CERN EP Seminar (up to 2008)

New Results from the COMPASS Experiment


500-1-001 - Main Auditorium (CERN)

500-1-001 - Main Auditorium


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COMPASS is a fixed-target experiment located at the M2 beam line at CERN's super proton synchrotron. The spectrometer has been designed to address a large range of physics topics with hadron and muon beams. Given that no hadron data has been collected yet the presentation will focus on the physics program with the polarized muon beam.

The main objective of this program is to study the spin structure of the nucleon, i.e. to determine how the nucleon spin is shared among its constituents. In analogy to the unpolarized case deep inelastic scattering of polarized leptons off polarized nucleon targets provides access to the polarizations of quarks and gluons.

Triggered by the discovery of EMC at CERN in 1988, that the spin contribution of the quarks is small, a series of experiments at CERN, DESY and SLAC measured this contribution more precisely and found that in fact only about 30% of the nucleon spin is carried by quarks. Consequently a second generation of experiments has been started to search for the missing 70% of the nucleon spin. These experiments concentrate on the determination of the gluon polarisation ΔG/G. At COMPASS this quantity can be measured directly via the so-called photon-gluon fusion process.

COMPASS has started to take data with a 160 GeV muon beam and a polarized deuteron target in 2002 and has since then collected three years of data in this configuration. First physics results from 2002 and 2003 data - including the first determination of ΔG/G by COMPASS - will be presented.

Organiser(s): Christoph Amelung / PH-EP

Note: Tea & coffee will be served at 16.00 hrs.