Hadron spectroscopy with COMPASS -- First results

TL;DR

The paper reports initial results from the COMPASS experiment at CERN, focusing on light hadron spectroscopy, including the search for exotic states and glueballs, with new data supporting the observation of potential new hadronic states.

Contribution

First results from COMPASS using 2008/09 data, including partial wave analysis and comparison of decay modes, advancing the search for exotic hadrons and glueballs.

Findings

Evidence for an exotic $J^{PC}=1^{-+}$ state at 1.66 GeV/c^2

First comparison of neutral and charged decay modes in diffractive dissociation

Successful partial wave analysis of 2008 data

Abstract

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. After a short pilot run in 2004 (190 GeV/c $\pi^{-}$ beam, Pb target) showing significant production strength of an exotic $J^{PC}=1^{-+}$ state at 1.66\,GeV/${\rm c^2}$, we have collected data with 190 GeV/c hadron beams on a liquid hydrogen target in 2008/09. The spectrometer features good coverage by calorimetry and our data provide excellent opportunity for simultaneous observation of new states in different decay modes. The diffractively produced $(3\pi)^{-}$ system for example can be studied in both modes $\pi^{-}p \rightarrow \pi^{-}\pi^{+}\pi^{-}p$ and $\pi^{-}~p \rightarrow \pi^{-}\pi^{0}\pi^{0}~p$. Reconstruction of charged and neutral mode rely on completely different parts of the apparatus. Observation of new st ates in both modes provides important checks. The results on diffractive dissociation into 3$\pi$ 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.