LHC phenomenology of a two-Higgs-doublet neutrino mass model

We study the LHC search prospects for a model in which the neutrinos obtain Dirac masses from couplings to a second Higgs doublet with tiny vacuum expectation value. The model contains a charged Higgs boson that decays to $\ell \nu$ with branching fractions controlled by the neutrino masses and mixing angles as measured in neutrino oscillation experiments. The most promising signal is electroweak production of $H^{+}{H}^{-}$ pairs with decays to $\ell {\ell }^{\prime }{p}_T^{\mathrm{miss}}$, where $\ell {\ell }^{\prime }=e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, and $e^{\pm }{\mu }^{\mp }$. We find that a cut on the kinematic variable $M_{T2}$ eliminates most of the $t\overline{t}$ and $W$-pair background. Depending on the neutrino mass spectrum and mixing angles, a 100 (300) GeV charged Higgs could be discovered at the LHC with as little as $8(24){\mathrm{fb}}^{-1}$ of integrated luminosity at 14 TeV $pp$ center-of-mass energy.

Figure 1

Charged Higgs decay branching fractions to $e\nu$, $\mu \nu$, and $\tau \nu$ as a function of the lightest neutrino mass.

Figure 2

$M_{T2}$ distributions after other cuts have been applied for the $e^{+}{e}^{-}{p}_T^{\mathrm{miss}}$ final state, with $M_{H^{+}}=100\mathrm{GeV}$ (left, with jet veto) and 300 GeV (right, no jet veto). For the signal we take $\mathrm{BR}(H^{+}\to e^{+}\nu )=1/3$, which occurs for a degenerate neutrino spectrum. The $M_{T2}$ cut window is shown by the vertical lines.

Figure 3

Luminosity required at the LHC (14 TeV) for a $5\sigma$ discovery if $M_{H^{+}}=100\mathrm{GeV}$, for the normal hierarchy (NH, left) and inverted hierarchy (IH, right). The lines for each channel bound the range of required luminosities obtained by scanning over the $2\sigma$ allowed ranges of the parameters of the neutrino mixing matrix and mass-squared differences.

Figure 4

As in Fig. 3 but for $M_{H^{+}}=300\mathrm{GeV}$.