Study of the process e+e-→π+π-γ with the CMD-3 detector at the e+e- collider VEPP-2000

С С Толмачев ,P Yu Shatunov,E P Solodov,D B Shwartz,Yu M Shatunov,A N Kirpotin,Yu V Yudinl,A V Anisenkov,L.b Epshteyn ,Alexei Talyshev ,A Korobov ,A.v Bragin ,V.s Okhapkin ,I A Koop,S.s Gribanov ,E A Kozyrev,P Lukin ,I M Zemlyansky,N.m Ryskulov ,R.r Akhmetshin ,A.a Grebenuk ,F.v Ignatov ,A.l Erofeev ,V Shebalin ,Г В Федотович ,A Kuzmin ,P Krokovny ,V.sh Banzarov ,V Aulchenko ,A.e Ryzhenenkov ,A.e Kuzmenko ,D.n Grigoriev ,N.s Bashtovoy ,А.і Воробйов ,Y Pestov ,D E Berkaev,K Mikhailov ,В Л Иванов ,D.n Shemyakin ,G.p Razuvaev ,S V Karpov,А С Попов ,В Ф Казанин ,В.м Титов ,A Sibidanov ,A Semenov ,D Epifanov ,S Eidelman ,А.а Рубан ,A.n Amirkhanov ,Aleksei Kozyrev ,B Shwartz ,S.e Gayazov ,A Bondar ,I.b Logashenko

doi:10.1051/epjconf/201921204012

Abstract

Existing Monte-Carlo generators with radiative corrections to the e+e-→π+π- process are usually developed under the assumption that pions can be treated as pointlike particles. We study the e+e-→π+π-γ process with final-state radiation and test this assumption using simulated events from the MCGPJ generator based on the scalar QED hypothesis. In order to increase a fraction of events with FSR, the analysis was performed in the energy region to the left from the ρ-meson peak (660÷785 MeV) that is based on the integrated luminosity of about 8.4 pb-1. The experimental data for the photon energy spectrum agree with the simulation results at 1% level.

Highlights

The physics program of experiments with the CMD-3 includes precise measurements of the cross sections of the e e hadrons processes [1]
In this work we study the e e + process with photon radiation from the final state and test the hypothesis about pointlike pions used in the
Initial particles radiate mainly into a narrow cone along the particle movement path, but about 10% of the photons are emitted at the large angle, it is impossible to separate events with radiation from the initial state from events with radiation from the final state based on the photon angular distribution

Summary

Introduction

The physics program of experiments with the CMD-3 includes precise measurements of the cross sections of the e e hadrons processes [1] Such experiments are necessary, e.g., for the calculation of the hadronic contribution ( had) to the anomalous magnetic moment of the muon ( =(g 2)/2). In this work we study the e e + process with photon radiation from the final state and test the hypothesis about pointlike pions used in the. The study of the e e + process in this energy region allows an increase of the relative fraction of events with the radiation from the final state. For the test of the assumption about pointlike pions we analyzed an experimental photon-energy spectrum and compared it with the simulated one, which we produced using

CMD-3 detector and dataset

Preliminary selection

Background suppression

Data-MC comparison

Findings

Summary