Four-body Decay Research Articles

Search for exclusive hadronic charmless b decays at LEP

Results on exclusive hadronic charmless decays of B d 0 , B±, B s 0 and Λb from the LEP experiments ALEPH, DELPHI, L3 and OPAL are reviewed. Updated branching-ratio upper limits for several two-, three- and four-body decay modes are given as well as new limits on B u − →p\(\bar p\)π− and on B d 0 →p\(\bar p\)π+π−.

Search for exclusive charmless B meson decays with the DELPHI detector at LEP

Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given.

Study of charged hadronic four-body decays of the D0 meson

Charged hadronic four-body decays of D 0 mesons have been studied in the E687 photoproduction experiment at Fermilab. Branching ratios relative to the D 0 → K − π + π + π − decay mode for the Cabibbo-suppressed decays D 0 → π − π + π − π +, D 0 → K − K + π − π + have been measured and the first evidence of the D 0 → K − K + K − π + decay mode is reported. An analysis of the D 0 → K − K + π − π + resonance structure is also presented.

Resonant substructure in K[over ¯]πππ decays of D mesons

We determine the resonant substructure of D -> [...] decays using a five-dimensional maximum likelihood technique to extract the relative fractions and phases of the amplitudes contributing to the [...], [...], and [...] final states. We find that two-body decay modes account for about 75% of these decays. We obtain branching ratios for [...], [...], [...], [...], and [...] decay modes, as well as several three and four-body decay modes. In the case of [...] and [...], we obtain the branching ratios for all three possible isospin combinations, enabling us to extract the isospin 1/2 and 3/2 amplitudes. This allows us to eliminate the ambiguity due to phase shifts between the isospin amplitudes when comparing our results with theoretical models. We find that the isospin 3/2 amplitudes are suppressed relative to the isospin 1/2 amplitudes, confirming that an understanding of the lifetime difference of the D0 and D+ depends on an understanding of two-body hadronic decays. For the [...] decay modes, we obtain detailed information on the polarization of the [...] and [...]. This enables us to obtain information on form-factors for [...] and [...] transitions, within the context of the factorization hypothesis. Comparison of our results on [...] decays with recent results on semileptonic decays allows us to test the factorization hypothesis.

Aspects of the chirality of weak b→c transitions in the exclusive semi-leptonic decay

Abstract We consider the four-body angular decay distribution in the cascade decay B 0 → D ∗+ (→ D π)+ l − + v l . We identify the parity violating (PV) angular contributions that are to the difference H+−H− of the transverse current-induced B→D∗ helicity amplitudes. The sign of these PV contributions directly reflects the chirality of the underlying weak b→c transition. We define two asymmetry observables that are sensitive to the PV difference H+−H−. The corresponding asymmetries are calculated in a specific spectator quark model.

Weak many-body decays of the ΛC+-baryon

The generalized “hard”-meson chiral-lagrangian method, including pseudoscalar and spin-1 meson interactions with 1 2 + - baryons, is used to calulate two-, three-, and four-body non-leptonic weak decays of Λ c +. It is shown that the theoretical and experimental ratios of the decay modes are in fair agreement.

Light scalar top quark at e+e- colliders.

We examine the production and decay of a supersymmetric scalar top t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$ at ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ colliders such as TRISTAN at KEK, the Stanford Linear Collider, and LEP at CERN, based on supersymmetric models with soft breaking. Existing bounds for supersymmetric particles imply that t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$ in the energy range of these colliders would be lighter than other scalar quarks and than the top quark. We make a careful study of available t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$ decay modes in this scenario. The flavor-changing decay t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$\ensuremath{\rightarrow}c\ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{} is found to proceed through the misalignment of the scalar-quark and quark mixing matrices. If the three-body decay t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$\ensuremath{\rightarrow}${\mathrm{bl}}^{+}$\ensuremath{\nu}\ifmmode \tilde{}\else \~{}\fi{} is kinematically accessible it dominates the two-body decay. The decay t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$\ensuremath{\rightarrow}b\ensuremath{\nu}l${\ifmmode \tilde{}\else \~{}\fi{}}^{+}$ is even larger due to different chirality structure, but is likely to suffer from a large phase-space suppression. Four-body decays are negligible. The t${\ifmmode \tilde{}\else \~{}\fi{}}_{1}$ pair production cross section including the \ensuremath{\gamma} and Z contribution and the left-right mixing is presented.

