoscalar $A$, top quark and charged Higgs $H^{\pm }$ for BP5 in the 2HDM flipped.

Figure 4

Reconstructed masses of $W^{\pm }$, pseudoscalar $A$, top quark and charged Higgs $H^{\pm }$ for BP2 in the 2HDM type III.

Figure 5

Distributions for transverse momentum, rapidity and energy of a lepton for signal and interference for BP5 of the 2HDM flipped (top) and BP2 of the 2HDM type III (bottom).

Figure 6

Feynman diagrams in a 2HDM contributing to resonant charged Higgs production and corresponding decays leading to the signal $pp\to t{W}^{-}b\overline{b}$ with $\mathrm{h}\text{−}\equiv H^{-}$, $\mathrm{h}1\equiv h$, $\mathrm{h}2\equiv H$, and $\mathrm{h}3\equiv A$ (as appropriate).

Figure 7

Nonresonant Feynman diagrams contributing to the background for the process $pp\to t{W}^{-}b\overline{b}$ with $\mathrm{h}\text{−}\equiv H^{-}$, $\mathrm{h}1\equiv h$, $\mathrm{h}2\equiv H$, $\mathrm{h}3\equiv A$, and $\mathrm{a}\equiv \gamma$ (as appropriate).

Figure 8

Nonresonant Feynman diagrams contributing to the background for the process $pp\to t{W}^{-}b\overline{b}$ with $\mathrm{h}\text{−}\equiv H^{-}$, $\mathrm{h}1\equiv h$, $\mathrm{h}2\equiv H$, $\mathrm{h}3\equiv A$, and $\mathrm{a}\equiv \gamma$ (as appropriate).

Figure 9

Nonresonant Feynman diagrams contributing to the background for the process $pp\to t{W}^{-}b\overline{b}$ with $\mathrm{h}\text{−}\equiv H^{-}$, $\mathrm{h}1\equiv h$, $\mathrm{h}2\equiv H$, $\mathrm{h}3\equiv A$, and $\mathrm{a}\equiv \gamma$ (as appropriate).