LHC constraints on a Higgs boson partner from an extended color sector

We discuss the properties and LHC phenomenology of a potentially discoverable heavy scalar boson ($s$) that arises in the context of the renormalizable coloron model; the model also contains a light scalar, $h$, identifiable with the 125 GeV state discovered by the LHC. These two scalar mass eigenstates are admixtures of a weak doublet gauge eigenstate and a weak singlet gauge eigenstate. A previous study set exclusion limits on the heavy $s$ scalar, using the stability of the scalar potential, unitarity, electroweak precision tests, and LHC searches for the 125 GeV Higgs; it also briefly discussed the $\sqrt{s}=7$, 8 TeV LHC searches for a heavy Higgs. In this work, we show how the projected LHC sensitivity at $\sqrt{s}=14\mathrm{TeV}$ to the presence of a heavy Higgs and to the detailed properties of the 125 GeV Higgs will further constrain the properties of the new heavy $s$ scalar. Since the renormalizable coloron model may contain spectator fermions to remove anomalies, we examine several representative scenarios with different numbers of spectator fermions. Our results are summarized in plots that overlay the current exclusion limits on the $s$ boson with the projected sensitivity of the $\sqrt{s}=14\mathrm{TeV}$ LHC to the new state. We find that the upcoming LHC searches should be sensitive to an $s$ scalar of mass less than 1 TeV for essentially all of the model parameter space in which the $h$ state differs from the Higgs boson of the SM. More precisely, unless the mixing between the weak doublet and weak singlet gauge-eigenstate scalars is zero, the 14 TeV LHC will be sensitive to the presence of the nonstandard heavy $s$ state that is characteristic of the renormalizable coloron model.

Figure 1

The ratio of the $s$ boson’s total width to its mass as a function of its mass for the range $200\le m_s\le 1000\mathrm{GeV}$, exhibiting the validity of the narrow-width approximation. The panels correspond to three benchmark values of the singlet VEV, $v_s$, each displaying this ratio for three different mixing angles, $\sin \chi$, as motivated by the experimental searches [9]. A “light” pseudoscalar ($m_{\mathcal{A}}=50\mathrm{GeV}$) and scalar color octet ($m_{G_H}=150\mathrm{GeV}$) have been chosen to make the width as broad as possible for the entire range of $m_s$, demonstrating the “worst-case” scenarios. The ratio is, furthermore, insensitive to the (TeV range) coloron and spectator masses, and the number of spectator fermion generations.

Figure 2

The heavy $s$ Higgs production cross section times its vector boson decay branching ratio, divided by that of a corresponding SM $h_0$ Higgs with the same mass, as parametrized by $\mu$ in (27), for $200\le m_s\le 1000\mathrm{GeV}$. The LHC $\sqrt{s}=7$, 8 TeV heavy Higgs exclusion limits at 95% C.L. [14, 15] are displayed by the dot-dashed line, with the most stringent bounds arising from the $WW$ and $ZZ$ final states. These data are complemented by the $\sqrt{s}=14\mathrm{TeV}$ projected exclusion limits at 95% C.L. with an integrated luminosity of 300 and $3000{\mathrm{fb}}^{-1}$ for ATLAS (solid lines) assuming a SM-like heavy Higgs [16], and for CMS (dashed lines) assuming a heavy Higgs in the 2HDM [17, 18]. In both 14 TeV projections, the strongest limits are determined by the $ZZ$ final states.

Figure 3

95% C.L. exclusion contours for the scenario with no spectator fermion generation, $N_Q=0$, represented in the $m_s-\sin \chi$ plane, covering the heavy $s$ scalar mass range $200\le m_s\le 1000\mathrm{GeV}$ and the full range of mixing angle values $-1\le \sin \chi \le 1$. A universal pseudoscalar mass, $m_{\mathcal{A}}=150\mathrm{GeV}$, has been used for the purpose of illustration. Three selected values of the singlet VEV, $v_s$, are displayed in the three rows, within which the scalar color-octet mass, $m_{G_H}$, is varied from light (left plot) to heavy (right plot). The exclusion limits arise from imposing unitarity (dot-dashed purple), electroweak precision tests (dotted orange), LHC direct measurements of the 125 GeV $h$ Higgs (vertical dashed gray), and the $\sqrt{s}=7$, 8 TeV LHC heavy $s$ boson searches (solid yellow). The inclined-shaded green region corresponds to the heavy $s$ boson exclusion projections for $\sqrt{s}=14\mathrm{TeV}$ ATLAS with an integrated luminosity of $300{\mathrm{fb}}^{-1}$. Given their heavy nature, the dependence on the coloron and spectator masses, $M_C$ and $M_Q$, is negligible throughout.

Figure 4

95% C.L. exclusion contours for the scenario with one spectator fermion generation, $N_Q=1$, represented in the $m_s-\sin \chi$ plane, covering the heavy $s$ scalar mass range $200\le m_s\le 1000\mathrm{GeV}$ and the full range of mixing angle values $-1\le \sin \chi \le 1$. (For details, see the caption of Fig. 3.)

Figure 5

95% C.L. exclusion contours for the scenario with three spectator fermion generations, $N_Q=3$, represented in the $m_s-\sin \chi$ plane, covering the heavy $s$ scalar mass range $200\le m_s\le 1000\mathrm{GeV}$ and the full range of mixing angle values $-1\le \sin \chi \le 1$. The additional horizontally shaded gray region in the $v_s=5\mathrm{TeV}$ case accounts for the exclusion by more precise measurements of the 125 GeV $h$ Higgs. (For details, see the caption of Fig. 3.)