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HK: Physik der Hadronen und Kerne

HK 1: Hauptvortr
äge

HK 1.3: Hauptvortrag

Freitag, 4. März 2005, 10:55–11:25, TU MA001

The COMPASS Experiment at CERN — •Joerg Pretz — CERN/PH, CH 1211 Genf 23

COMPASS is a fixed target experiment at CERN studying the spin structure of the nucleon using a polarized muon beam. Hadron spectroscopy and structure is investigated using hadron beams. The main goal of the muon program is the determination of the gluon helicity contribution, Δ G/G, to the nucleon spin. Previous measurements showed that only a surprisingly small fraction (20-30%) of the nucleon spin originates from the quark helicity contribution. The measurement of Δ G/G will thus help to resolve this so called spin puzzle.

Δ G/G can be accessed by measuring double spin asymmetries of various hadronic final states produced in deep inelastic reactions on a longitudinally polarized nucleon target. COMPASS measures asymmetries of hadrons with large transverse momentum and of charmed mesons. In parallel other physics topics like the measurement of polarized quark distributions and the spin transfer of Λs are studied. Part of the running time was dedicated to the measurement of transverse quark distributions which demands a transversely polarized target.

COMPASS is taking data since 2002 with a muon beam. At the end of the 2004 data taking period a first hadron beam pilot run was performed. Recent results will be presented.