Study of conversion decays φ→ηe+e− and η→γe+e− in the experiment with SND detector at VEPP-2M collider

The conversion decays φ→ηe⁺e⁻ and η→γe⁺e⁻ were studied by the SND detector using φ-meson production in e⁺e⁻-annihilation at VEPP-2M collider. The branching ratios of these decays were measured: Br(φ→ηe⁺e⁻)=(1.19±0.19±0.07)×10⁻⁴ and Br(η→γe⁺e⁻)=(5.15±0.62±0.39)×10⁻³. The e⁺e⁻-pair mass spectra and transition form factors were also studied.     

Searching for the process e+e- → K+K-π0 in experiments with the spherical neutral detector at VEPP-2M

We have searched for the process e⁺e^- → K⁺K^-π⁰ at energies up to 1.38 GeVin an experiment with the spherical neutral detector at the VEPP-2M e⁺e^- collider. The upper limits of the cross sections for the processes σ(e⁺e →; φπ: → K⁺K^-π⁰) < 0.023 nb and σ(e⁺e^- → KK*(892) → K⁺K^-π⁰) < 0.059 nb have been established at a 95% confidence level.     

The process e + e − → bb̅W + W − at the next linear collider in the Minimal Supersymmetric Standard Model

The complete matrix element for e ⁺ e^? → bb?W⁺ W^? is computed at tree-level within the Minimal Supersymmetric Standard Model. Rates of interest to phenomenological analyses at the Next Linear Collider are given. In particular, we study:

• ? tt? production and decay tt? →(bW ⁺)(b?W ^?)
• ? ZH production followed by Z → bb? and H → W ⁺ W^?
• ? AH production followed by A→ bb? and H → W ⁺ W^?
• ? hW ⁺ W^? production followed by h→ bb?.

Top and Higgs finite width effects are included, as well as all those of the irreducible backgrounds.     

A new upper limit for the branching ratio of the decay K0S → e+e−

A new value of the upper limit for the branching ratio of the decay of K⁰_S into e⁺e⁻ has been experimentally obtained using a lead glass detector. The value is BR (K⁰_S → e⁺e⁻) < 1.1 × 10⁻⁴ (90% CL).     

Measurement of the e + e − → ηπ+π− cross section in the \sqrt s = 1.04–1.38-GeV energy range with a spherical neutral detector at the VEPP-2M collider

The e ⁺ e ^? → ηπ⁺π^? cross section in the η → 2γ channel has been measured in the $ \sqrt s $ = 1.04- to 1.38-GeV energy range. The data with a total integrated luminosity of 9.05 pb^?1 were collected on a spherical neutral detector at the VEPP-2M collider. The results are consistent with the BaBar and CMD2 data and have a higher statistical accuracy.     

Searches for electroweak γ-Z-Z’ interference at the LEP2 e + e − collider

Indirect effects of the Z’ boson in the process e ⁺ e ^? → μ⁺μ^? as implemented at the LEP2 electron-positron collider are investigated in terms of new integrated observables σ^±. It is demonstrated that these observables furnish more definitive information about Z’-boson effects than the canonical observables σ_± and A _FB. It is established that the deviations Δσ^± induced by Z’ bosons show a specific energy dependence, which is determined primarily by the parameters of the Standard Model. This permits making unambiguous model-independent predictions. In particular, two points, $\sqrt {s_ + } \approx 78GeV$ and $\sqrt {s_ - } \approx 113GeV$ , are determined at which, respectively, σ₊ and σ_? vanish both in the Standard Model and in presence of the extra Z’ boson. These energy values can be of use in searches for phenomenological manifestations of alternative sources of new physics that are different from Z’.     

Search for the radiative decay η→π0γγ in the SND experiment at VEPP-2M

The η→π⁰γγ decay was investigated by the SND detector at VEPP-2M e⁺e⁻ collider in the reaction e⁺e⁻→φ→ηγ. Here we present the results and some details of this study. We report an upper limit (90% c.l.) Br(η→π⁰γγ)<8.4×10⁻⁴ as our final result. Our upper limit does not contradict the earlier measurement by GAMS spectrometer. To facilitate future studies a rather detailed review of the problem is also given.     

The process e + e − → ωπ0 near the Φ resonance

The reaction e ⁺ e ^?→ωπ⁰ near a Φ resonance was studied with a spherical neutral detector at VEPP-2M e ⁺ e ^? collider. Both main modes of decay of a ω meson were investigated: ω→π⁺π^?π⁰ and ω→π ⁰γ. The probability of decay Φ→ωπ⁰ was obtained from the magnitude of the interference wave in the cross section for the reaction e ⁺ e ^?→ωπ⁰→ π⁺π^?π⁰π⁰: B(Φ→ωπ⁰) = (5.5 _?1.4 ^+1.6 ±0.3) ×10^?5. The ratio of the partial widths of the ω meson was obtained from the ratio of the cross sections for the two modes: Γ(ω→π⁰γ )/Γ(ω→π⁺π^?π⁰) = 0.0994 ± 0.0036 ± 0.0038.     

