Abstract
The COMPASS experiment at the CERN SPS investigates the structure and spectrum of hadrons by scattering high energetic hadrons and polarised muons off various fixed targets. During the years 2002–2007, COMPASS focused on nucleon spin physics using 160 GeV/c polarised µ+ beams on polarised deuteron and proton targets, including measurements of the gluon contribution to the nucleon spin using longitudinal target polarisation as well as studies of transverse spin effects in the nucleon on a transversely polarised target. One major goal of the physics programme using hadron beams is the search for new states, in particular the search for JPC exotic states and glue-balls. COMPASS measures not only charged but also neutral final-state particles, allowing for investigation of new objects in different reactions and decay channels. In addition COMPASS can measure low-energy QCD constants like, e.g. the electromagnetic polarisability of the pion. Apart from a few days pilot run data taken in 2004 with a 190 GeV/c π− beam on a Pb target, showing a significant spin-exotic JPC = 1−+ resonance at around 1660 MeV/c2, COMPASS collected high statistics with negative and positive 190 GeV/c hadron beams on a proton (H2) and nuclear (Ni, Pb) targets in 2008 and 2009. We give a selected overview of the newest results and discuss the status of various ongoing analyses.
Highlights
The COMPASS fixed-target experiment is a facility to study Quantum Chromodynamics (QCD), covering a large range in momentum transfer from larger than 1 GeV2/c2 down to smaller than 10−3 GeV2/c2
The present mass-independent partial-wave analyses (PWA) results of the search for the π1(1600) in the ρπ decay channel based on the 2008 data is compared for the neutral and the charged 3π decay modes in Fig. 1, left
The PWA model applied is essentially the same as it was used for the published result that is is given for comparison (Fig. 1, right), a short detailed description of the two step PWA method can be found in e.g. [7]
Summary
The COMPASS fixed-target experiment is a facility to study QCD, covering a large range in momentum transfer from larger than 1 GeV2/c2 down to smaller than 10−3 GeV2/c2. One important goal of the physics programme using hadron beams is the search for new states, like spin-exotic mesons and glue-balls Such states are beyond the simple Constituent Quark Model (CQM), they are allowed and even predicted within Quantum Chromodynamics (QCD). The fact that COMPASS measures charged final state particles and neutral particles, like π0, η, and η , is of great advantage, allowing for independent confirmation of new states within the same experiment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
