新粒子J(3095)衰变过程的分析

本文引入一个统一的机制,试图解释J粒子的辐射衰变和G宇称守恒衰变到普通粒子的过程。这就是J先衰变到φ_n=αφ₁+βφ₈,然后由φ_n衰变到普通粒子。结果如下:1.φ_n≈ω最与实验相符,但给出的Γ(J→ω→ηγ)/Γ(J→ω→πγ)的理论值太小;2.为着定量谐调辐射衰变和二体强子衰变,要求这两类过程的形状因子相差三个数量级。本文从层子模型的图象出发,提出一个计算形状因子的简单模型。计算结果表明,上述形状因子的差别是可以解释的;3.本文还讨论了辐射衰变的另一种机制,并指出存在的问题。     

Supersymmetric signature in quarkonium decays

We calculate the heavy quarkonium decay widths for decays to scalar fermion-scalar antifermion pairs. In the light of the supersymmetric interpretation of the recently observed monojets, these decays could be observable in the forthcoming e⁺−e⁻ colliding beam machines. The scalar lepton-scalar antilepton pairs produced by toponium decays is comparable to those produced by direct photon exchanges. The decays of the scalar pair into an electron-positron (or muon-antimuon) pair (carrying about one-half of the total beam energy) together with the missing photinos will be a clean signature of supersymmetry.     

Induced Higgs couplings to neutral bosons in e+e− collisions

We calculate induced couplings of the type HV_γ in the standard model, where H is a Higgs meson and V is a virtual or real neutral gauge boson (Z⁰ or photon). Numerous applications are given for e⁺e^? collisions and various Higgs meson decays. The calculated rates are in general somewhat too low to make these processed an attractive way to search for the Higgs boson. However, once it has been found, it is argued that these processes should be studied experimentally since the induced couplings probe the structure of the gauge theory in an interesting way. In particular, it may be possible to infer the existence of one or more heavy fermion generations (of mass ?m_Z) by observing their virtual effects in radiative decays into Higgs particles. We also briefly treat the related coupling HV_γ with V a heavy quarkonium vector state.     

Weak radiative decays of hyperons within theSU(6) broken quark-diquark model

In view of persisting discrepancy between experimental and theoretical results, specially in the weak radiative decays of∑ ⁺ andΞ ⁰, we analyse these decays within the framework of the QCD inspired quark-diquark model. On introducing a slightSU(6) breaking we obtainα(∑ ⁺→p+γ)≈?0.9 which is in excellent agreement with experimental value. Other decays are also improved in this scheme.     

Production of P-wave charm and charm-strange mesons in hadronic Z0 decays

Results are presented on the production of excited charm and excited charm-strange mesons in hadronic Z⁰ decays. The results are obtained from approximately 4.3 million hadronic Z⁰ decays, collected on or near the Z⁰ resonance using the OPAL detector at LEP. The D⁰ ₁(2420) and D^*0 ₂ (2460) mesons are reconstructed in the D^*+π^-. final state and their separate production rates in charm fragmentation and in weak decays of b-hadrons are determined. Assuming that the decay widths of these mesons are saturated by the allowed D*π and Dπ final states, the charm hadronization fractions and the inclusive branching ratios of b-hadrons to these neutral P-wave charm mesons are determined to be     

Loop induced flavor changing neutral decays of the top quark in a general two-Higgs-doublet model

Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g., t→H_SM+c, with a branching fraction of 10⁻¹³ at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, the FCNC top quark decays into Higgs bosons, t→(h⁰,H⁰,A⁰)+c, can be the most favored FCNC modes — comparable or even more efficient than the gluon channel t→g+c. In both cases the optimal results are obtained for Type II models. However, only the Higgs channels can have rates reaching the detectable level (10⁻⁵), with a maximum of order 10⁻⁴ which is compatible with the charged Higgs bounds from radiative B-meson decays. We compare with the previous results obtained in the Higgs sector of the MSSM.     

Tensor meson couplings and other results in restricted SU(4)

Tensor meson couplings to two pseudoscalars (TPP) and to a pseudoscalar and a vector (TVP) are studied in the framework of restricted SU(4). This is shown to be consistent with present data and is used to predict both allowed and forbidden decays of new mesons involving the TVP or TPP vertex. In addition, further decays of the ψ, D¹, F¹, and ψ¹ (4.03) are considered.     

