arXiv subjects
Publications and source records attributed to I. A. Koop.
The cross section for the process $e^+e^- \to ωη$ is measured in the center-of-mass energy range 1.34--2.00 GeV. The analysis is based on data collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured $e^+e^- \to ωη$ cross section is the most accurate to date. A significant discrepancy is observed between our data and previous BABAR measurement.
The process $e^+e^- \to π^0γ$ has been studied in the experiment with the SND detector at the VEPP-2M $e^+e^-$ collider. The $e^+e^- \to π^0γ$ cross section has been measured in the center-of-mass energy range from 0.60 to 1.38 GeV. The cross section is well described by the vector meson dominance model. From the fit to the cross section data we have determined the branching fractions $B(ρ\toπ^0γ)=(4.20\pm0.52)\times10^{-4}$, $B(ω\toπ^0γ)=(8.88\pm0.18)\%$, $B(ϕ\toπ^0γ)=(1.367\pm0.072)\times10^{-3}$, and the relative phase between the $ρ$ and $ω$ amplitudes $φ_ρ=(-12.7\pm4.5)^\circ$. Our data on the process $e^+e^- \to π^0γ$ are the most accurate to date.
Using a data sample of 6.8 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider we select about 2700 events of the $e^+e^- \to p\bar{p}$ process and measure its cross section at 12 energy ponts with about 6\% systematic uncertainty. From the angular distribution of produced nucleons we obtain the ratio $|G_{E}/G_{M}| = 1.49 \pm 0.23 \pm 0.30$.
The process $e^+e^- \to K^+K^-π^+π^-$ has been studied in the center-of-mass energy range from 1500 to 2000\,MeV using a data sample of 23 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. Using about 24000 selected events, the $e^+e^- \to K^+K^-π^+π^-$ cross section has been measured with a systematic uncertainty decreasing from 11.7\% at 1500-1600\,MeV to 6.1\% above 1800\,MeV. A preliminary study of $K^+K^-π^+π^-$ production dynamics has been performed.
A sensitivity of the VEPP-2000 $e^+e^-$ collider in a search for the rare decay $η\rightarrow e^+ e^-$ has been studied. The inverse reaction $e^+ e^- \rightarrow η$ is proposed for this search. We have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction $e^+ e^- \rightarrow η$ in the decay mode $η\toπ^0π^0π^0$. In the absence of background, a sensitivity to ${\cal B}(η\rightarrow e^+ e^-)$ of $10^{-6}$ can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on ${\cal B}(η\rightarrow e^+ e^-)$ by a factor of 2.3.
A search for the process $e^+e^- \to η^\prime$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The data were accumulated at the center-of-mass energy of $957.78\pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $η^\prime$ meson five decay chains have been used: $η^{\prime}\toηπ^+π^-$ followed by the $η$ decays to $γγ$ and $3π^0 $, and $η^{\prime} \to ηπ^0π^0$ followed by the $η$ decays to $π^+π^-π^0$, $γγ$, and $3π^0$. As a result, the upper limit has been set on the $η^\prime$ electronic width: $Γ_{η^{\prime}\to e^+e^-} < 0.0020$ eV at the 90\% confidence level.
In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider the cross section for the process $e^+e^-\toηπ^+π^-$ has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the $e^+e^-\toηπ^+π^-$ cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions $B(ρ(1450)\toηπ^+π^-)B(ρ(1450)\to e^+e^-)$ has been extracted and compared with the same products for $ρ(1450)\toωπ^0$ and $ρ(1450)\toπ^+π^-$ decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.
A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of $10^{-29}e\cdot$cm by using polarized "magic" momentum $0.7$~GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the Standard Model at the scale of 3000~TeV.
A search for the process $\epem\to η^\prime(958)$ in the $\pipiη\to\pipiγγ$ final state has been performed with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. Using an integrated luminosity of 2.69 pb$^{-1}$ collected at the center-of-mass energy \Ecm = 957.68 MeV we set an upper limit for the product of electronic width and branching fractions $Γ_{η^\prime(958)\to\epem}\cdot\BR_{η^\prime(958)\to\pipiη}\cdot\BR_{η\toγγ}<0.00041$ eV at 90\% C.L.
