Study of \tau decays involving kaons, spectral functions and determination of the strange quark mass

All ALEPH measurements of branching ratios of decays involving kaons are summarized including a combination of results obtained with and detection. The decay dynamics are studied, leading to the determination of contributions from vector and , and axial-vector and resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the mode is compared with the corresponding cross section for low energy annihilation, yielding an axial-vector fraction of for this mode. The branching ratio for decay into all strange final states is determined to be . The measured mass spectra of the strange decay modes are exploited to derive the spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result MeV/. The evolution down to 1 GeV gives . Received: 24 February 1999 / Published online: 14 October 1999     

Isospin restrictions on charge distributions in charmed-particle decays

The isospin properties of the semileptonic and non-leptonic charm-changing weak interactions lead to restrictions on the branching ratios of the different charge states that can occur in multi-particle decays of charmed particles. Upper and lower bounds imposed by isospin invariance on these ratios, and on the average number of charged decay products, are calculated for various charmed-particle decay modes. Simultaneous bounds on the branching ratios of two different charge distributions in the same decay mode, or in isospin-related decay modes, are presented. Branching ratios are also calculated under the statistical postulate that all the allowed invariant isospin channels contribute equally and incoherently in each decay mode.     

Decay properties of the key resonant states in8Li(α, n)11B for primordial nucleosynthesis

The particle decay property of the key resonant states in the reaction⁸Li(,n)¹¹B for the inhomogeneous big bang models was studied experimentally. The sum of the branching ratios of the 10.572 MeV state for the neutron decays to the excited states in¹¹B is as large as for the ground state, indicating that the neutron decays to excited states are crucial and enhance the reaction rate for heavy element synthesis considerably.     

Observation of doubly-charmed B decays at LEP

A search for doubly-charmed B decays with both charmed mesons reconstructed is performed, using about 3.8 million hadronic Z decays recorded with the ALEPH detector at LEP. A clear signal is observed in the channels and (where D can be either a D, a D or a D), providing the first direct evidence for doubly-charmed B decays involving no production. Evidence for associated and production in the decays is also presented and some candidates for completely reconstructed decays , and are observed. Furthermore, candidates for the two-body Cabibbo suppressed decays and are also observed. Measurements of the corresponding branching fractions are extracted. Received: 6 March 1998 / Published online: 23 June 1998     

Study of tau decays to six pions and a neutrino

The tau decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(tau(-)-->2pi(-)pi(+)3pi(0)nu(tau)) = (2.2+/-0.3+/-0.4)x10(-4) and B(tau(-)-->3pi(-)2pi(+)pi(0)nu(tau)) = (1.7+/-0.2+/-0.2)x10(-4). A search for substructure in these decays shows that they are saturated by intermediate states with eta or omega mesons. We present the first observation of the decay tau(-)-->2pi(-)pi(+)omega(nu)tau and the branching fraction is measured to be (1.2+/-0.2+/-0.1)x10(-4). The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.     

Measurement of the {\rm\bf B_{\bf d}^{\bf 0}- {\bf \bar{B}}_{\bf d}^{\bf 0}} oscillation frequency

Time-dependent mixing is studied using about two million hadronic Z decays registered by L3 in 1994 and 1995. For this study three techniques are used. Tagging of the b-quark charge at decay time is performed by identifying leptons from semileptonic B decays. The flavour of the b quark at production time is determined from the charge of the lepton in the opposite hemisphere or by using a jet-charge technique. The proper time of the B-particle decay is obtained by reconstructing the production and decay vertices or by a measurement of the lepton impact parameter. The combined result for the frequency of meson oscillations is Received: 20 February 1998 / Revised version: 23 March 1998 / Published online: 12 August 1998     

Spin correlations in production and decay of charginos

We study the production of charginos with polarized beams and the subsequent decays and , including the complete spin correlations between production and decay. Analytical formulae are presented for the joint spin-density matrix of the charginos, for the chargino decay matrix and for the differential cross section of the combined processes of production and decays. We present numerical results for pair production of the lighter chargino with unpolarized beams and the leptonic decay of into the lightest neutralino . The lepton angular distribution and the forward-backward asymmetry are studied in four representative scenarios for GeV and GeV. Received: 28 April 1998 / Revised version: 18 June 1998 / Published online: 8 September 1998     

The rare K decays and Z^0 penguin contributions in the topcolor-assisted technicolor models

