24–29 Aug 2014
Hamburg University
Europe/Berlin timezone

The GPD physics program at COMPASS: present results and future perspectives

26 Aug 2014, 14:40
20m
Hörsaal A (Main Building)

Hörsaal A

Main Building

Talk 2) Quarks and gluons in hadrons, the hadron spectrum Quarks and gluons in hadrons, the hadron spectrum

Speaker

Dr Eric Fuchey (CEA Saclay)

Description

An important component of the physics program at COMPASS (Common Muon Proton Apparatus for Structure and Spectroscopy) is the study of the nucleon structure through generalized parton distributions (GPDs). The GPDs correlate the momentum distributions of the quarks inside the nucleon with a transverse spatial distribution, hence providing a three dimensional imaging of the nucleon. Experimentally, those can be accessed by exclusive processes such as deeply virtual Compton scattering (DVCS), or hard exclusive meson production (HEMP). The study of the hard exclusive processes such as DVCS thanks to muon-proton scattering at COMPASS will provide unique information for the parameterization of the nucleon structure in terms of GPDs. In COMPASS II will be equipped with a 2.5 m liquid hydrogen target, on which will be sent a 160 GeV muon beam with high intensity and high polarization. The resulting kinematic range covered spans from 0.01 < xBj < 0.15 with a Q2 up to 10 GeV2, which yet remains unexplored. In addition to the usual COMPASS setup, a Time-Of-Flight recoil detector is installed to identify the recoiling proton and ensure exclusivity, as well as a new electromagnetic calorimeter to enlarge the photon angular acceptance. The most unique feature of COMPASS is the possibility to receive both mu+ and mu- beams. Measuring the cross section for both beam charge and spin states will grant important additional insight for the extraction of the GPD H. So far, a pilot run of one week with lower luminosity and a prototype recoil detector proved the capability of the COMPASS spectrometer to measure exclusive photon leptoproduction o the proton. The results of this test run will be presented. Later on, a test run of four weeks at nominal luminosity and with the complete proton detector has been recorded, and its analysis is underway. Preliminary results of this run will be presented. Besides DVCS, COMPASS is also capable to measure HEMP, which are particularly interesting for flavour separation in the GPDs extraction. The experiment already provided us with such data, namely mu p -> mu p rho0, which have been analyzed and successfully interpreted in the GPD framework developed by S. Goloskokov and P. Kroll. Those exclusive rho0 results will also be discussed.

Primary author

Dr Eric Fuchey (CEA Saclay)

Presentation materials