Study of the process e+e−→ηγ in c.m. energy range 600–1380 MeV at CMD-2

Abstract

The cross section of the process e + e − → ηγ has been measured in the 600-1380 MeV c.m. energy range with the CMD-2 detector. The following branching ratios have been determined: B(ρ → ηγ) = (3.28 ± 0.37 ± 0.23) · 10 −4 , B(ω → ηγ) = (5.10 ± 0.72 ± 0.34) · 10 −4 , B(φ → ηγ) = (1.287 ± 0.013 ± 0.063) · 10 −2 .Evidence for the ρ(1450) → ηγ decay has been obtained for the first time.

Recent results from CMS-2 and SND experiments at VEPP-2M

“…1(a) SND has completed its analysis of the annihilation into π 0 γ and ηγ. Figure 1(b) shows the cross section of the process e + e − → π 0 γ while in Table 2 their results are compared to the previous world best coming from the CMD-2 detector [6]. SND results are consistent with those from CMD-2 and have higher accuracy.…”

Study of thee+e−→ηγprocess with Spherical Neutral Detector at the VEPP-2Me+e−Ачасов1, Aulchenko2, Beloborodov3 et al. 2006Phys. Rev. D272130View full textAdd to dashboardCite

“…The best accuracy in measurement of the decay probabilities ρ, ω, φ → ηγ was achieved in the last e + e − storage ring experiments with CMD-2 [10,11,12] and SND [13,14,15,16,17] detectors through investigation of the e + e − → ρ, ω, φ → ηγ processes. The reached accuracy is of the order of 10% for the decays ρ, ω → ηγ and about 2% for the φ → ηγ decay, and the last result has been obtained by averaging more than 10 measurements with accuracies of the order of 5% each.…”

Reanalysis of thee+e−→ηγreaction cross section

“…Since for the solution corresponding to the ϕ ρ ′ = 180 • the value of ϕ φ differs from its expectation by more than 3.5σ, for our final result we take the solution corresponding to φ ρ ′ = 0 • . It should be noted that the same choice of the ρ ′ phase was used in the work [4].Using the world-average values [10] for the ρ, ω, and φ masses and ρ, ω, φ → e + e − decay probabilities, we can calculate the following values for the decay probabilities into the ηγ final state:B(ρ → ηγ) = (2.82 ± 0.30 ± 0.17) × 10 −4 , B(ω → ηγ) = (4.33 ± 0.44 ± 0.17) × 10 −4 , …”

“…The cross section value in the ρ ′ -resonance maximum obtained from the approximation of the e + e − → ηρ cross section can be translated to the e + e − → ρ ′ → ηγ cross section using VDM as in Ref. [4]. The approximation of the data on the e + e − → ηρ cross section was done with three different models describing the energy dependence of the ρ ′ resonance width:…”

“…Since for the solution corresponding to the ϕ ρ ′ = 180 • the value of ϕ φ differs from its expectation by more than 3.5σ, for our final result we take the solution corresponding to φ ρ ′ = 0 • . It should be noted that the same choice of the ρ ′ phase was used in the work [4].…”