V.Sh. Banzarov

Update: A reanalysis of hadronic cross section measurements at CMD-2

The updated results of the precise measurements of the processes e+e-->rho->pi+pi-, e+e-->omega->pi+pi-pi0 and e+e-->phi->KLKS performed by the CMD-2 collaboration are presented. The update appeared necessary due an overestimate of the integrated luminosity in previous analyses.

Measurement of e+e- → π+π- cross-section with CMD-2 around ρ-meson

The cross section of the process e+e- ->pi+pi- has been measured using about 114000 events collected by the CMD-2 detector at the VEPP-2M e+e- collider in the center-of-mass energy range from 0.61 to 0.96 GeV. Results of the pion form factor determination with a 0.6% systematic uncertainty are presented. Implications for the hadronic contribution to the muon anomalous magnetic moment are discussed.

High-statistics measurement of the pion form factor in the ρ-meson energy range with the CMD-2 detector

We present a measurement of the pion form factor based on e+e- annihilation data from the CMD-2 detector in the energy range 0.6<sqrt(s)<1.0 GeV with a systematic uncertainty of 0.8%. A data sample is five times larger than that used in our previous measurement.

Measurement of the e + e - → π+π- cross section with the CMD-2 detector in the 370-520-MeV energy range

The cross section of the process e+e- ->pi+pi- has been measured at the CMD-2 detector in the 370-520 MeV center-of-mass (c.m.) energy range. A systematic uncertainty of the measurement is 0.7 %. Using all CMD-2 data on the pion form factor, the pion electromagnetic radius was calculated. The cross section of muon pair production was also determined.The results of the experiment on the measurement of the e+e− → π+π− cross section in a cm energy range of 370–520 MeV are presented. The systematic measurement error is equal to 0.7%. In the vector dominance model, the pion electromagnetic radius is calculated using all the CMD-2 data on the pion form factor. The cross section for the production of a muon pair is measured in the energy range of the experiment.

a1(1260)π dominance in the process e+e−→4π at energies 1.05–1.38 GeV

First results of the study of the process e+e- \to 4\pi by the CMD-2 collaboration at VEPP-2M are presented for the energy range 1.05--1.38 GeV. Using an integrated luminosity of 5.8 pb^{-1}, energy dependence of the processes e+e- \to \pi^+\pi^- 2\pi^0 and e+e- \to 2\pi^+ 2\pi^- has been measured. Analysis of the differential distributions demonstrates the dominance of the a_1\pi and \omega\pi intermediate states. Upper limits for the contributions of other alternative mechanisms are also placed.Abstract The 5.8 pb −1 of data collected by the CMD-2 Collaboration in the energy range 1.05–1.38 GeV have been used to study energy dependence of the processes e + e − → π + π − 2 π 0 and e + e − →2 π + 2 π − . Analysis of the differential distributions demonstrates the dominance of the a 1 (1260) π and ωπ intermediate states. Upper limits for the contributions of other possible states are also obtained.

Measurement of the Pion Form Factor in the Range 1.04 1.38 GeV with the CMD-2 Detector

The cross section for the process e+e− → π+π− is measured in the c.m. energy range 1.04—1.38 GeV by analyzing 995 000 selected collinear events including 860000 e+e− events, 82000 μ+μ− events, and 33000 π+π− events. The systematic and statistical errors of measuring the pion form factor are equal to 1.2–4.2 and 5–13%, respectively.

Study of the process e+e−→π+π−π+π−π0 with the CMD-2 detector

The process e+e- to pi+ pi- pi+ pi- pi0 has been studied in the center of mass energy range 1280 -- 1380 MeV using 3.0 1/pb of data collected with the CMD-2 detector in Novosibirsk. Analysis shows that the cross section of the five pion production is dominated by the contributions of the eta pi+pi- and omega pi+pi- intermediate states.Abstract The process e+e−→π+π−π+π−π0 has been studied in the center of mass energy range 1280 – 1380 MeV using 3.0 pb−1 of data collected with the CMD-2 detector in Novosibirsk. Analysis shows that the cross section of the five pion production is dominated by the contributions of the ηπ+π− and ωπ+π− intermediate states.

Observation of the φ → π + π − π + π − Decay

Using 11.6 pb^{-1} of data collected in the energy range 0.984--1.06 GeV by CMD-2 at VEPP-2M, the cross section of the reaction e+e- to pi+pi-pi+pi- has been studied. For the first time an interference pattern was observed in the energy dependence of the cross section near the phi meson. The branching ratio of the phi to pi+pi-pi+pi- decay double suppressed by the G-parity and OZI rule is measured Br(phi to pi+pi-pi+pi-) = (3.93 +- 1.74 +- 2.14) \cdot 10^{-6}. The upper limits have been placed for the decays phi to pi+pi-pi+pi-pi0 and phi to eta pi+pi- Br(phi to pi+pi-pi+pi-pi0)<4.6 \cdot 10^{-6} 90% CL, Br(phi to eta pi+pi-)<1.8 \cdot 10^{-5} 90% CL.AbstractUsing 11.6 pb −1 of data collected in the energy range 0.984–1.06GeV by CMD-2 at VEPP-2M, the cross section of the reaction e + e − →π + π − π + π − hasbeen studied. For the firsttime an interference patternwas observed in the energy dependence of the cross section near theφ meson. The branching ratio of the φ → π + π − π + π − decay doublesuppressed by the G-parity and OZI rule is measuredBr(φ → π + π − π + π − ) = (3.93 ±1.74 ±2.14) ·10 −6 .The upper limits have been placed for the decays φ → π + π − π + π − π 0 and φ → ηπ + π − Br(φ → π + π − π + π − π 0 ) < 4.6 ·10 −6 90%CL,Br(φ → ηπ + π − ) < 1.8 ·10 −5 90%CL. 1 Introduction Production of four pions in e + e − annihilation is now well studied in the c.m.energy range 1.05 to 2.5 GeV (see [ 1] and references therein). Results onthe measurements of the cross section of the reaction e + e − → π + π − π + π − in the energy range from 0.60 to 0.97 GeV as well as the probability of theρ 0 meson decay into the π + π − π + π −

Cross section of the reaction e+e- → π+π-π+π- below 1 GeV at CMD-2

Abstract Using 3.07 pb −1 of data collected in the energy range 0.60–0.97 GeV by CMD-2, about 150 events of the process e + e − → π + π − π + π − have been selected. The energy dependence of the cross section agrees with the assumption of the a 1 (1260) π intermediate state which is dominant above 1 GeV. For the first time π + π − π + π − events are observed at the ρ meson energy. Under the assumption that all these events come from the ρ meson decay, the value of the cross section at the ρ meson peak corresponds to the following decay width: Γ(ρ 0 →π + π − π + π − )=(2.8±1.4±0.5) keV or to the branching ratio B(ρ 0 →π + π − π + π − )=(1.8±0.9±0.3)·10 −5 .Using 3.07

Measurement of ω meson parameters in π+π−π0 decay mode with CMD-2

{pb}^{-1}