J. Bernhard

Study of central production of charged pionic modes at COMPASS

The COmmon Muon and Proton Apparatus for Structure and Spectroscopy is a fixed target experiment at the CERN SPS accelerator. In the years 2008 and 2009 the collaboration focused on hadron spectroscopy: data with hadronic beams at a momentum of 190 GeV/c impinging on hydrogen, lead, nickel and tungsten targets were taken. In the preparation for this run‐time, the apparatus was adapted to measure the formation of resonances by both diffractive scattering and central production. In the latter case, the study of charged pionic channels is well‐suited to search for members of the f0 particle family, including some of the glueball candidates. The analysis of the newly taken data has started, these proceedings are meant to give a status and overview of the current activities.

Operational Experience With the Combined Solenoid/Dipole Magnet System of the COMPASS Experiment at CERN

Polarized Drell–Yan measurements require a strong homogeneous magnetic field. A 2.5 T longitudinal field is generated with a superconducting solenoid carrying a nominal current of 650 A, while high homogeneity is obtained by using additional shim—and compensation coils. Since the target needs to be transversely polarized, a second main coil is required. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. Field rotation, from longitudinal to transverse and vice versa, is possible by simultaneously powering both coils. During the complete procedure, the absolute field strength is never allowed to drop below 0.48 T to guarantee a high polarization percentage. In the meantime, the forces between the coils need to be controlled, and therefore the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. In this paper, the magnet system is described and a summary of the operational experience gained during data taking is provided.

Test of the OZI rule in vector meson production with the COMPASS experiment

The COMPASS experiment at CERN collected a large set of data with hadron beams (p, π K) and different targets (H2, Pb, Ni, W) in the years 2008 and 2009. The main goal is the search for exotic bound states of quarks and gluons (glueballs, hybrids) and several preliminary results from the ongoing analysis have already emerged. The production of exotic states is known to be favoured in glue-rich environments, e.g. so-called OZI-forbidden processes. The Okubo-Zweig-Iizuka (OZI) rule states that processes with disconnected quark line diagrams are suppressed. As a consequence, states with an s component should be suppressed with respect to states containing mainly u and d quarks. The numerous reported violations of the OZI rule show that the underlying physics is more complicated. By studying the degree of OZI violation a lot can learned about the production mechanism and possibly also about the nucleon structure itself. The uniquely large COMPASS data sample allows for detailed studies with respect to kinematic variables (e.g. xF). Results from the ongoing analysis on the comparison of ω and vector mesons production in pp → pp (ω/) are presented and an outlook on the prospect of spin alignment measurements with COMPASS is given.