The final-focus solenoids of the VEPP‑2000 round-beam e+e− collider are able to cause stopbands in the betatron tune plane. The available tune space in the most important region near the parametric resonances (above the integer tunes) is limited by this specific stopband domain. The combined effect of the decompensated solenoids and the parametric resonances at the integers is theoretically studied. The results are complemented with numerical investigations and simulation using the RING program. The stability domain boundaries in the betatron tune plane have been experimentally determined, and their position is in good agreement with the theoretical expectations.

A single-turn (and single-bunch) injection often operates with an injection portion of high intensity, comparable with that of the circulating bunch. Collective effects due to transverse impedance provide interaction between groups of par- ticles. This interaction may set serious limitations on the injection efficiency.We analyze the conditions of coherency of the betatron oscillations following the injection, while the beam is subject to decoherence resulting from the machine lattice nonlinearities. The theoretical results are supported by numerical track- ing. The conclusions are compared with experimental data on dipole oscillations histories following the VEPP-2000 injection.

The cross section of the process e+e- -> x-+x-- has been measured in the center of mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on a full dataset collected below 1 GeV during three data taking seasons, corresponding to an integrated luminosity of about 62 pb-1. In the dominant p-resonance region, a systematic uncertainty of 0.7% has been reached. At energies around 0-resonance the x-+x-- production cross section was measured for the first time with high beam energy resolution. The forward-backward charge asymmetry in the x-+x-- production has also been measured. It shows a strong deviation from the theoretical prediction based on the conventional scalar quantum electrodynamics framework, and it is in good agreement with the generalized vector-meson-dominance and dispersive-based predictions. The impact of the presented results on the evaluation of the hadronic contribution to the anomalous magnetic moment of muon is discussed.

The e^+e^-→ηγ cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel η→ 3π^0 , π^0→γγ . The data set with an integrated luminosity of 242 pb ^-1 accumulated in the experiment with the SND detector at the VEPP-2000 e^+e^- collider is analyzed.

The process e^+e^-→π^+π^-π^0 was studied in the energy range between 1.075 and 1.975 GeV on the basis of data characterized by an integrated luminosity of about 70 pb ^-1 that were accumulated in an experiment with the Spherical Neutral Detector (SND) at the VEPP-2000 e^+e^- collider. The respective Dalitz distributions were analyzed within a model that includes ρ(770)π , ρ(1450)π , and ωπ^0 intermediate states. As a result, the energy dependences of the total cross section for the process e^+e^-→π^+π^-π^0 and the cross sections for the ρ(770)π and ρ(1450)π intermediate states were measured along with the phase shift of the ρ(770)π amplitude with respect to the ρ(1450)π and ωπ^0 amplitudes. For the first time, a simultaneous approximation of the cross sections for the processes e^+e^-→ρ(770)π and ρ(1450)π and the relative phase of the respective final states was performed on the basis of the vector-meson dominance model. The contributions of the ω , ϕ , ω(1420) , and ω(1650) resonances were taken into account. The approximation showed that the decay ω(1650)→π^+π^-π^0 proceeds predominantly through the ρ(1450)π intermediate state, while the decay ω(1420)→π^+π^-π^0 receives a dominant contribution from the ρ(770)π mechanism. The results of this study refined the results of earlier measurements with the SND setup.

The cross section of the process $e^+e^-\to\pi^+\pi^-$ has been measured in the center-of-mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on an integrated luminosity of about 88 pb$^{-1}$, of which 62 pb$^{-1}$ represent a complete dataset collected by CMD-3 at center-of-mass energies below 1 GeV. In the dominant region near the $\rho$ resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed.

CCD cameras are easy to use and are quite widespread in the optical diagnostics of beams in particle accelerators. The exposure time of these cameras is milliseconds, so they are usually used in a cumulative mode to monitor the circulating beams. The images from the cameras contain information about the transverse distribution of particles in the beam and the position of the center of mass of the beam. In this paper, using the example of CCD cameras installed on the electron-positron collider VEPP-2000, the possibility of their use in the mode of a single beam flight through the observation site is investigated. The intensity of the luminous flux of the optical part of the synchrotron radiation spectrum of the beam was estimated and an image of the transverse distribution of particles in the beam in a single-span mode was experimentally obtained, which confirms the potential for expanding the scope of this diagnostic system. A trial signal processing was done as a demonstration of the determination of the beam parameters by the method under study.

