Session X9: Charm and B Physics IV

Measurement of double-charmonium production in $e^+e^-$ annihilation around $\sqrt{s} = 10.58$~GeV at {\sc BaBar}

Prompt production of $J/\psi$ or $\psi(2S)$ in association with a second charmonium state has been observed by both the BaBar and Belle experiments in $e^+e^-$ annihilation around $\sqrt{s} = 10.58$~GeV. These processes provide an opportunity to study both perturbative and non-perturbative effects in QCD and to search for new charmonium states recoiling against the reconstructed $J/\psi$ or $\psi(2S)$. I will present a study of such events using the full BaBar dataset, where the $J/\psi$ and $\psi(2S)$ are reconstructed via the decays $J/\psi \to \ell^+\ell^-$, $\psi(2S) \to J/\psi \pi^+\pi^-$, and $\psi(2S)\to \ell^+\ell^-$.   

Search for 4-lepton $B$-decay final states at {\sc BaBar}

In the Standard Model, the decay of $B$ mesons into a final state of four leptons is highly suppressed and too rare to be observed. Recently, whole new sectors of gauge bosons have been postulated in order to explain how dark matter might interact with itself and with particles in the Standard Model. A class of these models predicts that four-lepton final states of $B$-meson decay may be observable. We present a search for such final states using 471 million B/anti-B meson pairs produced at the PEP-II/{\sc BaBar} $B$ factory.   

Updated search for $B_{s(d)}\rightarrow\mu^+\mu^-$ decays at CDF

Rare $B_{s(d)}\rightarrow\mu^+\mu^-$ decays are considered among the most powerful probes of new physics. The CDF collaboration reports the latest result based on an integrated luminosity of 6.9 $\textnormal{fb}^{-1}$. More than doubled statistics with respect to the previous iteration and several analysis improvement provide results that are the most sensitive from a single-experiment to date.   

Measurement of the branching fraction of $\Upsilon(4S) \to B^0 \bar B^0$ at {\sc BaBar}

Based on a data sample of 476 million $B\bar B$ pairs collected at the $\Upsilon(4S)$ resonance with the {\sc BaBar} detector at the PEP-II asymmetric-energy $B$-Factory at the SLAC National Accelerator Laboratory, we conduct a direct, model-independent measurement of the branching fraction of the $\Upsilon(4S)$ decay to a $B^0 \bar B^0$ pair. The $B$ mesons are partially reconstructed in the decay $\bar B^0 \to D^{*+} \ell^- \bar\nu_\ell$. This measurement is important for normalizing many $B$-decay branching fractions.   

Estimation of Low Energy Constants

We assess results from Heavy Quark Effective Theory using Bayesian Analysis to predict parameters. Bayesian analysis is especially effective because it incorporates prior information into models. Thus we seek posterior distributions that include our restrictions on the parameters. These parameters, called Low Energy Constants (LECs), occur in effective theories and can only be set by inference. We hypothesize that this analysis improves the estimates for LECs for D meson decay widths. These LECs appear not only in these expressions, but also in other calculations containing D mesons. This, along with the LECs' model-independence, means that our estimates can be used in all expressions involving D mesons. Therefore, the more accurately our analysis predicts the LECs, the more accurate the physical expressions containing these constants will become. We study increasingly complex effective theories by modeling with Markov Chains and the software BUGS (Bayesian inference Using Gibbs Sampling). Afterwards, we evaluate the rates of convergence of the various parameters by introducing slight modifications into the BUGS model. We report estimates for the most common LECs and analyze their reliability.   

Determination of HQET Low Energy Constants in D and B Meson Decays

We examine the low energy constants in heavy quark effective theories to different orders in power counting as relate to the decays of positive- and negative-parity heavy mesons. We consider strong decays to order $Q^{2}$ and $Q^{3}$ separately, as well as electromagnetic decays to the same orders. Parameters otherwise suppressed by the charm quark mass are included. Decay widths are compared to experimental data using Bayesian inference techniques to determine the low energy constants.