Measurement of the e+e− → π+π− process cross section with the SND detector at the VEPP-2000 collider in the energy region 0.525 < $$ \sqrt{s} $$ < 0.883 GeV
М. Н. Ачасов, Alexander A. Baykov, A. Barnyakov, K. Beloborodov, A. V. Berdyugin, D. E. Berkaev, A. G. Bogdanchikov, A. A. Botov, T. Dimova, V. P. Druzhinin, В. Б. Голубев, L. Kardapoltsev, A. G. Kharlamov, I. A. Koop, A. A. Korol, D. P. Kovrizhin, A. Kupich, А. П. Лысенко, K. A. Martin, N. A. Melnikova, N. Yu. Muchnoi, A. E. Obrazovsky, Е. В. Пахтусова, E. A. Perevedentsev, К. В. Пугачев, Ya. S. Savchenko, S. I. Serednyakov, З. К. Силагадзе, P. Yu. Shatunov, Yu. M. Shatunov, D. Shtol, D. B. Shwartz, I. K. Surin, Y. Usov, I. M. Zemlyansky, V. N. Zhabin
Abstract
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 < $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> < 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 $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> > 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.