Abstract
An exclusive measurement of the decay η→π +π -γ has been performed at the WASA facility at COSY. The η mesons were produced in the fusion reaction pd→He3 X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13960±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 η→π +π -γ. 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 π +π - system.
Original language | English |
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Pages (from-to) | 243-249 |
Number of pages | 7 |
Journal | Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics |
Volume | 707 |
Issue number | 2 |
DOIs | |
Publication status | Published - 20 Jan 2012 |
Keywords
- η meson
- Box anomaly
- Exclusive measurement