The process e+e−→ωπ0→π+π−π0π0 is studied in the center-of-mass energy region 1.05–2.00 GeV using data with an integral luminosity of about 35 pb−1 collected with the SND detector at the VEPP-2000 e+e− collider. In the energy range under study, the value of the measured Born cross section varies from 0.7 to 18 nb. The statistical uncertainty of the cross section is 2%–23%, while the systematic uncertainty is in the range of 3.0%–14.2%. The results are consistent with previous measurements but have better accuracy.4 MoreReceived 6 September 2023Accepted 1 November 2023DOI:https://doi.org/10.1103/PhysRevD.108.092012Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHadron productionLepton-lepton interactionsPhysical SystemsLight mesonsPropertiesForm factorsParticles & Fields

The e+e− → ηγ cross section is measured in the center-of-mass energy range from 1.07 to 2.00 GeV in the decay channel η → 3π0, π0 → γγ. The data set with an integrated luminosity of 242 pb−1accumulated in the experiment with the SND detector at the VEPP-2000 e+e− collider is analyzed.

The VEPP-2000 is an electron–positron collider with round beams built and operating at the Budker Institute of Nuclear Physics (BINP). The collider luminosity was increased twofold last year. The integrated luminosity accumulated over the last year has exceeded 0.3 fb –1 , which almost doubled the total data collected since the collider operation began. The short description of the VEPP-2000 complex, current status, and the results are presented in this work.

The process $e^+e^- \to \omega\pi^0 \to \pi^+\pi^-\pi^0\pi^0$ is studied in the center-of-mass energy region $1.05-2.00$ GeV using data with an integral luminosity of about 35 pb$^{-1}$ collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. In the energy range under study, the value of the measured Born cross section varies from 0.7 to 18 nb. The statistical uncertainty of the cross section is $2-23$%, while the systematic uncertainty is in the range of $3.0-14.2$%. The results are consistent with previous measurements but have better accuracy.

AbstractThe process $$e^+e^-\rightarrow n{\bar{n}}$$ e + e - → n n ¯ is studied in the experiment at the VEPP-2000 $$e^+e^-$$ e + e - collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select $$n{\bar{n}}$$ n n ¯ events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.

The process e^+e^-→ nn̅ is studied in the experiment at the VEPP-2000 e^+e^- collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select nn̅ events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.

VEPP-2000 electron-positron collider operating in the beam energy range of 150-1000 MeV is the only machine originally designed for and successfully exploiting Round Beams Concept. After injection chain upgrade including link to the new BINP injection complex VEPP-2000 proceeded with data taking since 2017 with luminosity limited only by beam-beam effects. At the low energies (300-600 MeV/beam) the novel technique of effective emittance controlled increase by weak coherent beam shaking allowed to suppress the limiting flip-flop effect and resulted in additional luminosity gain factor of 4. The averaged delivered luminosity at the omega-meson production energy (2×391 MeV) achieved L =2×1031 cm2s1/IP. At the top energies above nucleonantinucleon production threshold the stable operation with luminosity of L = 5×1031 cm2s1/IP resulted in high average data taking rate of 2 pb1/day in 2020.

A bstract The cross section of the process e + e − → π + π − has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 e + e − collider VEPP-2000 in the energy region 525 < $$ \sqrt{s} $$ s < 883 MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb − 1 . The systematic uncertainty of the cross section determination is 0.8% at $$ \sqrt{s} $$ s > 0 . 600 GeV. The ρ meson parameters are obtained as m ρ = 775 . 3 ± 0 . 5 ± 0 . 6 MeV, Γ ρ = 145 . 6 ± 0 . 6 ± 0 . 8 MeV, B ρ → e + e− × B ρ → π + π− = (4 . 89 ± 0 . 02 ± 0 . 04) × 10 − 5 , and the parameters of the e + e − → ω → π + π − process, suppressed by G -parity, as B ω → e + e− × B ω → π + π− = (1 . 32 ± 0 . 06 ± 0 . 02) × 10 − 6 and and ϕ ρω = 110 . 7 ± 1 . 5 ± 1 . 0 degrees.

In the vicinity of the linear coupling resonance where the working point of the collider is positioned, we study the effect of nonlinear coupling resonances on the single-particle phase space, beam sizes and the waveform of coherent beam motion. The latter is interesting for diagnostics of the nonlinear dynamics.