Searches for heavy Higgs bosons in two-Higgs-doublet models and for $t\to ch$ decay using multilepton and diphoton final states in $pp$ collisions at 8 TeV

Searches are presented for heavy scalar ($H$) and pseudoscalar ($A$) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of $pp$ collisions collected with the CMS experiment at the LHC at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$ and corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$. The decays $H\to hh$ and $A\to Zh$, where $h$ denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. The search results are presented in terms of the $H$ and $A$ production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on $\sigma \mathcal{B}$ for $H\to hh$ and 2 pb for $A\to Zh$. Also presented are the results of a search for the rare decay of the top quark that results in a charm quark and an SM Higgs boson, $t\to ch$, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on $\mathcal{B}(t\to ch)$.

Figure 1

(Top panel) Diphoton invariant mass distribution for $\gamma \gamma {\tau }_{\mathrm{h}}$ events with $E_{\mathrm{T}}^{\text{miss}}<30\mathrm{GeV}$ with an exponential fit derived from the 100–120 and 130–200 GeV sidebands regions. (Bottom panel) The same distribution for the $\gamma \gamma \ell$ events with $E_{\mathrm{T}}^{\text{miss}}$ in 30–50 GeV range with an exponential fit (blue curve) where the exponent is fixed to the value obtained from the fit shown in the top figure. Also shown for comparison purposes is an actual fit (magenta curve) to the shown data distribution. An example signal distribution (in red), assuming $\sigma \mathcal{B}(pp\to H\to hh)$ to be equal to three times 3.59 pb, as described in the text, shows that the signal is well contained in the 120–130 GeV window.

Figure 2

The $E_{\mathrm{T}}^{\text{miss}}$ distributions for four-lepton events with an off-$Z$ OSSF1 dilepton pair, no $b$-tagged jet, no ${\tau }_{\mathrm{h}}$ (top panel), and one ${\tau }_{\mathrm{h}}$ (bottom panel). These nonresonant (off-$Z$) channels are sensitive to the $H\to hh$ signal which is shown stacked on top of the background distributions, assuming $\sigma \mathcal{B}(pp\to H\to hh)=3.59\mathrm{pb}$, as described in the text.

Figure 3

The $E_{\mathrm{T}}^{\text{miss}}$ distributions for four-lepton events without $b$-tagged jets which contain an on-$Z$ OSSF1 dilepton pair and one ${\tau }_{\mathrm{h}}$ (top panel), and an OSSF2 dilepton pair with one $Z$ candidate and no ${\tau }_{\mathrm{h}}$ (bottom panel). These resonant (containing a $Z$) channels are sensitive to the $A\to Zh$ signal which is shown stacked on top of the background distributions, assuming $\sigma \mathcal{B}(pp\to A\to Zh)=3.59\mathrm{pb}$, as described in the text.

Figure 4

(Top panel) Observed and expected 95% C.L. $\sigma \mathcal{B}$ limits for gluon fusion production of $H$ and the decay $H\to hh$ with one and two standard deviation bands shown. These limits are based only on multilepton channels. The $h$ branching fractions are assumed to have SM values. (Bottom panel) The same, but also including $\text{lepton}+\text{diphoton}$ channels.

Figure 5

(Top panel) Observed and expected 95% C.L. $\sigma \mathcal{B}$ limits for gluon fusion production of $A$ and the decay $A\to Zh$ with one and two standard deviation bands shown. These limits are based only on multilepton channels. The $h$ branching fraction are assumed to have SM values. (Bottom panel) The same, but also including $\text{lepton}+\text{diphoton}$ channels.

Figure 6

(Left panels) Observed and expected 95% C.L. upper limits for gluon fusion production of a heavy Higgs boson $H$ of mass 300 GeV as a function of parameters $\tan \beta$ and $\cos (\beta -\alpha )$ of the types I (upper panel) and II (lower panel) 2HDM. The parameters determine the $H$ production cross section as well as the branching fractions $\mathcal{B}(H\to hh)$ and $\mathcal{B}(h\to W{W}^{*},Z{Z}^{*},\tau \tau ,\gamma \gamma )$, which are relevant to this search. (Right panel) The $\sigma \mathcal{B}(H\to hh)$ contours for types I (upper panel) and II (lower panel) 2HDM adopted from Ref. [35]. The excluded regions are either below the open limit contours or within the closed ones.

Figure 7

(Left panels) Observed and expected 95% C.L. upper limits for gluon fusion production of an $A$ boson of mass 300 GeV as a function of parameters $\tan \beta$ and $\cos (\beta -\alpha )$ of the types I (upper panel) and II (lower panel) 2HDM. The parameters determine the $A$ production cross section as well as the branching fractions $\mathcal{B}(A\to Zh)$ and $\mathcal{B}(h\to W{W}^{*},Z{Z}^{*},\tau \tau ,\gamma \gamma )$ which are relevant to this search. (Right panels) The $\sigma \mathcal{B}(A\to Zh)$ contours for types I (upper panel) and II (lower panel) 2HDM adopted from Ref. [35]. The excluded regions are below the open limit contours.

Figure 8

Combined observed and expected 95% upper limits for gluon fusion production of a heavy Higgs boson $H$ and $A$ of mass 300 GeV for type I (top panel) and type II (bottom panel) 2HDM as a function of parameters $\tan \beta$ and $\cos (\beta -\alpha )$. The parameters determine the $H$ and $A$ production cross sections as well as the branching fractions $\mathcal{B}(H\to hh)$, $\mathcal{B}(A\to Zh)$, and $\mathcal{B}(h\to W{W}^{*},Z{Z}^{*},\tau \tau ,\gamma \gamma )$, which are relevant to this search.