We calculate the new contributions to the rare decays K, and from new Z penguin and box diagrams induced by the unit-charged scalars appearing in the topcolor-assisted technicolor (TC2) models. We find that: (a) the unit-charged top-pion and b-pion can provide large contributions to the rare K decays if they are relatively light; (b) the size of the mixing elements () is strongly constrained by the data of B meson mixing: for and GeV; (c) the enhancements to the branching ratios of rare K decays from new scalars can be as large as one order of magnitude; (d) there is a strong cancellation between the short- and the long-distance dispersive part of the decay , the constraint on the new short-distance part from this decay mode is thus not strong; (e) the typical TC2 model under study is generally consistent with the available rare K-decay data. Received: 24 November 1998 / Revised version: 16 February 1999 / Published online: 15 July 1999     

Observation of Upsilon(3S)-->tau+tau- and tests of lepton universality in Upsilon decays

Using data collected with the CLEO III detector at the CESR e+e- collider, we report on a first observation of the decay Upsilon(3S)-->tau+tau-, and precisely measure the ratio of branching fractions of Upsilon(nS), n=1, 2, 3, to tau+tau- and mu+mu- final states, finding agreement with expectations from lepton universality. We derive absolute branching fractions for these decays, and also set a limit on the influence of a low mass CP-odd Higgs boson in the decay of the Upsilon(1S).     

Search for B0 decays to invisible final states and to nunugamma

We establish upper limits on branching fractions for B0 decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for B0 decays to nunugamma. Within the standard model, these decays have branching fractions that are below current experimental sensitivity, but various models of physics beyond the standard model predict significant contributions from these channels. Using 88.5 x 10(6) BB pairs collected at the Upsilon(4S) resonance by the BABAR experiment at the PEP-II e(+)e- storage ring at the Stanford Linear Accelerator Center, we establish upper limits at the 90% confidence level of 22 x 10(-5) for the branching fraction of B0-->invisible and 4.7 x 10(-5) for the branching fraction of B0-->nunugamma.     

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → q?v_? + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.     

B decays to baryons

From inclusive measurements, it is known that about 7% of all B mesons decay into final states with baryons. In these decays, some striking features become visible compared to mesonic decays. The largest branching fractions come with quite moderate multiplicities of 3?C4 hadrons. We note that two-body decays to baryons are suppressed relative to three- and four-body decays. In most of these analyses, the invariant baryon?Cantibaryon mass shows an enhancement near the threshold. We propose a phenomenological interpretation of this quite common feature of hadronization to baryons.     

Charmless decays B \to{\mathrm{PP}}, {\mathrm{PV}}, and the effects of new strong and electroweak penguins in topcolor-assisted technicolor model

Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays from the new strong and electroweak penguin diagrams in the topcolor-assisted technicolor (TC2) model. The top-pion penguins dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes. For tree-dominated decay modes , etc. the new physics corrections are less than 10%. For decays , etc. the new physics enhancements can be rather large (from to ) and are insensitive to the variations of and within reasonable ranges. For the decays and is strongly dependent: varying from to in the range of –. The new physics corrections to the CP-violating asymmetries vary greatly for different B decay channels. For five measured CP asymmetries of the decays, is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting decays are significant in size (), insensitive to the variations of the input parameters and hence lead to a plausible interpretation for the unexpectedly large decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty-seven decay modes are consistent with the available data within one or two standard deviations. Received: 18 August 2000 / Revised version: 22 October 2000 / Published online: 5 February 2001     

Semileptonic Decays of B_s~(**) Mesons into D_(s1) and D_(s2)~* in HQET

In the framework of the heavy quark effective theory,the leading order Isgur-Wise functions relevant to semileptonic decays of the orbitally P-wave excited B s meson states B**s,including the newly found narrow B s1(5830) and B**s2(5840) states,into the(D s1(2536),D*s2(2573)) doublet are calculated from QCD sum rules.With these universal form factors,the decay rates and branching ratios are also estimated.     

Weak Decays of D and Ds Mesons in a Relativistic Quark Model

The transitions of D and D_s, mesons to light vector states are studied in a relativistic constituent quark model based on the Bethe-Salpeter formalism. The form factors are calculated, and the branching fractions for both semileptonic and nonleptonic decays are given. The results show that the form factors for these transitions deviate substantie from the request of heavy quark symmetry. All the branching ratios for D and D_s semileptonic decays are found to be consistent with data, whereas the calculations of nonleptonic D and D_s decays under the factorization assumption do not agree with experiments. This confirms the conjecture that the factorization scheme is much less applicable in D and D_s decays than in B and B_s decays.     

