Diffractive Dissociation into Three-Pion Final States at COMPASS

Abstract

In order to study diffractive dissociation reactions, COMPASS has taken data with a 190GeV/c pion beam impinging on a liquid hydrogen target in 2008 and 2009. At squared four-momentum transfers to the target t ′ between 0.1GeV2/c2 and 1.0GeV2/c2 the number of events with three pions in the final state is about an order of magnitude larger than that acquired by any previous experiment. In COMPASS, the three-pion final state can be studied in the two channels π−π−π+ and π−π0π0. The large data sample in particular for the π−π−π+ channel allows to find even small signals at the sub-percent level. The progress of the partial-wave analysis will be shown. Compared to previous COMPASS results, the analysis is now performed in bins of t ′, and the set of partial waves has been extended now including waves up to spin 6. The information from the t ′ dependence of the individual partial waves is very helpful in separating resonant and non-resonant contributions. As a consistency check results from the π−π−π+ channel will be compared to the π−π0π0 channel.