Dortmund 2006 – wissenschaftliches Programm
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T: Teilchenphysik
T 301: QCD Experiment
T 301.1: Vortrag
Dienstag, 28. März 2006, 16:40–16:55, HG2-HS2
Measurement of exclusive π+ production at HERMES — •Ivana Hristova — DESY, 15738 Zeuthen
Hard exclusive production of π+ mesons is studied at HERMES using 27.6 GeV electron beam and transversely polarised hydrogen target. The single-spin asymmetry and the total cross section are investigated in the kinematic domain defined by 1.5<Q2<10.5 GeV2, 0.02<x<0.8 and −t<0.75 GeV2, whereby ⟨ Q2 ⟩ ≈ 2.0 GeV2, ⟨ x ⟩ ≈ 0.1 and ⟨ −t ⟩ ≈ 0.4 GeV2. The study of this process helps test our understanding of the structure of the nucleon and the production mechanisms of hadrons. This reaction is sensitive in particular to the generalised parton distribution E [1]. At small −t=mπ2, the leading order amplitude is assumed to be dominated by the pion-pole contribution, which is directly related to the pion form factor, thus allowing for modeling of E and quantifying the observable effects [2]. From comparison of the measured and predicted cross section one could study the onset of the hard regime and whether the scattering in the experiment is dominated by longitudinally polarised virtulal photons. The asymmetry, on the other hand, should be rather stable observable since factorisation could take place at moderately high Q2. If E is not zero, the asymmetry is predicted to display a characteristic sinusoidal behaviour with large amplitude [3]. We report on the data analysis and extraction of the asymmetry. The preliminary cross section results are also presented and compared to models.
[1] Phys. Rev. D 56 (1997) 2982.
[2] Eur. Phys. J. C 10 (1999) 307.; Phys. Rev. D 60 (1999) 094017.
[3] Phys. Rev. D 60 (1999) 014010.; Phys. Lett. B 513 (2001) 349.