New results on the search for spin-exotic mesons with COMPASS

Abstract

The COMPASS fixed-target experiment at the CERN-SPS studies the structure and spectrum of hadrons. One important goal using hadron beams is the search for new states, in particular spin-exotic mesons and glueballs. As a first input to the puzzle, COMPASS observed a significant $J^{PC}$ spin-exotic signal in the 2004 pilot run data (190\,GeV/$c$ $\pi^{-}$ beam, Pb target) in three charged pion final states consistent with the disputed $\pi_1(1600)$. We started our hadron spectroscopy programme in 2008 by collecting very high statistics using a 190 GeV/$c$ negative pion beam scattered off a liquid hydrogen (proton) target. The current status and new results from the 2008 data on the search for the $\pi_1(1600)$ resonance with exotic $J^{PC}=1^{-+}$ quantum numbers obtained from partial-wave analyses of the $\rho\pi$ and $\eta'\pi$ decay channels are presented.