2011/07/31 by P. Adlarson, C. Adolph, W. Augustyniak +136 · 45 citations
Mathematics · Physics and Astronomy · #Algorithm #High-Energy Particle Collisions Research #Mathematics #Meson #Particle physics #Particle physics theoretical and experimental studies #Physics #Pion #Quantum Chromodynamics and Particle Interactions #hep-ex #nucl-ex
paper · pdf · doi:10.1016/j.physletb.2011.12.027
published in Physics Letters B 707(2), 243-249 (Elsevier BV) · 7 pages, 10 figures, submitted to Phys.Lett.B
arxiv created 2011/11/17 · openalex publication_date 2011/12/16 · arxiv updated 2015/03/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
An exclusive measurement of the decay eta --> pi+ pi- gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd --> 3He X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13340±140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta --> pi+ pi- gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi+ pi- system.