Constraints on Models for the Higgs Boson with Exotic Spin and Parity in $VH\to Vb\overline{b}$ Final States

We present constraints on models containing non-standard-model values for the spin $J$ and parity $P$ of the Higgs boson $H$ in up to $9.7{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected with the D0 detector at the Fermilab Tevatron Collider. These are the first studies of Higgs boson $J^P$ with fermions in the final state. In the $ZH\to \ell \ell b\overline{b}$, $WH\to \ell \nu b\overline{b}$, and $ZH\to \nu \nu b\overline{b}$ final states, we compare the standard model (SM) Higgs boson prediction, $J^P=0^{+}$, with two alternative hypotheses, $J^P=0^{-}$ and $J^P=2^{+}$. We use a likelihood ratio to quantify the degree to which our data are incompatible with non-SM $J^P$ predictions for a range of possible production rates. Assuming that the production rate in the signal models considered is equal to the SM prediction, we reject the $J^P=0^{-}$ and $J^P=2^{+}$ hypotheses at the 97.6% CL and at the 99.0% CL, respectively. The expected exclusion sensitivity for a $J^P=0^{-}$ ($J^P=2^{+}$) state is at the 99.86% (99.94%) CL. Under the hypothesis that our data are the result of a combination of the SM-like Higgs boson and either a $J^P=0^{-}$ or a $J^P=2^{+}$ signal, we exclude a $J^P=0^{-}$ fraction above 0.80 and a $J^P=2^{+}$ fraction above 0.67 at the 95% CL. The expected exclusion covers $J^P=0^{-}$ ($J^P=2^{+}$) fractions above 0.54 (0.47).

Figure 1

(a) Invariant mass of the $\ell \ell b\overline{b}$ system in the $ZH\to \ell \ell b\overline{b}$ high-purity double-tag (DT HP) channel, (b) transverse mass of the $\ell \nu b\overline{b}$ system in the $WH\to \ell \nu b\overline{b}$ high-purity two-tight-tag (2TT HP) channel, and (c) transverse mass of the $\nu \nu b\overline{b}$ system in the $ZH\to \nu \nu b\overline{b}$ high-purity tight-tag (TT HP) channel. The $J^P=0^{-}$ and $J^P=2^{+}$ samples are normalized to the product of the SM cross section and branching fraction multiplied by an additional factor. Heavy- and light-flavor quark jets are denoted by lf and hf, respectively. Overflow events are included in the highest mass bin. For all signals, a mass of 125 GeV for the $H$ or $X$ boson is assumed.

Figure 2

LLR distributions comparing the $J^P=0^{+}$ and the $J^P=2^{+}$ hypotheses for the combination. The $J^P=0^{+}$ and $J^P=2^{+}$ samples are normalized to the product of the SM cross section and branching fraction. The vertical solid line represents the observed LLR value assuming $\mu =1.0$, while the dark and light shaded areas represent the 1 and 2 standard deviations (s.d.) on the expectation from the null hypothesis $H_0$, respectively.

Figure 3

The expected exclusion region (shaded area) and observed exclusion (solid line) as functions of the $J^P=0^{-}$ and $J^P=0^{+}$ signal strengths. The expected exclusion region (hatched area) and observed exclusion (dashed line) as functions of the $J^P=2^{+}$ and $J^P=0^{+}$ signal strengths.

Figure 4

$1-\mathrm{C}{\mathrm{L}}_s$ as a function of the $J^P=0^{-}$ signal fraction assuming the product of the total cross section and branching ratio is equal to the SM prediction. The horizontal line corresponds to the 95% CL exclusion. The dark and light shaded regions represent the 1 and 2 s.d. fluctuations for the $J^P=0^{+}$ hypothesis.