München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 28: Elektromagnetische und Hadronische Sonden

HK 28.7: Vortrag

Mittwoch, 22. März 2006, 15:30–15:45, F

Exclusive $rho^0$ Production at HERMES — •Armine Rostomyan — HERMES / DESY, Notkestrasse 85, 22607,Hamburg

The measurement of hard exclusive processes opens access to the unknown Generalized Parton Distributions (GPDs) of the nucleon which provide an unified description of hadronic structure. Moreover, it was shown that the first moment of the GPDs H and E can be related to the total angular momentum of the quarks inside the nucleon.

This talk will report on measurements of hard exclusive $∖rho^0$ production on a hydrogen target at HERMES using the 27.6 GeV HERA positron beam. First preliminary result for the single target-spin asymmetry measured with a transversely polarised hydrogen target will be presented.

Using the measured spin density matrix elements, representing the helicity transfer from the virtual photon to the $rho^0$ mesons, the ratio of the longitudinal to transverse components of the production cross section is determined. The extracted longitudinal part of the total cross section will be compared to GPD calculations.

It has been predicted that the transverse spin asymmetry depends linearly on the GPD E and, therefore, provides an unique observable for obtaining constraints on E.