Semileptonic decays of the charmed baryon [formula omitted] in the phenomenological chiral lagrangian method

The phenomelogical chiral larangian method is applied for describing the semileptonic decays of the charmed baryon ∧ + c . The partial widths are calculated for three- and four-body decays. It is shown that the Cabibbo-favored decay ∧ + c → ∧ ev dominates; the branching ratio for this decay is close to the experimental result for the inclusive decay ∧ + c → ∧ eX .

Baryon and lepton number violation in superstring models

We discuss violations of baryon and lepton number in a class of superstring models which are motivated from considerations of the E 8 × E 8 heterotic string theory. The proton undergoes four-body decays of the type p → M +ℓ 1 +ℓ 2 − v ̄ ( or v) , where M + denotes a meson and the rest are leptons. Other rare processes include μ → e γ and K + → π +e +e −. Although their rates cannot be accurately estimated, for a reasonable choice of parameters, all these processes are experimentally accessible. Neutrino masses and photino decays are also briefly discussed.

Search for scalar superpartners of the top quark

The phenomenology of top squarks is investigated in the framework of a large class of models based on spontaneously-broken local supersymmetry, in which the top quark often has a scalar superpartner lighter than m t. We find that two-body (one-loop) decays of top squarks lighter than top quarks dominate over four-body (tree-level) decays. We also focus on the changes expected in the decay patterns of the top quark given a light scalar top, and argue that the observation of top quarks decaying according to standard-model expectations would serve to rule out many models with light scalar top and light gauginos.

Heavy flavors in four-bodyZ0decay

Four-body decay of the ${Z}^{0}$ into one heavy fermion (${M}_{h}\ensuremath{\ge}50$ GeV) and three light fermions has been calculated at $O({{\ensuremath{\alpha}}_{W}}^{3})$ in the $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ theory. The expression for the decay rate was derived and numerical integration over the phase space was performed. The heavy fermion was taken to be the top quark or any of the hypothetical fourth-generation quarks and leptons. For heavy-fermion mass ${M}_{h}l{M}_{W}$, the approximation of real-intermediate-$W$ production and subsequent decay was good to only about a factor of 2.5. All branching ratios are at most \ensuremath{\sim}${10}^{\ensuremath{-}7}$ (times a possibly small Kobayashi-Maskawa factor in the fourth-generation case), and decrease with increasing ${M}_{h}$.

Gluino decays and experimental signatures

Supersymmetry could be revealed by the discovery of gluinos, the supersymmetric partners of the gluons. Previously, it has been assumed that gluinos decay entirely into q q γ (or gG̃ if a goldstino G̃ exists) where the photino γ is assumed to be the lightest supersymmetric particle. We point out that the C- violating decay g ̃ → g γ could be competitive if there is sufficient mass splitting between the scalar partners of the left- ans right-handed quarks. We also consider four-body gluino decay modes which under certain conditions could dominate, and we relax the usual assumption of massless photinos. We discuss the phenomenological implications of these new modes and indicate the effects on possible experimental signatures of supersymmetry; when the g γ mode is large it greatly improves the possibilities for detecting gluinos in both collider and beam dump experiments, perhaps even allowing detection of individual events at colliders.

ρ(770)→4πdecay in a broken-SU6×O3quark model

An attempt is made to calculate the decay rate of the rare four-body decay mode, ${\ensuremath{\eta}}^{\ensuremath{'}}(958)\ensuremath{\rightarrow}4\ensuremath{\pi}$, within the general framework of a broken-S${\mathrm{U}}_{6}$\ifmmode\times\else\texttimes\fi{}${\mathrm{O}}_{3}$ quark model of relativistically invariant coupling structures. The calculation is based on the assumption that the $4\ensuremath{\pi}$ final state is realized from the dominance of the decay by the $\ensuremath{\rho}\ensuremath{\rho}$ intermediate state, viz., ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\rho}\ensuremath{\rightarrow}(2\ensuremath{\pi})(2\ensuremath{\pi})$.

