Search for a light Higgs boson in single-photon decays of $\hat{I}\yen (1S)$ using $\hat{I}\yen (2S)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\yen (1S)$ tagging method

Abstract

We search for a light Higgs boson ($A^0$) decaying into a $\ddot{I}{„}^{+}\ddot{I}{„}^{-}$ or $\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ pair in the radiative decays of $\hat{I}\yen (1S)$. The production of $\hat{I}\yen (1S)$ mesons is tagged by $\hat{I}\yen (2S)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\yen (1S)$ transitions, using 158 million $\hat{I}\yen (2S)$ events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $A^0$ signals in the mass range from the $\ddot{I}{„}^{+}\ddot{I}{„}^{-}$ or $\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ threshold to 9.2 GeV/$c^2$ are observed. We set the upper limits at 90\% credibility level (C.L.) on the product branching fractions for $\hat{I}\yen (1S)\to {\hat{I}}^3{A}^0$ and $A^0\to \ddot{I}{„}^{+}\ddot{I}{„}^{-}$ varying from $3.8\times 10^{-6}$ to $1.5\times 10^{-4}$. Our results represent an approximately twofold improvement on the current world best upper limits for the $\hat{I}\yen (1S)\to {\hat{I}}^3{A}^0(\to \ddot{I}{„}^{+}\ddot{I}{„}^{-})$ production. For $A^0\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$, the upper limits on the product branching fractions for $\hat{I}\yen (1S)\to {\hat{I}}^3{A}^0$ and $A^0\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ are at the same level as the world average limits, and vary from $3.1\times 10^{-7}$ to $1.6\times 10^{-5}$. The upper limits at 90\% C.L. on the Yukawa coupling $f_{\hat{I}\yen (1S)}$ and mixing angle $\sin \hat{I}{¸}_{A^0}$ are also given.

9 pages, 5 figures; accepted for publication as a Letter in Physical Review Letters