Quantum interference among heavy NMSSM Higgs bosons

In the next-to-minimal supersymmetric standard model (NMSSM), it is possible to have strong mass degeneracies between the new singletlike scalar and the heavy doubletlike scalar, as well as between the singletlike and doubletlike pseudoscalar Higgs states. When the difference in the masses of such states is comparable with the sum of their widths, the quantum mechanical interference between their propagators can become significant. We study these effects by taking into account the full Higgs boson propagator matrix in the calculation of the production process of ${\tau }^{+}{\tau }^{-}$ pairs in gluon fusion at the Large Hadron Collider (LHC). We find that, while these interference effects are sizeable, they are not resolvable in terms of the distributions of differential cross sections, owing to the poor detector resolution of the ${\tau }^{+}{\tau }^{-}$ invariant mass. They are, however, identifiable via the inclusive cross sections, which are subject to significant variations with respect to the standard approaches, wherein the propagating Higgs bosons are treated independently from one another. We quantify these effects for several representative benchmark points, extracted from a large set of points, obtained by numerical scanning of the NMSSM parameter space, that satisfy the most important experimental constraints currently available.

Figure 1

${\mathrm{\Lambda }}_{X_i}$ vs $\mathrm{\Delta }{m}_X$ (left), and ${\mathrm{\Gamma }}_{X_i}$ vs $m_{X_1}$ (right), for the points corresponding to scenario 1 (top) and scenario 2 (bottom), obtained from the parameter space scans of the NMSSM. See text for details.

Figure 2

Distributions of the input parameters, showing the correlations among them that lead to a strong mass-degeneracy between $h_s$ and $H$, for the points corresponding to scenario 1 obtained from the numerical scans.

Figure 3

Distributions of the input parameters, showing the correlations among them that lead to a strong mass-degeneracy between $a_s$ and $A$, for the points corresponding to scenario 2 obtained from the numerical scans.

Figure 4

Distributions of the differential cross sections with respect to $\sqrt{\widehat{s}}$ for the six selected BPs. The blue lines correspond to the amplitude containing the full Higgs propagator matrix, and the red lines to the one assuming individual BW propagators.

Figure 5

Distributions of the differential cross sections for the four selected BPs of scenario 1, after convolution with Gaussians of width 150 GeV. The color convention for the lines is the same as in Fig. 4, and the error bars on them correspond to an assumed integrated luminosity of $6000{\mathrm{fb}}^{-1}$.