Session D12: Rare B Decays, B-Baryon

Saturday, February 13, 2010

A search is performed for the decay $B \rightarrow \textrm{baryon } \textrm{lepton}$, where the baryon is either a $\Lambda_c^+$ or $\Lambda^0$ and the lepton is a muon or electron. This decay would violate baryon (B) and lepton (L) number individually. In some of the decays in which we search, the difference (B-L) is conserved. The $B-L$-conserving process is generally interpreted as being mediated by a boson that carries both color and lepton number and is fractionally charged. This boson is a signature of some unification theories. The flavor/generation dependence of this type of interaction can be constrained by a comprehensive search for decays involving different flavors of quarks and leptons. At the SLAC National Accelerator Laboratory, the PEP-II storage rings provided $e^+/e^-$ beams from 1999-2008, during which time the {\sl B{\scriptsize A}B{\scriptsize AR}} experiment collected 429 fb$^{-1}$ of data at the $\Upsilon(4S)$ resonance giving this analysis access to 1 billion $B$ mesons. In the event of a null result, upper limits on the $B$ branching fractions for these processes will be calculated in order to provide experimental constraints. The status of the search will be presented.   

Saturday, February 13, 2010

We present a search for the decay $B\rightarrow\nu\overline{\nu}(\gamma)$ in $\Upsilon (4S)\rightarrow B\kern 0.18em\overline{\kern -0.18em B}$ decays recorded with the {\sl B{\scriptsize A}B{\scriptsize AR}} detector at the PEP-II asymmetric-energy $B$ factory at SLAC. The Standard Model predictions for the $B\rightarrow\nu\overline{\nu}(\gamma)$ branching fractions are far from the current experimental sensitivities, but many New Physics Models predict significant enhancements. A sample of events in which one $B$ is reconstructed in $B^{0}\rightarrow D(^{*})l\nu$ modes is selected, and in the recoil a search for a $B$ decaying to purely invisible final states or to a photon plus missing energy is performed. In order to reject background a number of kinematic and shape selection criteria are used. Features of the signal signature are exploited by imposing constraints on signal variables such as track multiplicity, neutral energy and missing momentum. We describe the search techniques and provide the most recent results from {\sl B{\scriptsize A}B{\scriptsize AR}}.   

Saturday, February 13, 2010

We present an analysis of charmless semileptonic $B$-meson decays recorded with the {\sl B{\scriptsize A}B{\scriptsize AR}} detector at the $\Upsilon(4S)$ resonance. We measure branching fractions for the exclusive modes $B \rightarrow (\pi/\rho/\omega) \ell \nu$. We compare the measured distribution in $q^2$, the momentum-transfer squared, with theoretical predictions based on lattice QCD, light-cone sum rules, and quark model form factor calculations. We also extract the CKM matrix element $|V_{ub}|$ from $B \rightarrow \pi\ell\nu$ decays.   

Saturday, February 13, 2010

We report results on the measurement of the forward-backward asymmetry ($A_{\rm FB}$) in $B\to K^{(*)}\mu\mu$. $A_{\rm FB}$ may imply new physics beyond the standard model via the loop structure in the decay. The data set is collected with the CDF II detector using $p\bar{p}$ collisions produced at the Fermilab Tevatron. $A_{\rm FB}$ is extracted from a muon angular distribution in dimuon restframe. We also present a search result for $B_s^0\to \phi\mu\mu$ that is not observed so far.   

Saturday, February 13, 2010

In 2006 CDF Collaboration reported a first observation of bottom baryon states $\Sigma_{b}$. Based on $\sim$~5.0~fb$^{-1}$ of CDF data we present a high statistics measurements of strongly decaying b-baryons based on a data sample of fully reconstructed $\Lambda_{b}$ decays collected by CDF~II detector at $\sqrt{s} = 1.96$~TeV in several trigger paths. The confirmation of the discovery and the first independent mass and widths measurements of all four states $\Sigma_{b}^{(*)+}$ and $\Sigma_{b}^{(*)-}$ will be presented.