The process $e^+e^-\to n\bar{n}$ has been studied at the VEPP-2000 $e^+e^-$ collider with the SND detector in the energy range from threshold up to 2 GeV. As a result of the experiment, the $e^+e^-\to n\bar{n}$ cross section and effective neutron form factor have been measured.
The $e^+e^-\toηγ$ cross section has been measured in the center-of-mass energy range 1.07--2.00 GeV using the decay mode $η\to 3π^0$, $π^0\to γγ$. The analysis is based on 36 pb$^{-1}$ of integrated luminosity collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured cross section of about 35 pb at 1.5 GeV is explained by decays of the $ρ(1450)$ and $ϕ(1680)$ resonances.
The beam energy measurement system for the VEPP-2000 electron-positron collider is described. The method of Compton backscattering of $CO$ laser photons on the electron beam is used. The relative systematic uncertainty of the beam energy determination is estimated as 6\cdot10^{-5}. It was obtained through comparison of the results of the beam energy measurements using the Compton backscattering and resonance depolarization methods.
The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.
The cross section of the process $e^+e^- \to 3(π^+π^-)$ has been measured using 22 pb$^{-1}$ of integrated luminosity collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider in the c.m. energy range 1.5 -- 2.0 GeV. The measured cross section exhibits a sharp drop near the $p\bar p$ threshold. A first study of dynamics of six-pion production has been performed.
The $ϕ$(1020) meson leptonic width has been determined from the combined analysis of 4 major decay modes of the resonance ($ϕ\to K^+ K^-,K^0_LK^0_S,π^+π^-π^0,ηγ$) studied with the CMD-2 detector at the VEPP-2M $e^+e^-$ collider. The following value has been obtained: $Γ(ϕ\to e^+e^-) = 1.235\pm 0.006\pm 0.022$ keV. The $ϕ(1020)$ meson parameters in four main decay channels have been also recalculated: $B(ϕ\to K^+K^-) = 0.493\pm 0.003\pm 0.007$, $B(ϕ\to K_LK_S) = 0.336\pm 0.002\pm 0.006$, $B(ϕ\toπ^+π^-π^0) = 0.155\pm 0.002\pm 0.005$, $B(ϕ\toηγ) = 0.0138\pm 0.0002\pm 0.0002$.
The search for lepton-flavor-violation process e^+e^-\to eμin the energy region \sqrt{s}=984 - 1060 MeV with SND detector at VEPP-2M e^+e^- collider is reported. The model independent 90% CL upper limits on the e^+e^-\to eμcross section, σ_{eμ} < 11 pb, as well as on the corresponding ϕ\to eμbranching fraction, B(ϕ\to eμ) < 2 \times 10^{-6}, for the final particles polar angles 55^\circ<θ<125^\circ, were obtained.
The cross section of the process e+e-\toμ+μ- was measured in the SND experiment at the VEPP-2M e+e- collider in the energy region \sqrt{s}=980, 1040 -- 1380 MeV. The event numbers of the process e+e-\toμ+μ- were normalized to the integrated luminosity measured using e+e-\to e+e- and e+e-\toγγprocesses. The ratio of the measured cross section to the theoretically predicted value is 1.006\pm 0.007 \pm 0.016 and 1.005 \pm 0.007 \pm 0.018 in the first and second case respectively. Using results of the measurements, the electromagnetic running coupling constant αin the energy region \sqrt{s}=1040 -- 1380 MeV was obtained <1/α> = 134.1\pm 0.5 \pm 1.2 and this is in agreement with theoretical expectation.
The process e+ e- -> phi -> K+ K- has been studied with the CMD-2 detector using about 542 000 events detected in the center-of-mass energy range from 1.01 to 1.034 GeV. The systematic error of the cross section is estimated to be 2.2%. The phi(1020) meson parameters in the phi -> K+K- decay channel have been measured: sigma_0(phi-> K+K-) = 2016 +- 8 +- 44 nb, m(phi) = 1019.441 +- 0.008 +- 0.080 MeV/c2, Gamma(phi) = 4.24 +- 0.02 +- 0.03 MeV, B(e+e-)B(K+K-) = (14.27 +- 0.05 +- 0.31)*10(-5).