Hadron spectroscopy with COMPASS – First results

for the COMPASS collaboration The COMPASS experiment at CERN is dedicated to light hadron spectroscopy with emphasis on the detection of new states, in particular the search for spin exotic states and glueballs. Af-ter a short pilot run in 2004 (190 GeV/c pi − beam, Pb target) showing significant production strength of an exotic JPC = 1−+ state at 1.66 GeV/c2, we have collected data with 190 GeV/c hadron beams on a liquid hydrogen target in 2008/09. The spectrometer features good cover-age by calorimetry and our data provide excellent opportunity for simultaneous observation of new states in different decay modes. The diffractively produced (3pi) − system for example can be studied in both modes pi−p → pi−pi+pi−p and pi − p → pi−pi0pi0 p. Reconstruction of charged and neutral mode rely on completely different parts of the apparatus. Observation of new states in both modes provides important checks. The results on diffractive dissociation into 3pi final states from the 2004 data recently published are discussed as well as the first comparison of neutral vs. charged mode based on a first partial wave analysis of 2008 data.