Exploring the SUSY Higgs sector ate +e− linear colliders: a synopsis

We discuss the Higgs scenario in the minimal supersymmetric extension of the Standard Model ate ⁺e^? linear colliders operating in the c.m. energy range between 300 and 500 GeV. Besides decays of the Higgs particles into ordinary fermions and cascade decays, we analyze also decays into gaugino/Higgsinos and in particular, neutral Higgs decays into the lightest supersymmetric particles which are invisible ifR-parity is conserved. The cross sections for the various production channels of SUSY Higgs particles ine ⁺e^? collisions are discussed in detail. The lightest Higgs boson cannot escape detection, and in major parts of the MSSM parameter space all five Higgs particles can be observed.     

Isospin violation in mixing and decays of <Emphasis Type="Italic">ρ</Emphasis> and <Emphasis Type="Italic">ω</Emphasis> mesons

The influence of isospin-violating (ρ⁰, ω) mixing is discussed for any pair of decays of ρ⁰, ω into the same final state. It is demonstrated, in analogy to the CP violation in neutral kaon decays, that isospin violation can manifest itself in various forms: direct violation in amplitudes and/or violation due to mixing. In addition to the known decays (ρ⁰, ω) → π⁺π^? and (ρ⁰, ω) → π⁰γ, the pair of decays to e⁺e^? and the whole set of radiative decays with participation of ρ⁰, ω (in initial or final states) are also shown to be useful and promising for studies. Existing data on these decays agree with the universal character of the mixing parameter and indirectly support enhancement of ρ⁰ → π⁰γ in respect to ρ^± → π^±γ. Future precise measurements will allow one to separate different forms of isospin violation and elucidate their mechanisms.     

Pion program for the future rare-decay experiments

The future investigations of rare decays of elementary particles demand the creation of new-generation setups which can perform much greater statistics and precise experimental data. The proposed new setups at CERN, NA62 (NA48/3 (P326SPS)), and at IHEP, OKA, are planned to obtain experimental data at the level of 10⁻¹⁰–10⁻¹² branching ratio. The main goals of both experimental programs are connected with the study of ultrarare kaon decays, but beams of these experiments contain 95% (NA48) and 50% (OKA) of pions. It is natural to use the pion part of these beams for study of rare pion decays. The pion program may be performed simultaneously or consecutively with the main tasks. Such problems as search for tensor interaction, measurements of branching ratio and form factors of some pion decays, effects of polarization, and search for new particles are included in this program. The text was submitted by the authors in English.     

New limits on the double beta decay half-lives of 94Zr, 96Zr, 116Cd and 124Sn

Searches have been made for the double beta decays of ^{94, 96}Zr, ¹¹⁶Cd, and ¹²⁴Sn to excited states in their daughter nuclei. No evidence of any of these decays was found, and lower limits on the half-lives against such decays have been established to be 10¹⁸–10¹⁹ yr. In addition, the single beta decay half-life of ⁹⁶Zr has been established to be ⩾1.4×10¹⁸ yr.     

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.     

Beta processes in a high-temperature field and nuclear multibeta decays

Sources of the temperature dependence of rates of nuclear beta processes in matter of massive stars are systematized. Electron and positron beta decays and electron capture (K capture and the capture of unbound electrons) fromexcited nuclear states (thermal decays) are considered along with the photobeta decays from ground and excited nuclear states. The possible quantum degeneracy of an electron gas in matter and the degree of ionization of an atomic K shell in a high-temperature field are taken into account. For a number of multidecay odd-nuclei, the temperature dependences of the ratios of the total rates of their β ^? decays to the sum of the total rates over all of decay modes for the same nuclei are calculated in the range of nuclear temperature from 2 to 3 × 10⁹ K. It is shown that the deviation of this ratio from the experimental value obtained at “normal” temperature may be quite sizable. This circumstance should be taken into account in models that consider the problem of synthesis of nuclei in matter of massive stars.     

