Triangle singularity in $B^0\to {\pi }^{-}{K}^{+}X(3872)$ via the $D_{s1}\bar{D}{D}^{\ast }$ loop and possible precise measurement of the $X(3872)$ mass

Abstract

We investigate the $B^0\to {\pi }^{-}{K}^{+}X(3872)$ decay via the $D_{s1}(2536)\bar{D}{D}^{\ast }$ rescattering diagram. The line shape of the $K^{+}X(3872)$ distribution curve around $D_{s1}(2536)\bar{D}$ threshold is very sensitive to the $X(3872)$ mass because the triangle singularity (TS) can be generated from the loop. By means of this characteristic, we can determine whether the $X(3872)$ mass is below or above the $D^{\ast 0}{\bar{D}}^0$ threshold with high precision. The narrowness of $D_{s1}(2536)$ in the loop is one of the key reasons why the TS mechanism of measuring the $X(3872)$ mass may work. The $X(3872)$ width impact on the $K^{+}X(3872)$ line shape is also crucial in the TS mechanism. If the width is as large as 1 MeV, the proposed method of measuring the $X(3872)$ mass would be ruined.

Comments: 6 pages, 3 figures