Search for a Low-Mass Higgs Boson in ${\rm Y}(3S)\to \gamma A^0$, $A^0\to {\tau }^{+}{\tau }^{-}$ at BABAR

We search for a light Higgs boson $A^0$ in the radiative decay ${\rm Y}(3S)\to \gamma A^0$, $A^0\to {\tau }^{+}{\tau }^{-}$, ${\tau }^{+}\to e^{+}{\nu }_e{\overline{\nu }}_{\tau }$, or ${\tau }^{+}\to {\mu }^{+}{\nu }_{\mu }{\overline{\nu }}_{\tau }$. The data sample contains $122\times {10}^6$ ${\rm Y}(3S)$ events recorded with the BABAR detector. We find no evidence for a narrow structure in the studied ${\tau }^{+}{\tau }^{-}$ invariant mass region of $4.03<m_{{\tau }^{+}{\tau }^{-}}<10.10\mathrm{GeV}/c^2$. We exclude at the 90% confidence level (C.L.) a low-mass Higgs boson decaying to ${\tau }^{+}{\tau }^{-}$ with a product branching fraction $\mathcal{B}\mathbf{(}{\rm Y}(3S)\to \gamma A^0\mathbf{)}\times \mathcal{B}(A^0\to {\tau }^{+}{\tau }^{-})>(1.5–16)\times {10}^{-5}$ across the $m_{{\tau }^{+}{\tau }^{-}}$ range. We also set a 90% C.L. upper limit on the ${\tau }^{+}{\tau }^{-}$ decay of the ${\eta }_b$ at $\mathcal{B}({\eta }_b\to {\tau }^{+}{\tau }^{-})<8\%$.

Figure 1

(a), (c), (e): $E_{\gamma }$ distributions for the different $\tau \tau$-decay modes. Filled circles show the data; dotted lines represent contributions from ${\rm Y}(3S)\to \gamma {\chi }_{bJ}(2P)$, ${\chi }_{bJ}(2P)\to \gamma {\rm Y}(2S)$; dotted-dashed lines show contributions from ${\rm Y}(3S)\to \gamma {\chi }_{bJ}(2P)$, ${\chi }_{bJ}(2P)\to \gamma {\rm Y}(1S)$; and solid lines show the total background function. For each $\tau \tau$-decay mode, the difference between the background function and the data divided by the uncertainty in the data is shown [(b), (d), (f)].

Figure 2

$N_{\mathrm{sig}}/\sigma (N_{\mathrm{sig}})$ as obtained from the scanning procedure. Only statistical uncertainties are included. The curve shows the standard normal distribution with a normalization factor of 307.

Figure 3

(a) Product branching fractions as a function of the Higgs mass. For each point, both the statistical uncertainty (from the central value to the horizontal bar) and the total uncertainty (statistical and systematic added in quadrature) are shown (from the central value to the end of the error bar). In (b), the corresponding 90% C.L. upper limits on the product of the branching fractions versus the Higgs mass values are shown, with total uncertainty (solid line) and statistical uncertainty only (dashed line). The shaded vertical region represents the excluded mass range corresponding to the ${\chi }_{bJ}(2P)\to \gamma {\rm Y}(1S)$ states.