Quark loop model of radiative meson decays

Radiative meson decays are computed from quark loop anomalies, taking into account the SU(3) splitting of the quark masses. Predicted rates for ?→ηγ,K ^*→Kγ, and η→ππγ are brought into satisfactory agreement with experiment. Formulas are given for the radiative decay rates of charmed las are given for the radiative decay rates of charmed mesons, and a mechanism suggested for suppression of the radiative decays of mesons containing a charmed quark.     

Measurement of B d 0 - oscillations

B _d ⁰ meson oscillations are measured in hadronic Z⁰ decays using the charge of a lepton or the mean charge of an event hemisphere to sign the presence of a b or a b? quark when it is produced, and using the charge of a lepton emitted at large pt or of a D*^± to sign the presence of a B or a B? meson when it decays. With 3.2 million hadronic Z⁰ decays registered by DELPHI between 1991 and 1994, the mass difference Δm _d between the two physical B _d ⁰ states is measured in four channels: Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is:      

Role of 8Be → 2 α intermediate nuclei in the fragmentation of 16O relativistic nuclei in nuclear track emulsions

In searches along a track in the chamber irradiated at the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna) with oxygen ions accelerated to a momentum of 4.5 GeV/c per nucleon, 215 events containing two or more doubly charged fragments of the primary nucleus were found. Emission angles in the track-emulsion plane were measured in these events. Their distribution is consistent with that which alpha particles are expected to have in an oxygen nucleus prior to its interaction with a track-emulsion nucleus. Events of the ¹⁶O ?? 2⁸Be ?? 4?? type were discovered for the first time. They are treated as events of the coherent electromagnetic dissociation of an oxygen nucleus. Among all events, about 14% of the ⁸Be ?? 2?? decays proceed through the ground state of spin-parity 0⁺; an approximately the same fraction of such decays proceed through the first excited state of spin-parity 2⁺.     

Model-independent bound on the dark matter lifetime

If dark matter (DM) is unstable, in order to be present today, its lifetime needs to be longer than the age of the Universe, tU?4×¹⁰¹⁷ s$t_U?4\times {10}^{17}\text{s}$. It is usually assumed that if DM decays it would do it with some strength through a radiative mode. In this case, very constraining limits can be obtained from observations of the diffuse gamma ray background. However, although reasonable, this is a model-dependent assumption. Here our only assumption is that DM decays into, at least, one Standard Model (SM) particle. Among these, neutrinos are the least detectable ones. Hence, if we assume that the only SM decay daughters are neutrinos, a limit on their flux from DM decays in the Milky Way sets a conservative, but stringent and model-independent bound on its lifetime.     

The surprising nonleptonic decays

Recent experiments onD-meson decays necessitate a revision of the standard theoretical model for weak decays. In this paper we argue that the presence of gluons in hadrons as required by local color gauge-invariance of Quantum Chromodynamics vitiates, in particular, two assumptions previously made:

1. color suppression factors in amplitudes for weak decays like \(D^0 \to \bar K^0 \pi ^0 \) ,
2. helicity suppression of two-quark interactions in weak decays.

A formula for estimating inclusive rates of mesons decaying via two-quark interactions is derived. Estimates for decay rates and branching ratios of several interesting decays of charmed hadrons are given. In particular, we obtain lifetime estimates forD ⁰,D ⁺, andF ⁺, and we predict the branching ratio for Cabibbo-suppressed decays ofD ⁺ to be of order 0.3 rather than of order tan²Θ _c as expected within the conventional model for weak decays.B-meson decays, which would provide an additional test of our scheme, are briefly discussed. Furthermore we point out that our approach sheds new light on the old problem of strongly enhanced |ΔI|=1/2 amplitudes in nonleptonic decays of strange particles.     

Tests of various models for the weak decays of heavy flavour states

It is discussed how two models which were proposed to explain the lifetime difference betweenD ⁰ andD ⁺ mesons can be subjected to further tests. These two models are the “SU (4) 20-plet dominance” model and the “gluon bremstrahlung” model forW exchange. The tests can be performed by studying inclusive decays—e.g.,F ⁺ lifetime or semi-leptonic branching ratio—or special exclusive modes in the non-leptonic and semileptonic decays. It is suggested thatF ⁺ semi-leptonic decays can lead to glueball production. The decays of bottom mesons are discussed in this context, too.