Diffractive Dissociation into \pi- \pi- \pi+ Final States at COMPASS

TL;DR

This paper reports on diffractive dissociation studies at COMPASS, revealing a significant spin-exotic (1600) resonance and providing detailed meson spectroscopy results from extensive data sets collected with various targets.

Contribution

It presents new high-statistics partial-wave analysis results of (1600) resonance and meson spectra from COMPASS, utilizing upgraded detectors and diverse target materials.

Findings

Observation of a significant spin-exotic (1600) signal.

Comprehensive meson spectrum analysis with 60 million events.

Comparison of final states produced on different target materials.

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 pion beam and a lead target, 420k \pi- \pi- \pi+ final-state events with masses below 2.5 GeV/c2 were recorded, yielding a significant spin-exotic signal for the controversial \pi 1(1600) resonance. After a significant upgrade of the spectrometer in 2007, the following two years were dedicated to meson spectroscopy. Using again a pion beam, but now with a liquid hydrogen target, an unique statistics of ~60M events of the same final state was gathered in 2008. During a short campaign in 2009, the H2 target was exchanged by several solid state targets in order to compare final states produced on targets with different atomic numbers. A partial-wave Analysis (PWA) was performed on all these data sets and results are presented.