Model-independent probe of anomalous heavy neutral Higgs bosons at the LHC

We first formulate, in the framework of the effective Lagrangian, the general form of the effective interactions of the lightest Higgs boson $h$ and a heavier neutral Higgs boson $H$ in a multi-Higgs system taking account of the Higgs mixing effect. We regard $h$ as the discovered Higgs boson which has been shown to be consistent with the standard model Higgs boson. The obtained effective interactions contain extra parameters reflecting the Higgs mixing effect. Next, we study the constraints on the anomalous coupling constants of $H$ from both the requirement of the unitarity of the $S$ matrix and the exclusion bounds on the standard model Higgs boson obtained from the experimental data at the 7–8 TeV LHC. From this we obtain the available range of the anomalous coupling constants of $H$, with which $H$ is not excluded by the yet known theoretical and experimental constraints. We then study the signatures of $H$ at the 14 TeV LHC. In this paper, we suggest taking weak-boson scattering and $pp\to V{H}^{*}\to VVV$ as sensitive processes for probing $H$ model independently at the 14 TeV LHC. We take several examples with the anomalous $HVV$ coupling constants in the available ranges to do the numerical study. A full tree-level calculation at the hadron level is given with signals and backgrounds carefully calculated. We impose a series of proper kinematic cuts to effectively suppress the backgrounds. It is shown that, in both the $VV$ scattering and the $pp\to V{H}^{*}\to VVV$ processes, the $H$ boson can be discovered from the invariant mass distributions of the final state particles with reasonable integrated luminosity. Especially, in the $pp\to V{H}^{*}\to VVV$ process, the invariant mass distribution of the final state jets can show a clear resonance peak of $H$. Finally, we propose several physical observables from which the values of the anomalous coupling constants $f_W$ and $f_{WW}$ can be measured experimentally.

Figure 1

Illustration of the momenta in the $HVV$ interactions in Eq. (10).

Figure 2

Unitarity bounds on $f_W$ and $f_{WW}$ in which (a) is with ${\rho }_h=0.8$ and ${\rho }_H=0.6$; (b) is with ${\rho }_h=0.9$ and ${\rho }_H=0.4$. The red and blue-dashed contours are boundaries of the allowed regions obtained from $W_L^{+}{W}_L^{-}\to VV$ [Eq. (23)] and $Z_L{Z}_L\to VV$ [Eq. (24)], respectively.

Figure 3

Obtained experimental bound on $f_W$ and $f_{WW}$ in the case of 400II. The blue shaded region is the available region.

Figure 4

Obtained experimental bound on $f_W$ and $f_{WW}$ in the case of 500I. The blue shaded region is the available region.

Figure 5

Obtained experimental bound on $f_W$ and $f_{WW}$ in the case of 500II. The blue shaded region is the available region.

Figure 6

Feynman diagrams in weak-boson scattering. (a) The signal, (b) examples of the IB.

Figure 7

Feynman diagrams for QCD backgrounds of $W+3j$.

Figure 8

Feynman diagrams for QCD backgrounds of $WV+2j$.

Figure 9

Feynman diagrams for the top-quark backgrounds.

Figure 10

$p_T(\text{leptons})$ distributions of $\text{signal}+\mathrm{IB}$ (red-solid), IB (pink-dotted), and total RBs (blue-small-dotted) in weak-boson scattering for example 500II with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 11

$M(J,j)$ distributions of $\text{signal}+\mathrm{IB}$ (red-solid) and the top-quark background (blue-dotted) in weak-boson scattering for example 500II with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 12

Invariant mass $M(J_1,\text{recons}W)$ distributions (red-solid) for the five examples [(a) 400II, (b) 500I, (c) 500II, (d) 800I, and (e) 800II], together with that of the SM (blue-dotted) for comparison, with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 13

Feynman diagrams in $VH$ associated production. (a) The signal, (b) examples of the IB.

Figure 14

$p_T(\text{leptons})$ distributions of $\text{signal}+\mathrm{IB}$ (red-solid), IB (pink-dotted), and total RBs (blue-small-dotted) in the $pp\to V{H}^{*}\to VVV$ process for example 500II with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 15

$M(J,j)$ distributions of $\text{signal}+\mathrm{IB}$ (red-solid) and the top-quark background (blue-dotted) in the $pp\to V{H}^{*}\to VVV$ process for example 500II with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 16

$\mathrm{\Delta }R({\ell }^{+},J_1)$ distributions of $\text{signal}+\mathrm{IB}$ (red-solid) and the total background (blue-dotted) in the $pp\to V{H}^{*}\to VVV$ process for example 500II with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 17

Invariant masses $M(J_1,J_2)$ in the $pp\to V{H}^{*}\to VVV$ process after all cuts and $\mathrm{\Delta }R({\ell }^{+},J_2)>2$, 5 for the following examples: (a) 400II, (b) 500I, (c) 500II, and (d) 800II.

Figure 18

$\mathrm{\Delta }R({\ell }^{+},J_2)$ distributions of $\text{signal}+\mathrm{IB}$ (red-dotted) and the total background (dark-solid) in the $pp\to V{H}^{*}\to VVV$ process for example 800I with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$.

Figure 19

(a) The $p_T(\text{leptons})$ distribution [with (56) and $\mathrm{\Delta }R({\ell }^{+},J_2)>2.5$], (b) the $p_T(J_1)$ distribution [with (56) and $\mathrm{\Delta }R({\ell }^{+},J_2)>2.5$], (c) the $\mathrm{\Delta }R({\ell }^{+},J_2)$ distribution [without (56) and $\mathrm{\Delta }R({\ell }^{+},J_2)>2.5$], and (d) the $\mathrm{\Delta }R(J_1,J_2)$ distribution [without (56) and $\mathrm{\Delta }R({\ell }^{+},J_2)>2.5$], with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$. The dark-solid, red-dotted, pink-dashed, and blue-dashed-dotted curves stand for set I, set II, set III and set IV, respectively.

Figure 20

(a) The $p_T(J_1)$ distribution and (b) the $\mathrm{\Delta }R(J_1,J_2)$ distribution for $M_H=800\mathrm{GeV}$ with ${\mathsf{L}}_{\text{int}}=100{\mathrm{fb}}^{-1}$. The meaning of the curves is the same as in Fig. 19 but with $C_t=1$.

Figure 21

Check of unitarity: (a) $M(J,\text{leptons})$ distribution in weak-boson scattering, (b) $M(J_2,\text{leptons})$ distribution, and (c) $M(J_1,J_2)$ distribution in the $pp\to V{H}^{*}\to VVV$ process.