Observation of $D^0\to K_1(1270)^- e^+\nu_e$

TL;DR

This paper reports the first observation of the semileptonic decay $D^0 o K_1(1270)^- e^+ u_e$ with a high statistical significance, measuring its branching fraction and polarization fraction using BESIII data.

Contribution

The study provides the first measurement of the branching fraction and polarization fraction for the decay $D^0 o K_1(1270)^- e^+ u_e$, advancing understanding of charm semileptonic decays.

Findings

Decay observed with >10σ significance.

Branching fraction measured as (1.09±0.13^{+0.09}_{-0.16}±0.12)×10^{-3}.

Longitudinal polarization fraction determined to be 0.50±0.19±0.08.

Abstract

Using 2.93 fb$^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at a center-of-mass energy of 3.773 $\rm \,GeV$, the observation of the $D^0\to K_1(1270)^- e^+\nu_e$ semileptonic decay is presented. The statistical significance of the decay $D^0\to K_1(1270)^- e^+\nu_e$ is greater than $10\sigma$. The branching fraction of $D^0\to K_1(1270)^- e^+\nu_e$ is measured to be $(1.09\pm0.13^{+0.09}_{-0.16} \pm 0.12)\times10^{-3}$. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of $K_1(1270)^- \rightarrow K^-\pi^+\pi^-$. The fraction of longitudinal polarization in $D^0\to K_1(1270)^- e^+\nu_e$ is determined for the first time to be $0.50\pm0.19_{\rm stat}\pm0.08_{\rm syst}$.