Meson spectroscopy with COMPASS

TL;DR

The COMPASS experiment at CERN has collected extensive data to study hadron structure, focusing on detecting new states like exotic mesons and glueballs, with initial results indicating a significant exotic signal.

Contribution

This paper reports on the large-scale data collection and analysis efforts of the COMPASS experiment to identify new hadronic states, including the first observation of a potential exotic meson signal.

Findings

Observation of a significant $J^{PC}$ exotic signal consistent with $ ext{pi}_1(1600)$

High-statistics data collection with hadron beams at 190 GeV/c

Ongoing analyses of various final states and exotic meson candidates

Abstract

The COMPASS fixed-target experiment at CERN SPS is dedicated to the study of hadron structure and dynamics. In the physics programme using hadron beams, the focus is on the detection of new states, in particular the search for $J^{PC}$ exotic states and glueballs. After a short pilot run in 2004 (190 GeV/c negative pion beam, lead target), we started our hadron spectroscopy programme in 2008 by collecting an unprecedented statistics with a negative hadron beam (190 GeV/c) on a liquid hydrogen target. A similar amount of data with positive hadron beam (190 GeV/c) has been taken in 2009, as well as some additional data with negative beam on nuclear targets. The spectrometer features a large angular acceptance and high momentum resolution and also good coverage by electromagnetic calorimetry, crucial for the detection of final states involving $\pi^0$ or $\eta$. A first important result is the observation of a significant $J^{PC}$ spin exotic signal consistent with the disputed $\pi_1(1600)$ in the pilot run data. This result was recently published. We present an overview of the status of various ongoing analyses on the 2008/09 data.