First evidence for $D_s^+ \to f_1(1420) e^+\nu_e$ and search for $D_s^+ \to f_1(1285) e^+\nu_e$

TL;DR

This paper reports the first evidence for the semileptonic decay $D_s^+ o f_1(1420) e^+ u_e$ and sets upper limits for the decay $D_s^+ o f_1(1285) e^+ u_e$, using data from the BESIII detector.

Contribution

First experimental search for these specific semileptonic decays of $D_s^+$ mesons, providing evidence for one decay mode and limits for the other.

Findings

Evidence for $D_s^+ o f_1(1420) e^+ u_e$ with 3.4$\sigma$ significance.

Product branching fraction for $D_s^+ o f_1(1420) e^+ u_e$ measured as $(4.5^{+2.0}_{-1.7} ext{(stat)} \pm 0.4 ext{(syst)}) imes 10^{-4}$.

Upper limit for $D_s^+ o f_1(1285) e^+ u_e$ set at $1.7 imes 10^{-4}$ at 90 ext{% CL}.

Abstract

Using $e^+e^-$ collision data corresponding to an integrated luminosity of 7.33~${\rm fb^{-1}}$ recorded by the BESIII detector at center-of-mass energies between 4.128 and 4.226~${\rm GeV}$, we present the first search for the semileptonic decays $D^+_s\to\ f_1(1420)e^+\nu_e$ and $D^+_s\to\ f_1(1285)e^+\nu_e$. The first evidence for the decay $D^+_s\to\ f_1(1420)e^+\nu_e$ is found with a statistical significance of 3.4$\sigma$, and its product branching fraction $\mathcal{B}(D^+_s\to\ f_1(1420)e^+\nu_e)\cdot\mathcal{B}(f_1(1420)\to\ K^+K^-\pi^0)$ is determined to be $\rm (4.5^{+2.0}_{-1.7}(stat) \pm0.4(syst)) \times 10^{-4} $, corresponding to an upper limit of $7.6 \times10^{-4}$ at the 90% confidence level. No significant signal of the decay $D^+_s\to\ f_1(1285)e^+\nu_e$ is observed and the upper limit on the product branching fraction is set to be $\mathcal{B}(D^+_s\to\ f_1(1285)e^+\nu_e)\cdot\mathcal{B}(f_1(1285)\to\ \pi^+\pi^-\eta) < 1.7\times10^{-4}$ at the 90% confidence level.