Search for Higgs boson production in trilepton and like-charge electron-muon final states with the D0 detector

We present a search for Higgs bosons in multilepton final states in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded with the D0 detector at the Fermilab Tevatron Collider, using the full Run II data set with integrated luminosities of up to $9.7{\mathrm{fb}}^{-1}$. The multilepton states considered are $ee\mu$, $e\mu \mu$, $\mu {\tau }_h{\tau }_h$, and like-charge $e^{\pm }{\mu }^{\pm }$ pairs. These channels directly probe the HVV ($V=W$, $Z$) coupling of the Higgs boson in production and decay. The $\mu {\tau }_h{\tau }_h$ channel is also sensitive to $H\to {\tau }^{+}{\tau }^{-}$ decays. Upper limits at the 95% C.L on the rate of standard model Higgs boson production are derived in the mass range $100\le M_H\le 200\mathrm{GeV}$. The expected and observed limits are a factor of 6.3 and 8.4 above the predicted standard model cross section at $M_H=125\mathrm{GeV}$. We also interpret the data in a fermiophobic Higgs boson model.

Figure 1

Distributions of (a) the product of the muon charges, $q_{{\mu }_1}\times q_{{\mu }_2}$, (b) the scalar sum of transverse momenta and ${\mathrm{E̸}}_T$, $\sum _{}^{}{p}_T^{\ell }+{\mathrm{E̸}}_T$, (c) the transverse momentum of the electron, $p_T^e$, (d) the significance $\mathcal{S}({\mathrm{E̸}}_T)$, (e) the maximal $M_{T2}$ for all lepton pairings, $\max \{M_{T2}(\ell {\ell }^{\prime }{\mathrm{E̸}}_T)\}$, and (f) the pseudorapidity of the trilepton system, ${\eta }^{e\mu \mu }$. The distributions are shown after the event selection. The $e\mu {\mu }_{\mathrm{A},\mathrm{B},\mathrm{C}}$ samples are shown in the left, middle, and right columns, respectively. The data are compared to the sum of the expected background and to simulations of a Higgs boson signal for $M_H=125\mathrm{GeV}$, multiplied by a factor of 10 for the $e\mu {\mu }_{\mathrm{A}}$ channel and 75 for the other channels.

Figure 2

Distributions of (a) trilepton transverse momentum, $p_T^{ee\mu }$, and (d) the minimal transverse mass, $\min \{M_T(e_1),M_T(e_2)\}$, for the $ee\mu$ samples, (b) the transverse momentum of the leading ${\tau }_h$ candidate, $p_T^{{\tau }_1}$, and (e) the ditau invariant mass, $M({\tau }_1,{\tau }_2)$, for the $\mu {\tau }_h{\tau }_h$ samples, and (c) missing transverse energy, ${\mathrm{E̸}}_T$, and (f) the invariant mass of the electron and muon, $M_{e\mu }$, for the $e^{\pm }{\mu }^{\pm }$ samples. The distributions are shown after the event selection. In addition, the final selection step requiring the output of the first BDT to be $>0.3$ and $\min \{M_T(e),M_T(\mu )\}>7\mathrm{GeV}$ has also been applied to the $e^{\pm }{\mu }^{\pm }$ sample. The data are compared to the sum of the expected background and to simulations of a Higgs boson signal for $M_H=125\mathrm{GeV}$, multiplied by a factor of 10.

Figure 3

Distribution of the BDT outputs for the (a) $e\mu {\mu }_{\mathrm{A}}$, (b) $e\mu {\mu }_{\mathrm{B}}$, (c) $e\mu {\mu }_{\mathrm{C}}$, and (d) $ee\mu$ channels and distributions of the outputs of the (e,g) first and (f,h) second BDT in the $\mu {\tau }_h{\tau }_h$ and $e^{\pm }{\mu }^{\pm }$ channels, respectively. The data are compared to the sum of the expected background and to simulations of a Higgs boson signal for $M_H=125\mathrm{GeV}$, multiplied by factors of 75 for the $e\mu {\mu }_{\mathrm{B}}$ and $e\mu {\mu }_{\mathrm{C}}$ channels and 10 for the other channels.

Figure 4

Upper limit on the SM Higgs boson production cross section expressed as the ratio to the SM prediction (left column) and observed LLR (right column) as a function of $M_H$ for the (a,b) $ee\mu$, (c,d) $e\mu \mu$, (e,f) $\mu {\tau }_h{\tau }_h$, (g,h) $e^{\pm }{\mu }^{\pm }$ channels, and (i,j) for all channels combined. The LLRs are shown for the background-only and the signal-plus-background hypotheses. The bands correspond to regions of $\pm 1$ and $\pm 2$ standard deviations (s.d.) around the median expected limit and around the expected median LLR for the background-only hypothesis, respectively.

Figure 5

(a) Upper limit on the fermiophobic Higgs boson production cross section expressed as a ratio to the prediction and (b) observed LLR as a function of $M_H$ for the combined channels. Also shown are the expected LLR distributions for the background-only hypothesis and for the $\mathrm{\text{signal}}+\mathrm{\text{background}}$ hypothesis, with the bands indicating $\pm 1$ and $\pm 2$ s.d. fluctuations around the expected median LLR for the background-only hypothesis.