First evidence for $D_s^{+}\to f_1(1420)e^{+}\hat{I}{½}_e$ and search for $D_s^{+}\to f_1(1285)e^{+}\hat{I}{½}_e$

Abstract

Using $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of 7.33~$\mathrm{f}{\mathrm{b}}^{-1}$ recorded by the BESIII detector at center-of-mass energies between 4.128 and 4.226~$\mathrm{GeV}$, we present the first search for the semileptonic decays $D_s^{+}\to f_1(1420)e^{+}\hat{I}{½}_e$ and $D_s^{+}\to f_1(1285)e^{+}\hat{I}{½}_e$. The first evidence for the decay $D_s^{+}\to f_1(1420)e^{+}\hat{I}{½}_e$ is found with a statistical significance of 3.4$\ddot{I}ƒ$, and its product branching fraction $\mathcal{B}(D_s^{+}\to f_1(1420)e^{+}\hat{I}{½}_e)\cdot \mathcal{B}(f_1(1420)\to K^{+}{K}^{-}\ddot{I}{€}^0)$ is determined to be $(4.5_{-1.7}^{+2.0}(\mathrm{stat})\pm 0.4(\mathrm{syst}))\times 10^{-4}$, corresponding to an upper limit of $7.6\times 10^{-4}$ at the 90% confidence level. No significant signal of the decay $D_s^{+}\to f_1(1285)e^{+}\hat{I}{½}_e$ is observed and the upper limit on the product branching fraction is set to be $\mathcal{B}(D_s^{+}\to f_1(1285)e^{+}\hat{I}{½}_e)\cdot \mathcal{B}(f_1(1285)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\cdot )<1.7\times 10^{-4}$ at the 90% confidence level.

12 pages, 4 figures