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Register a new user$Delta L=2$ hyperon semileptonic decays
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We compute the rates of semileptonic B_A to B_Bl^-l^- (l=e or mu) hyperon transitions in a model where intermediate states involve loops of baryons and a Majorana neutrino. These rates turn out to be well below present experimental bounds and other theoretical estimates. From the experimental upper limit on the Xi^- to pmu^-mu^- decay, we derive the bound <m_{mu mu}> < 22 TeV for the effective Majorana mass of the muon neutrino. Also, an estimate of background contributions for these decays due to the allowed B_A to B_Bl^-l^-bar{ u}bar{ u} decays are provided.
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The study of neutrinoless double beta decays of nuclei and hyperons require the calculation of hadronic matrix elements of local four-quark operators that change the total charge by two units Delta Q=2 . Using a low energy effective Lagrangian that induces these transitions, we compute these hadronic matrix elements in the framework of the MIT bag model. As an illustrative example we evaluate the amplitude and transition rate of Sigma- -> p e- e-, a decay process that violates lepton number by two units (Delta L=2). The relevant matrix element is evaluated without assuming the usual factorization approximation of the four-quark operators and the results obtained in both approaches are compared.
A sensitive search for the rare decays Omega^- to Lambda pi^- and Xi^0 to p pi^- has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |Delta S| = 2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Omega^- to Lambda pi^-)< 2.9 x 10^{-6} and B(Xi^0 to p pi^-)< 8.2 x 10^{-6}, both at 90% confidence level.
We analyse the semileptonic decay D+ -> K- pi+ l+ nu(l) using an effective Lagrangian developed previously to describe the decays D -> P l nu(l) and D -> V l nu(l). Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no new parameters the model correctly reproduces the measured ratio Gamma(nres)/Gamma(nres + res). We also present useful nonresonant decay distributions. Finally, a similar model, but with a modified current which satisfies the soft pion theorems at the expense of introducing another parameter, is analyzed and the results of the models are compared.
In the SUSY SO(10) GUT context, we study the exclusive processes $B to K^{(*)} l^+l^-(l=mu,tau)$. Using the Wilson coefficients of relevant operators including the new operators $Q_{1,2}^{(prime)}$ which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like, the invariant mass spectrum (IMS), lepton pair forward backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients $C_{Q_{1,2}}^prime$, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA, $dL/dhat{s}$, and $dT/dhat{s}$ of $B to K^{(*)} tau^+ tau^-$ decay, which are expected to be measured in B factories, and the average of the normal polarization $dN/dhat{s}$ can reach several percent for $B to K mu^+ mu^-$ and it is 0.05 or so for $Bto K tau^+tau^-$, which could be measured in the future super B factories and provide a useful information to probe new physics and discriminate different models.
We find evidence for the semileptonic baryonic decay $B^-to pbar pell^-bar u_ell$ ($ell=e,mu$), based on a data sample of 772 million $Bbar B$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy electron-positron collider. A neural-network based hadronic $B$-meson tagging method is used in this study. The branching fraction of $B^-to pbar pell^-bar u_ell$ is measured to be $(5.8^{+2.4}_{-2.1}textrm{(stat.)}pm 0.9textrm{(syst.)})times 10^{-6}$ with a significance of 3.2$sigma$, where lepton universality is assumed. We also estimate the corresponding upper limit: $mathcal{B}(B^-to pbar pell^-bar u_ell) < 9.6times 10^{-6}$ at the 90% confidence level. This measurement helps constrain the baryonic transition form factor in B decays.
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