arXiv subjects
Publications and source records attributed to Yu. M. Shatunov.
The program of upgrade of the Spherical Neutral Detector for future experiments at a new VEPP-2000 $e^+e^-$ collider is presented. Modernization includes upgrades of electromagnetic calorimeter, tracking system, detector electronics, data acquisition system, and offline software. It is also planned to equip the detector with two new subsystems: particle identification system based on aerogel Cherenkov counters and external electron tagging system for $γγ$ physics.
The cross sections of the processes $e^+e^- \to K^+K^-$, $e^+e^- \to K_SK_L$ and $e^+e^- \to π^+π^-π^0$ were measured in the SND experiment at the VEPP-2M collider in the energy region near the $ϕ(1020)$ meson. These measurements were based on about $10^6$ $K^+K^-$, $0.5 \times 10^6$ $K_SK_L$ and $0.4 \times 10^6$ $π^+π^-π^0$ selected events. Themeasured cross sections have been analyzed in the framework of the vector meson dominance model and the main parameters of the $ϕ$-resonance were obtained, such as its mass, width, the production cross section and branching ratios of the main decay modes. The measured value of the $ϕ$ meson total width, $Γ_ϕ = 4.21 \pm 0.04$ is lower than the present world average of $4.458 \pm 0.032$ MeV. Contributions in addition to the conventional vector meson dominance model were found in the $e^+e^- \to π^+π^-π^0$ reaction cross section.
The process e+e-->mu+mu- has been studied by SND detector at VEPP-2M e+e- collider in the phi(1020)-resonance energy region. The measured effective phi meson leptonic branching ratio: B(phi->l+l-)=sqrt{B(phi->e+e-)*B(phi->mu+mu-)}=(2.89+-0.10+-0.06)*10^{-4} agrees well with the PDG value B(phi->e+e-)=(2.91+-0.07)*10^{-4} confirming mu-e universality. Without additional assumption of mu-e universality the branching ratio B(phi->mu+mu-)=(2.87+-0.20+-0.14)*10^{-4} was obtained.
The $η\to π^0 γγ$ decay was investigated by the SND detector at VEPP-2M $e^+e^-$ collider in the reaction $e^+e^-\toϕ\to ηγ$. Here we present the results and some details of this study. We report an upper limit (90% c.l.) $Br(η\to π^0 γγ)<8.4\times 10^{-4}$ 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 current status of experiments with SND detector at VEPP-2M $e^+e^-$ collider in the energy range $2E_0=0.4-1.4$ GeV is given. The new results of analysis of $ϕ$ decay into $π^0π^0γ$, $ηπ^0γ$ are based on the full SND statistics corresponding 20 million of $ϕ$ decay. New measurement of $ω\toπ^0π^0γ$ decay and a first observation of $ρ\toπ^0π^0γ$ are presented. The accuracy of many other rare decays of light vector mesons was improved. In the energy range $2E_0=1.0\div1.4$ GeV the cross sections of the processes $e^+e^-\toωπ^0$ and $e^+e^-\toπ^+π^-π^0$ were measured. The results of the fitting of data are discussed.
A search for direct production of C-even resonances a2(1320) and f2(1270) in e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The upper limits of electronic widths of these mesons were obtained at 90% confidence level: Gamma(a2(1320) \to e+e-) < 0.56 eV, Gamma(f2(1270) \to e+e-) < 0.11 eV.
The cross section of the $e^+e^-\toωπ^0\toπ^0π^0γ$ reaction was measured by the SND detector at VEPP-2M $e^+e^-$ collider in the energy range from threshold up to 1.4 GeV. Results of the cross section fitting by the sum of $ρ$, $ρ^{\prime}$ and $ρ^{\prime\prime}$ contributions are presented.
In the SND experiment at VEPP-2M $e^+e^-$ collider the $ϕ(1020)\toπ^0π^0γ$ decay was studied and its branching ratio was measured: $B(ϕ\toπ^0π^0γ)=(1.221\pm 0.098\pm0.061)\cdot10^{-4}$. It was shown, that $f_0(980)γ$ intermediate state dominates in this decay and the $f_0(980)$-meson parameters were obtained.
