Diffractive Dissociation into π[sup −]π[sup −]π[sup +] Final States at COMPASS

Abstract

Diffractive dissociation reactions studied at the COMPASS experiment at CERN provide access to the light-meson spectrum. During a pilot run in 2004, using a negative pion beam and a Pb target, 420k π − π − π + final-state events with masses below 2.5 GeV/c 2 were recorded, yielding a significant spin-exotic signal for the controversial π 1 (1600) resonance. After a major upgrade of the spectrometer in 2007, the following two years were dedicated to hadron spectroscopy.Using again a pion beam, but now with a liquid hydrogen target, a unique statistics of ∼60M events of the 3π final state was gathered in 2008. During a short campaign in 2009, the H 2 target was replaced by several solid state targets in order to study the effect of the target material on the production. A partial-wave analysis (PWA) was performed on all these data sets and results are presented.