Hadronic Decays of the ω Meson

Uppsala Dissertations from the Facutly of Science & Technology No. 125

By: Lena Heijkenskjold
August 2016
Uppsala University
Distributed by Coronet Books
ISBN: 9789155495947
115 Pages, Illustrated
$45.00 Paper original


Two decay channels of the ω(782) meson, into π+π-π0 and π+π-, are studied. The dynamics of the three-pion channel is represented using a two-dimensional distribution, called a Dalitz plot. A high-statistics Dalitz plot distribution is needed to test theoretical predictions and increase understanding of the decay mechanism. The isospin-breaking two-pion decay gives insight into the ρ-ω mixing. The ω→π+π- decay has previously been studied in π+π- spectra in high statistics e+e- experiments and with lower statistics in hadroproduction experiments. The collected evidence indicates that the resulting interference pattern strongly depends on the production reaction.

In 2011 an experiment to investigate ω hadronic decays in pd→3Heω reaction was performed with the WASA detector. Two studies based on the collected data are included in this thesis. In the first, the dominant decay channel ω→π+π-π0 is selected and two experimental Dalitz plot distributions are created. Each distribution corresponds to one of the two incident beam energies used in the experiment. A fit to the Dalitz plots is performed using a parametrisation including the expected P-wave shape. The result indicates an onset of the intermediate ρ in the two-pion channel, as predicted by theoretical models. The efficiency corrected Dalitz plot bin contents are reported to facilitate comparison to theoretical predictions by direct fits to the experimental data. In the second study, the ω→π+π- decay channel is selected. For events with a 3Heπ+π- final state, the 3He missing mass is constructed in search for the ρ-ω interference pattern in pd production. No significant deviations around the ω mass position was found. Dedicated studies using experimental data to estimate background contribution and to extract signal acceptance shows that the background is too large to observe the expected signal with the collected data sample.

The last part of the thesis presents pre-studies for using data collected at the KLOE detector for an ω→π+π-π0 Dalitz plot analysis. Since the ω mesons are produced in the e+e-→ωπ0 reaction, the study focuses on the impact of the π0-π0 interference.