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Register a new userMeasurement of the $D^0 to pi^-e^+ u$ branching fraction, form factor and implications for $V_{ub}$
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Arantza Oyanguren
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In this talk results of the study of the $D^0 to pi^- e^+ u$ decay channel, recorded by the BaBar detector at the c.m. energy close to 10.6 GeV, are reported. The branching fraction of this channel is measured relative to the $D^0 to K^- pi^+$ decay. The hadronic form factor, $f_{+,D}^{pi}(q^2)$, function of $q^2$, the four momentum transfer squared between the $D$ and the $pi$ mesons, is compared to various theoretical predictions, and the normalization $V_{cd} times f_{+,D}^{pi}(q^2=0)$ is extracted from a fit to data. Results are compared with Lattice QCD calculations. A new multipole model is applied which makes use of present information of resonant states contributing to the form factor. With the understanding of the $f_{+,D}^{pi}(q^2)$ form factor, and provided the relation between the $D^0 to pi^- e^+ u$ and $B^0 to pi^- e^+ u$ decay widths at the same pion energy, the CKM matrix element $V_{ub}$ is determined and compared to recent measurements. This method of extracting $V_{ub}$ will become competitive with new Lattice QCD calculations of the ratio of form factors.
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A measurement of the vector to pseudoscalar conversion decay $phi to pi^0 e^+e^-$ with the KLOE experiment is presented. A sample of $sim 9500$ signal events was selected from a data set of 1.7 fb$^{-1}$ of $e^+e^-$ collisions at $sqrt{s} sim m_{phi}$ collected at the DA$Phi$NE $e^+e^-$ collider. These events were used to obtain the first measurement of the transition form factor $| F_{phi pi^0}(q^2) |$ and a new measurement of the branching ratio of the decay: $rm{BR},(phi to pi^0 e^+e^-) = (,1.35 pm 0.05^{,,+0.05}_{,,-0.10},) times 10 ^{-5}$. The result improves significantly on previous measurements and is in agreement with theoretical predictions.
Based on a sample of 500 million $e^+e^- to cbar c$ events recorded by the BaBar detector at c.m. energies of close to 10.6 GeV, we report on a study of the decay $D^0 to pi^- e^+ u_e$. We measure the ratio of branching fractions $R_D = {cal B}(D^0 to pi^- e^+ u_e)/{cal B}(D^0 to K^- pi^+) = 0.0713 pm 0.0017_{stat.} pm 0.0024_{syst.}$, and use the present world average for ${cal B}(D^0 to K^- pi^+)$ to obtain ${cal B}(D^0 to pi^- e^+ u_e) = (2.770 pm 0.068_{{rm stat.}} pm 0.092_{{rm syst.}} pm 0.037_{{rm ext.}})times 10^{-3}$ where the third error accounts for the uncertainty on the branching fraction for the reference channel. The measured dependence of the differential branching fraction on $q^2$, the four-momentum transfer squared between the $D$ and the $pi$ meson, is compared to various theoretical predictions for the hadronic form factor, $f_{+,D}^{pi}(q^2)$, and the normalization $|V_{cd}| times f_{+,D}^{pi}(q^2=0)=0.1374pm0.0038_{{rm stat.}} pm0.0022_{{rm syst.}} pm0.0009_{{rm ext.}}$ is extracted from a fit to data. Using the most recent LQCD prediction of $f_{+,D}^{pi}(q^2=0)=0.666 pm 0.029$, we obtain $|V_{cd}|=0.206 pm 0.007_{rm exp.} pm 0.009_{rm LQCD}$. Assuming instead, $|V_{cd}|=|V_{us}|=0.2252 pm 0.0009$, we obtain $f_{+,D}^{pi}(q^2=0)=0.610 pm 0.020_{rm exp.} pm 0.005_{rm ext.}$. The $q^2$ dependence of $f_{+,D}^{pi}(q^2)$ is compared to a variety of multi-pole parameterizations. This information is applied to $B^0 to pi^- e^+ u_e$ decays and, combined with an earlier $B^0 to pi^- e^+ u_e$ measurement by BaBar, is used to derive estimates of $|V_{ub}|$.
Using $2.92$ fb$^{-1}$ of electron-positron annihilation data collected at $sqrt{s} = 3.773$~GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process $D^0togammagamma$ using a double-tag technique. We find no signal and set an upper limit at $90%$ confidence level for the branching fraction of $B(D^0togammagamma) < 3.8times10^{-6}$. We also investigate $D^0$-meson decay into two neutral pions, obtaining a branching fraction of $B(D^0topi^0pi^0) = (8.24pm0.21(text{stat.})pm0.30(text{syst.}))times10^{-4}$, the most precise measurement to date and consistent with the current world average
By studying the invariant-mass distribution of the $e^+e^-$ in conversion decays, it is possible to learn more about mesons structure and underlying quark dynamics. At KLOE, the study of the $phi to pi^0 e^+e^-$ process is currently going to be finalized. At present, about 9000 events have been selected from a data sample of 1.7 fb$^{-1}$ from 2004/2005 data taking campaign. A very good agreement between data and Monte Carlo distributions has been achieved for all interesting kinematical variables. A preliminary invariant-mass spectrum of $e^{+}e^{-}$ is presented.
We report the results of a study of the exclusive charmless semileptonic decays, B^0 --> pi^- l^+ nu, B^+ --> pi^0 l^+ nu, B^+ --> omega l^+ nu, B^+ --> eta l^+ nu and B^+ --> eta^ l^+ nu, (l = e or mu) undertaken with approximately 462x10^6 Bbar{B} pairs collected at the Upsilon(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q^2, the square of the momentum transferred to the lepton-neutrino pair, for B^0 --> pi^- l^+ nu, B^+ --> pi^0 l^+ nu, B^+ --> omega l^+ nu and B^+ --> eta l^+ nu. From these distributions, we extract the form-factor shapes f_+(q^2) and the total branching fractions BF(B^0 --> pi^- l^+ nu) = (1.45 +/- 0.04_{stat} +/- 0.06_{syst})x10^-4 (combined pi^- and pi^0 decay channels assuming isospin symmetry), BF(B^+ --> omega l^+ nu) = (1.19 +/- 0.16_{stat} +/- 0.09_{syst})x10^-4 and BF(B^+ --> eta l^+ nu) = (0.38 +/- 0.05_{stat} +/- 0.05_{syst})x10^-4. We also measure BF(B^+ --> eta^ l^+ nu) = (0.24 +/- 0.08_{stat} +/- 0.03_{syst})x10^-4. We obtain values for the magnitude of the CKM matrix element V_{ub} by direct comparison with three different QCD calculations in restricted q^2 ranges of B --> pi l^+ nu decays. From a simultaneous fit to the experimental data over the full q^2 range and the FNAL/MILC lattice QCD predictions, we obtain |V_{ub}| = (3.25 +/- 0.31)x10^-3, where the error is the combined experimental and theoretical uncertainty.
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