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Register a new userObservation of the Semileptonic $D^+$ Transition into an Axial-Vector Meson $bar K_1(1270)^0$
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By analyzing a 2.93~$rm fb^{-1}$ data sample of $e^+e^-$ collisions, recorded at a center-of-mass energy of 3.773 $rm ,GeV$ 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 $D^{+} rightarrow {bar{K}}_{1}(1270)^{0}e^{+} u_{e}$ decay is observed for the first time with a statistical significance greater than $10sigma$. Its decay branching fraction is determined to be ${mathcal B}[D^+to bar K_1(1270)^0 e^+ u_e]=(2.30pm0.26pm 0.18 pm 0.25)times10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${bar{K}}_{1}(1270)^{0} rightarrow K^{-} pi^{+} pi^{0}$.
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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 $D^0to K_1(1270)^- e^+ u_e$ semileptonic decay is presented. The statistical significance of the decay $D^0to K_1(1270)^- e^+ u_e$ is greater than $10sigma$. The branching fraction of $D^0to K_1(1270)^- e^+ u_e$ is measured to be $(1.09pm0.13^{+0.09}_{-0.16} pm 0.12)times10^{-3}$. 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 $D^0to K_1(1270)^- e^+ u_e$ is determined for the first time to be $0.50pm0.19_{rm stat}pm0.08_{rm syst}$.
The COMPASS collaboration at CERN has measured diffractive dissociation of 190 GeV/$c$ pions into the $pi^-pi^-pi^+$ final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of $3pi$ mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow $J^{PC} = 1^{++}$ signal is observed in the $f_0(980),pi$ channel. We present a resonance-model study of a subset of the spin-density matrix selecting $3pi$ states with $J^{PC} = 2^{++}$ and $4^{++}$ decaying into $rho(770),pi$ and with $J^{PC} = 1^{++}$ decaying into $f_0(980),pi$. We identify a new $a_1$ meson with mass $(1414^{+15}_{-13})$ MeV/$c^2$ and width $(153^{+8}_{-23})$ MeV/$c^2$. Within the final states investigated in our analysis, we observe the new $a_1(1420)$ decaying only into $f_0(980),pi$, suggesting its exotic nature.
Using data collected by the fixed target Fermilab experiment FOCUS, we present several first measurements for the semileptonic decay $D^0 to bar{K}^0pi^-mu^+ u$. Using a model that includes a $bar{K}^0 pi^-$ S-wave component, we measure the form factor ratios to be r_v= 1.706+-0.677+-0.342 and r_2= 0.912+-0.370+-0.104 and the S-wave amplitude to be A=0.347+-0.222+-0.053 GeV^-1. Finally, we measure the vector semileptonic branching ratio $frac{Gamma(D^0 to K^{*}(892){-}mu^+ u)}{Gamma(D^0 to bar{K}^0pi^-pi^+)}= 0.337+-0.034+-0.013.
We observe $D^0-bar{D}^0$ mixing in the decay $D^0rightarrow K^+pi^-$ using a data sample of integrated luminosity 976 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We measure the mixing parameters ${x}^2 = (0.09pm0.22)times 10^{-3}$ and $y = (4.6pm3.4)times 10^{-3}$ and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates $R_D = (3.53pm0.13)times 10^{-3}$, where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.
Motivated by the experimental measurements of $D^0$ radiative decay modes we have proposed a model to study the $D^0to bar{K}^{*0}gamma$ decay, by establishing a link with $D^0to bar{K}^{*0}V$ $(V=rho^0,, omega)$ decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for $Vgamma$ conversion. As a result, we have found the branching ratio $mathcal{B}[D^0to bar{K}^{*0}gamma] =(1.55 - 3.44)times 10^{-4}$, which is in fair agreement with the experimental values reported by Belle and Babar collaborations.
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