Observation of the Semileptonic $D^{+}$ Transition into an Axial-Vector Meson ${\bar{K}}_1(1270{)}^0$

Abstract

By analyzing a 2.93~$\mathrm{f}{\mathrm{b}}^{-1}$ data sample of $e^{+}{e}^{-}$ collisions, recorded at a center-of-mass energy of 3.773 $\mathrm{GeV}$ with the BESIII detector operated at the BEPCII collider, we have searched for the semileptonic $D^{+}$ transition into the axial-vector meson ${\bar{K}}_1(1270{)}^0$. The $D^{+}\to {\bar{K}}_1(1270{)}^0{e}^{+}{\nu }_e$ decay is observed for the first time with a statistical significance greater than $10\sigma$. Its decay branching fraction is determined to be $\mathcal{B}[D^{+}\to {\bar{K}}_1(1270{)}^0{e}^{+}{\nu }_e]=(2.30\pm 0.26\pm 0.18\pm 0.25)\times 10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${\bar{K}}_1(1270{)}^0\to K^{-}{\pi }^{+}{\pi }^0$.

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• Recent Progress in Leptonic and Semileptonic Decays of Charmed Hadrons
• Observation of $D^{+}\to \eta \eta {\pi }^{+}$ and improved measurement of $D^{0(+)}\to \eta {\pi }^{+}{\pi }^{-(0)}$
• First Observation of $D^{+}\to \eta {\mu }^{+}{\nu }_{\mu }$ and Measurement of its Decay Dynamics
• Observation of the semi-muonic decay $D^{+}\to \omega {\mu }^{+}{\nu }_{\mu }$
• Novel method to reliably determine the photon helicity in $b\to s\gamma$
• Observation of $D^0\to K_1(1270{)}^{-}{e}^{+}{\nu }_e$
• Search for the semileptonic decay $D^{0(+)}\to b_1(1235{)}^{-(0)}{e}^{+}{\nu }_e$
• Observation of the Doubly Cabibbo-Suppressed Decay $D^{+}\to K^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ and Evidence for $D^{+}\to K^{+}\omega$
• Determination of the absolute branching fractions of $D^0\to K^{-}{e}^{+}{\nu }_e$ and $D^{+}\to {\bar{K}}^0{e}^{+}{\nu }_e$
• Observation of the Decay $D^0\to {\rho }^{-}{\mu }^{+}{\nu }_{\mu }$
• Measurements of the absolute branching fractions of $D^{0(+)}\to K\bar{K}\pi \pi$ decays
• Up-down Asymmetries and Angular Distributions in $D\to K_1(\to K\pi \pi ){\ell }^{+}{\nu }_{\ell }$
• Test of lepton universality and measurement of the form factors of $D^0\to K^{\ast }(892{)}^{-}{\mu }^{+}{\nu }_{\mu }$
• Observation of $D^{0(+)}\to K_S^0{\pi }^{0(+)}\omega$ and improved measurement of $D^0\to K^{-}{\pi }^{+}\omega$
• Exclusive semileptonic decays of $D$ and $D_s$ mesons into orbitally and radially excited states of strange and light mesons
• First Measurement of the Decay Dynamics in the Semileptonic Transition of the $D^{+(0)}$ into the Axial-vector Meson ${\bar{K}}_1(1270)$
• Observation of $D\to {\bar{K}}_1(1270){\mu }^{+}{\nu }_{\mu }$ and test of lepton flavor universality with $D\to {\bar{K}}_1(1270){\ell }^{+}{\nu }_{\ell }$
• A proposal to the '$\frac{1}{2}$ vs. $\frac{3}{2}$ puzzle'