Effect of weak neutral currents in the process e− + p → e− + γ + X

Polarization effects in the inclusive process e^– + p e^– + + X due to the neutral current are studied in the framework of the Weinberg-Salam model. Expressions for the asymmetry parameters and the degree of circular polarization of the photons are obtained in the quark-parton picture. It is shown that measurement of such quantities gives additional information about the quark structure of the hadronic weak neutral current.Paper presented at the scientific session of the nuclear physics branch, USSR Academy of Sciences and the Moscow State University on Electromagnetic and Weak Interactions (Moscow, January 16–20, 1979).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 96–99, January, 1981.     

Limits on light higgs bosons from the decays K±→π±l−l+

Current experimental limits on K^±→π^±e⁻e⁺ rule out a neutral scalar particle with the couplings of the standard Higgs boson and mass in the range 50 MeV to 211 MeV. Planned experimental improvements could lead to a bound m_H ⩾ m_K−m_π.     

Search for the decay τ− → vτηπ−

We have searched for the decay τ⁻ → v_τηπ⁻ using data accumulated by the ARGUS detector at the e⁺e⁻ storage ring DORIS II at DESY. No η signal was found in the π⁺π⁻π⁰ subsystems of the decay τ⁻ →v_τπ⁻π⁻π⁺ π⁰. We obtain an upper limit for the branching ratio of the decay τ⁻ → v_τηπ⁻ of 1.3% at the 95% confidence level.     

Search for the ϕ → π+π−γγ and ϕ → π+π−η decays with the CMD-2 detector

The ? → π⁺π^?γγ and ? → π⁺π^?η decays are sought in the experimental data obtained with the CMD-2 detector in the region of the ?-meson resonance. Upper limits ?(? → ππγγ)< 1.2 × 10^?4 and ?(? → ππη) < 6.1 × 10^?5 (both at a C.L. of 90%) are determined for the branching ratios of these decays.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Search for rare radiative decays ofΦ-meson at VEPP-2M

Results of the search for rare radiative decay modes of the ?-meson performed with the Neutral Detector at the VEPP-2M collider are presented. For the first time upper limits for the branching ratios of the following decay modes have been placed at 90% confidence level: $$\begin{gathered} B(\phi \to \eta '\gamma )< 4 \cdot 10^{ - 4} , \hfill \\ B(\phi \to \pi ^0 \pi ^0 \gamma )< 10^{ - 3} , \hfill \\ B(\phi \to f_0 (975)\gamma )< 2 \cdot 10^{ - 3} , \hfill \\ B(\phi \to H\gamma )< 3 \cdot 10^{ - 4} , \hfill \\ \end{gathered} $$ whereH is a scalar (Higgs) boson with a mass 600 MeV<m _H <1000 MeV, the real measurement isB(φ→H γ)·B(H→2π⁰)<0.8·10^-4, the quoted result is model dependent, as explained in the text, $$\begin{gathered} B(\phi \to a\gamma ) \cdot B(a \to e^ + e^ - )< 5 \cdot 10^{ - 5} , \hfill \\ B(\phi \to a\gamma ) \cdot B(a \to \gamma \gamma )< 2 \cdot 10^{ - 3} , \hfill \\ \end{gathered} $$ wherea is a particle with a low mass and a short lifetime, $$B(\phi \to a\gamma )< 0.7 \cdot 10^{ - 5} ,$$ wherea is a particle with a low mass not observed in the detector.     

Search for CP violation in τ±→K(S)0π±ντ decays at Belle

We report on a search for CP violation in τ(±)→K(S)(0)π(±)ν(τ) decays using a data sample of 699 fb(-1) collected by the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the K(S)(0)π(±) system and found to be compatible with zero with a precision of O(10(-3)) in each mass bin. Limits for the CP violation parameter Im(η(S)) are given at the 90% confidence level. These limits are |Im(η(S))| < 0.026 or better, depending on the parametrization used to describe the hadronic form factors, and improve upon previous limits by 1 order of magnitude.     

Limits on a lepton-number violating process from e+e− collisions

If a new hypothetical particle induces a lepton-number violating process, it could also affect the reactions e⁺e⁻→μ⁺μ⁻ and e⁺e⁻→τ⁺τ⁻ through the t-channel exchange of the particle. A fit of the cross sections and forward-backward asymmetries measured by experiments at PEP and PETRA yields the 90% confidence level limits on the coupling of the partile: G_eμ < 0.119G_F and G_eτ < 0.085G_F, where G_F is the Fermi coupling constant. These limits exclude certain regions of couplings allowed by other lepton-number violating searches.