Branching Fractions Of Order Research Articles

Four-lepton decays of neutral vector mesons

We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/\psi$, $\Upsilon$, $\rho^0$, $\omega,\phi$, \ldots) into four charged leptons ($2(e^+e^-)$, $2(\mu^+\mu^-)$, $2(\tau^+\tau^-)$, $e^+e^-\mu^+\mu^-$, $e^+e^-\tau^+\tau^-$, \ldots) at lowest order in QED. In contrast to the case of vector meson decay into a single pair of leptons, the lepton mass must be retained in these four-lepton decay channels to cutoff the mass singularity. Owing to more pronounced collinear enhancement, the branching fractions of vector mesons decays into $ 2(e^+e^-)$ are considerably greater than those for decays into $2(\mu^+\mu^-)$. The decay channels $J/\psi(\Upsilon)\to 2(e^+e^-), e^+e^-\mu^+\mu^-$ are predicted to have branching fractions of order $10^{-5}$, which appear to have bright observation prospect at {\tt BESIII}, {\tt Belle 2} and {\tt LHC} experiments.

Smallness of tree-dominated charmless two-body baryonicBdecay rates

The long-awaited baryonic $B$ decay ${\overline{B}}^{0}\ensuremath{\rightarrow}p\overline{p}$ was recently observed by LHCb with a branching fraction of order $1{0}^{\ensuremath{-}8}$. All the earlier model predictions are too large compared with experiment. In this work, we point out that for a given tree operator ${O}_{i}$, the contribution from its Fiertz transformed operator, an effect often missed in the literature, tends to cancel the internal $W$-emission amplitude induced from ${O}_{i}$. The wave function of low-lying baryons is symmetric in momenta and the quark flavor with the same chirality but antisymmetric in color indices. Using these symmetry properties and the chiral structure of weak interactions, we find that half of the Feynman diagrams responsible for internal $W$ emission cancel. Since this feature holds in the charmless modes but not in the charmful ones, we advocate that the partial cancellation accounts for the smallness of the tree-dominated charmless two-body baryonic $B$ decays. This also explains why most previous model calculations predicted too large rates as the above consideration was not taken into account. Finally, we emphasize that, contrary to the claim in the literature, the internal $W$-emission tree amplitude should be proportional to the Wilson coefficient ${c}_{1}+{c}_{2}$ rather than ${c}_{1}\ensuremath{-}{c}_{2}$.

Exclusive decay ofΥintoJ/ψ+χc0,1,2

We study the $\Upsilon$ exclusive decay into double charmonium, specifically, the $S$-wave charmonium $ J/\psi$ plus the $P$-wave charmonium $\chi_{c0,1,2}$ in the NRQCD factorization framework. Three distinct decay mechanisms, i.e., the strong, electromagnetic and radiative decay channels are included and their interference effects are investigated. The decay processes $\Upsilon(1S,2S,3S)\to J/\psi+\chi_{c1,0}$ are predicted to have the branching fractions of order $10^{-6}$, which should be observed in the prospective Super $B$ factory.

Flavor-changing decays of fourth-generation quarkonium.

We evaluate the flavor-changing neutral-current decays {ital S}({ital v{bar v}}){r arrow}{ital c{bar t}},{ital t{bar c}},{ital a{bar t}},{ital t{bar a}} of the {ital S}-wave quarkonium states formed from the {ital Q}={minus}1/3 charge {ital v} quark of a fourth-generation quark doublet ({ital a},{ital v}). Under favorable mass and mixing conditions these decay modes could occur with branching fractions of order 1%.

Higgs-boson production via pseudoscalar toponium.

The eta/sub t/(/sup 1/S/sub 0/) toponium state may decay to a neutral Higgs boson H and two gluons, with a branching fraction of order G/sub F/M/sub eta//sub =//sup 2/. Also the eta/sub t/ and H can be produced via the gluon-fusion subprocess gg..-->..eta/sub t/H. We evaluate the rates for these processes at hadron colliders and discuss the possibility for detection via H..-->..tau/sup +/tau/sup -/ decays with these mechanisms.

Technipionium bound state formation and decays

Color octet technipion pairs bound together by the strong interaction could be produced at hadron colliders via gluon-gluon fusion. They would decay to W +W −, γγ, and Zγ with branching fractions of order (0.1–0.3)%. These signals are easily detectable at multi-TeV hadron supercolliders.

Gluon enhancements in charmed-meson decays

We address tests of nonspectator diagrams in charmed-meson decays. In particular, we explore the consequences of a model in which such diagrams are enhanced by the emission of a single gluon. For a lifetime ratio tau(D/sup +/)/tau(D/sup 0/)=5, we predict (i) tau(F/sup +/)/tau(D/sup +/) approx. = 0.6, (ii) an enhanced ..delta..S=0 rate for D/sup +/, (iii) a substantial multipion branching fraction for the F/sup +/, (iv) an F/sup +/ ..-->.. tau/sup +/..nu.. branching fraction of order 10 --20%, and (v) restrictive bounds on the D/sup 0/ ..-->.. K-bar/sup 0/..pi../sup 0/ mode.