Low-mass doubly charged Higgs bosons at the LHC

Search for light (within the mass range 84–200 GeV) doubly charged Higgs bosons decaying into a pair of $W$ bosons has been deemed challenging using the conventional LHC searches with leptons, jets, and missing transverse momentum in the final state. Such Higgses, together with slightly heavier singly-charged and neutral Higgses, when arranged in an $SU(2{)}_L$ triplet as in the type-II seesaw model, have been recently shown to accommodate the recent measurement of the $W$-boson mass by the CDF Collaboration. When produced in a highly Lorentz-boosted regime, these tend to manifest as a single fat jet or a pair of adjacent same-sign leptons plus missing transverse momentum. First, we perform a multivariate analysis to discern such exotic jets from the standard model jets. Then, we present a novel search in the final state with an exotic jet and two same-sign leptons plus missing transverse momentum. We find that such low-mass doubly charged Higgses could be directly probed with the already collected Run 2 LHC data.

Figure 1

Theoretically allowed $m_{H^{\pm \pm }}\text{−}\mathrm{\Delta }m$ parameter space for $v_t=1\mathrm{GeV}$.

Figure 2

LO $pp\to H^{++}{H}^{--}$ cross section at the 13 TeV LHC.

Figure 3

Schematic Feynman diagram for $q\overline{q}\to H^{++}{H}^{--}$ and its subsequent decays to one $H^{\pm \pm }$ jet, two same-sign leptons, and neutrinos.

Figure 4

Normalized distributions for some of the input features. The signal distributions are for $m_{H^{\pm \pm }}=150\mathrm{GeV}$.

Figure 5

Correlations in percent among the input features for the $H^{\pm \pm }$ jets (left) and the SM jets (right).

Figure 6

BDT response curves for the training and testing subsamples.

Figure 7

BDT performance in terms of the ROC curve (left) and the signal (with $m_{H^{\pm \pm }}=150\mathrm{GeV}$) and background efficiencies as a function of the BDT response.

Figure 8

The signal efficiency as a function of $m_{H^{\pm \pm }}$ for the BDT response of 0.1.

Figure 9

Normalized distribution for the signal with $m_{H^{\pm \pm }}=150\mathrm{GeV}$ and background events. (From the left to right) first: $m_{\ell \ell }$ after the S1 cut; second, third, and fourth: $p_T^{\mathrm{miss}}$, $\mathrm{\Delta }{R}_{\ell \ell }$, and $\mathrm{\Delta }\varphi (\ell \ell ,p_T^{\mathrm{miss}})$, respectively, after the S2 cut.

Figure 10

Required luminosity (${\mathrm{fb}}^{-1}$) for the $5\sigma$ discovery and 95% exclusion for different $m_{H^{\pm \pm }}$.