Rare radiative decay $ϕ\toηπ^0γ$ was studied with SND detector at {VEPP-2M} electron-positron collider and its branching ratio was measured: $B(ϕ\toηπ^0γ)=(0.88\pm0.14\pm0.09)\cdot 10^{-4}$. Significant contribution of the $a_0(980)γ$ intermediate state was observed in the decay. The result is based on total integrated luminosity corresponding to $2\cdot10^7$ produced $ϕ$ mesons.
The process e+e- ->pi+pi- has been studied with the SND detector at VEPP-2M e+e- collider in the vicinity of phi(1020) resonance. From the analysis of the energy dependence of measured cross section the branching ratio B(phi->pi+pi-)=(7.1+-1.1+-0.9)*10^{-5} and the phase psi_pi=-(34+-4+-3)degrees of interference with the non-resonant pi+pi- production amplitude were obtained.
The new data on $ρ,ω,ϕ$ radiative decays into $π^0γ,ηγ,η'γ$ from SND experiment at VEPP-2M $e^+e^-$ collider are presented.
The processes $e^+e^-\toμ^+μ^-$ and $e^+e^-\toπ^+π^-$ have been studied with SND detector at VEPP-2M $e^+e^-$ collider in the vicinity of $ϕ(1020)$ resonance. The branching ratios $B(ϕ\toμ^+μ^-)=(3.30\pm 0.45\pm 0.32)\times 10^{-4}$ and $B(ϕ\toπ^+π^-)=(0.71\pm 0.11\pm 0.09)\times 10^{-4}$ were obtained.
The current status of experiments with SND detector at VEPP-2M e^+e^- collider in the energy range 2E_0=400-1400 MeV and recent results of data analysis for $ϕ$, $ω$ and $ρ$ decays and e^+e^- annihilation into hadrons are presented.
In the experiment with the SND detector at VEPP-2M e^+e^- collider the process $e^+e^-\toπ^+π^-π^0$ was studied in the energy range 2E_0 from 1.04 to 1.38 GeV. A broad peak was observed with the visible mass $M_{vis}=1220\pm 20$ MeV and cross section in the maximum $σ_0\simeq 4$ nb. The peak can be interpreted as a $ω$-like resonance $ω(1200)$.
Results of the SND experiment at the VEPP-2M e+ e- collider on the QED processes e+ e- --> e+ e- gamma and e+ e- --> e+ e- gamma gamma with production at large angles are presented. Energy and angular distributions of the final particles were studied. No deviations from QED with an accuracy of 3.8% for the first process and 10.3% for the second were found.
The search for CP-violating K_S\to3π^0 decay was performed with SND detector at VEPP-2M e^+e^- collider. The total amount of data corresponding to 7 million produced K_S mesons was analyzed. No candidate events were found, giving an upper limit of the decay branching ratio: Br(K_S\to3π^0) < 1.4\cdot10^{-5} at 90% confidence level.
The process e^+e^- ->mu^+mu^- has been studied with SND detector at VEPP-2M e^+e^- collider in the vicinity of phi(1020) resonance. The product of branching ratios of phi meson into leptons \sqrt{B(phi->mu^+mu^-) B(phi-> e^+e^-)}=(3.14+-0.22+-0.14)x10^{-4} was measured from the interference in the cross section of the process e^+e^- ->mu^+mu^-. The branching ratio B(phi->mu^+mu^-)=(3.30+-0.45+-0.32)x10^{-4} was obtained.
The reaction e^+e^- ---> OMEGA+PI0 ---> PI+PI- 2PI0 has been studied with SND detector at VEPP-2M e^+e^- collider in the vicinity of the PHI(1020) meson resonance. The observed interference pattern in the energy dependence of the cross section is consistent with existence of the decay PHI ---> OMEGA+PI0 with a branching ratio of B(PHI ---> OMEGA+PI0)=(4.8+1.9-1.7+-0.8)x10^{-5}. The real and imaginary parts of the decay amplitude were measured. The PHI ---> OMEGA+PI0 decay was observed for the first time.