Measurement of the e+e−→ ηπ+π− cross section with the CMD-3 detector at the VEPP-2000 collider

Abstract

The cross section of the process e + e − → ηπ + π − is measured using the data collected with the CMD-3 detector at the VEPP-2000 collider in the center-of-mass energy range from 1.1 to 2.0 GeV. The decay mode η → γγ is used for η meson reconstruction in the data sample corresponding to an integrated luminosity of 78.3 pb −1. The energy dependence of the e + e − → ηπ + π − cross section is fitted within the framework of vector meson dominance in order to extract the Γ(ρ(1450) → e + e −)B(ρ(1450) → ηπ + π −) and the Γ(ρ(1700) → e + e −)B(ρ(1700) → ηπ + π −) products. Based on conservation of vector current, the analyzed data are used to test the relationship between the e + e − → ηπ + π − cross section and the spectral function in τ − → ηπ − π 0 ν τ decay. The e + e − → ηπ + π − cross section obtained with the CMD-3 detector is in good agreement with the previous measurements.

Two and three pseudoscalar production in e+e− annihilation and their contributions to (g − 2)μ

“…The experimental data displayed for e + e − → πππ are from DM1 [97], ND [98], DM2 [99], CMD2 [100][101][102], SND [63,103,104], Babar [105], and BESIII [64]. The experimental data displayed for e + e − → ππη are from DM2 [106], ND [98], CMD2 [107], Babar [108], SND [65,66,109], and CMD3 [67].…”

“…SND also measured e + e − → ηππ channel with η in η → γγ mode [65] and η → 3π 0 mode [66], and a combined results of these two modes were provided in [66]. CMD3 [67] also measured e + e − → ηππ in η → γγ mode, and the cross section values combined with its previous measurements were provided. Very recently, BESIII measured e + e − → η ππ above 2 GeV [68].…”

Strong coupling from an improved τ vector isovector spectral function

“…We have recently produced a new vector isovector spectral function based on a combination of the ALEPH and OPAL spectra for the dominant ππ 0 , π3π 0 , and 3ππ 0 τ decay channels, supplemented by the addition of contributions from all numerically significant residual decay modes. The residual modes contributions are obtained entirely from experimental data, using the recent BaBAR spectrum for τ → K − K 0 ν τ [14] and a wealth of recent CVC-related cross-section results from e + e − → hadrons obtained by CMD-3, SND and BaBar [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. This new spectral function is more inclusive than its predecessors, since it contains more residual modes, is solely based on experimental data (with no Monte Carlo simulated channels), and has smaller errors.…”

“…We include, in our new spectral function, the following decay modes: (i) π − ω(→ non-3π), K − K 0 , ηπ − π 0 , K Kπ, 3π − 2π + π 0 , and 2π − π + 3π 0 , which were also included by both the ALEPH and OPAL collaborations, (ii) (3π) − ω(→ non-3π) and K Kππ, included only by ALEPH, and (iii) the small additional contributions from π − 5π 0 and ηωπ + η4π, not included in either of the ALEPH or OPAL analyses. With the exception of the contributions from τ → K − K 0 ν τ , which were measured by BaBar [14], all the other modes are obtained from the respective e + e − cross sections with CVC [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], applying the necessary corrections for vacuum polarization effects. The individual channels are normalized to the respective BFs described in the 2019 HFLAV compilation [32] (correlations among these values are taken into account).…”

A new method for obtaining a Born cross section using visible cross section data from e+e− colliders

“…To describe the dependence of the e + e − → ηπ + π − Born cross section on the c.m. energy, the function and parameters from the work [28] are used. The corresponding model Born cross section is shown in figure 5a as a solid curve.…”