Inclusive charmed-baryon decays and lifetimes

We have quantitatively reanalyzed the inclusive charmed-baryon decays. New ingredients are the Voloshin preasymptotic effects in semileptonic decays and the Cabibbo-subleading contributions to both semileptonic and nonleptonic decays. It has been found that the Cabbibo-subleading Voloshin contribution essentially improves the theoretical semileptonic branching ratio of , in agreement with experiment. The semileptonic branching ratios for and are found to be large, i.e., of the order of 20%. The lifetimes hierarchy is in a good qualitative and even quantitative agreement with experiment except for the lifetime, which is somewhat smaller than the experimental value. Future measurements, especially measurements of the semileptonic branching ratios for , and should be decisive for the check of this approach. Received: 29 April 1997 / Revised version: 25 June 1997 / Published online: 20 February 1998     

Space-like Penguin effects in B_c decays

The space-like penguin contributions to branching ratios and CP asymmetries in charmless decays of to two pseudoscalar mesons are studied using the next-to-leading order low energy effective Hamiltonian and factorization approximation. Both the gluonic penguin and the electroweak penguin diagrams are considered. In addition the annihilation diagram contributions are also taken in account. We find that the space-like penguin effects are significant. Received: 15 December 1997 / Published online: 23 June 1998     

J/Ψ衰变的Roper共振态结构的研究

通过J/Ψ→p, p*, N**衰变,研究了Roper共振态的混杂态结构对衰变角分布和分支比的影响. 计算结果表明,如果Roper共振态为纯混杂态,那么J/Ψ→p*, N**的角分布几乎相等, 而J/Ψ衰变到混杂态的衰变宽度还不到J/Ψ→p 的1%, 给出了Γ(J/Ψ→ N* )/Γ(J/Ψ→p)和Γ(J/Ψ→ N**)/Γ(J/Ψ→ p)随混合参数的变化关系, 并讨论了在J/Ψ衰变中研究Roper混杂态结构的可能性.The structure of Roper resonance is studied as hybrid states through decays J/Ψ→p*, N** by calculating the angular distributions and decay widths. The results show that the angular distribution parameters for decays J/Ψ→p*, N** are almost equal if the Roper is identified as a pure hybrid state, while their decay width are less the 1% of that for the decay J/Ψ→p, and the variance of the ratio Γ(J/Ψ→N*p)/Γ(J/Ψ→p) and Γ(J/Ψ→N**)/ Γ(J/Ψ→p) with the mixing parameter are presented,and also the scheme to identify the Roper structure in J/Ψ decays is discussed.     

Search for exotic baryons with hidden strangeness in diffractive production processes

Experimental results of the SPHINX Collaboration on studying proton diffractive production processes are presented. Evidences for new baryon states with masses 2 GeV were obtained in hyperon-kaon effective mass spectra in several reactions. Unusual properties of these massive states (small enough decay widths, large branching ratios for their decays with strange particles in final states) make them serious candidates for cryptoexotic pentaquark baryons with hidden strangeness . New results for these states are presented here, as well as recent data on large violation of the OZI rule in proton diffractive dissociation.     

Calculation of the yield of Xe<Superscript><Emphasis Type="Italic">i</Emphasis>+</Superscript> photoions upon the decay of <Emphasis Type="Italic">M</Emphasis><Subscript>45</Subscript> vacancies through intermediate states in coincidence with energy-selected Auger electrons

A theoretical model is proposed for calculating the yield of photoions detected in coincidence with energy-selected Auger electrons. This model provides a correct explanation for experimental data on the yield of photoions upon ionization of the M₄₅ shell of xenon atoms. In the framework of the proposed model, the intermediate-coupling approximation is used to calculate both the structure of the terms of the N^?2 two-hole states generated through the M₄₅NN Auger decays and the probabilities of branching due to decays of these states into three-hole states upon the Auger, Coster—Kronig, and super-Coster—Kronig transitions. The probabilities of branching for subsequent branches of the cascade decay are calculated in the configuration-average approximation. The results of these calculations are in good agreement with the experimental data.