η′(958)→4πdecay in a broken-SU6×O3quark model

An attempt is made to calculate the decay rate of the rare four-body decay mode, ${\ensuremath{\eta}}^{\ensuremath{'}}(958)\ensuremath{\rightarrow}4\ensuremath{\pi}$, within the general framework of a broken-S${\mathrm{U}}_{6}$\ifmmode\times\else\texttimes\fi{}${\mathrm{O}}_{3}$ quark model of relativistically invariant coupling structures. The calculation is based on the assumption that the $4\ensuremath{\pi}$ final state is realized from the dominance of the decay by the $\ensuremath{\rho}\ensuremath{\rho}$ intermediate state, viz., ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\rho}\ensuremath{\rightarrow}(2\ensuremath{\pi})(2\ensuremath{\pi})$.

Radiative decays of theδ(980)in a vector-dominance model

A vector-dominance model is used to calculate the widths of the three- and four-body radiative decays of the $\ensuremath{\delta}(980)$.

Three-body nonleptonic and four-body semileptonicΔC=ΔSdecays of charmed hadrons

Tests of the isospin and SU(3) transformation properties of the $\ensuremath{\Delta}C=\ensuremath{\Delta}S$ current and nonleptonic interaction are given for the three-body nonleptonic and four-body semileptonic decays of a charmed hadron belonging to the 3* representation of SU(3). The relations obtained can also be used for quasi-three-body nonleptonic and quasi-four-body semileptonic decays thus covering to some extent higher multibody decays of both kinds.

Four-body semi-leptonic decay rates of charmed baryons

Four-body semi-leptonic decay rates of charmed baryons

F0→4πdecay in a relativistic quark model

Based on a relativistic version of the phenomenological couplings among hadrons in the broken SU(6) \ifmmode\times\else\texttimes\fi{} O(3) quark model developed largely by Mitra, we calculate the decay width and the corresponding branching ratio for the four-body decay process ${f}^{0}\ensuremath{\rightarrow}4\ensuremath{\pi}$. In addition, we assume that the dominant contribution to the process ${f}^{0}\ensuremath{\rightarrow}4\ensuremath{\pi}$ comes from the mechanism ${f}^{0}\ensuremath{\rightarrow}{A}_{1}\ensuremath{\pi}\ensuremath{\rightarrow}(\ensuremath{\rho}\ensuremath{\pi})\ensuremath{\pi}\ensuremath{\rightarrow}4\ensuremath{\pi}$. The model makes a very interesting prediction for the branching ratio $\frac{\ensuremath{\Gamma}({f}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}})}{\ensuremath{\Gamma}({f}^{0}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi})}$ which turns out to be 3.1%, in excellent agreement with the recent experimental value of (3.7 \ifmmode\pm\else\textpm\fi{} 0.7)% determined by Anderson et al.

Four-body semileptonic decays of hyperons

The rates of four-body semileptonic hyperon decays are calculated, using Cabibbo theory and current-algebra techniques. Observation of such decays cannot be expected until the number of observed hyperons has increased by a factor 10–100. The corrections to the pure current-algebra approach are found to be considerable.

Four-Body Semileptonic Decay of Hyperons and Algebra of Currents

A study of four-body semileptonic decay of hyperons has been made in the scheme of alge­ bra of currents assuming the Cabibbo current, the partially conserved axial-vector current and the soft pion hypotheses. The S-matrix element may be approximated by the sum of the equal­ time commutators of the relevant currents and single baryon terms. The A Y = AQ rule between the initial and final hadrons admits nine electron associated decays. Three of them are highly forbidden in our approach, the other three are associated with the induced neutral current and the rests are closely related to the three-body semileptonic decays. Finally the relative rates of those decays are estimated numerically and are expected to give further information on the structure of the weak interaction when they are studied experi­ mentally.