Context :

Aims : We present a cosmic shear analysis and data validation of 15 square degree high-quality R -band data of the Garching-Bonn Deep Survey obtained with the Wide Field Imager of the MPG/ESO 2.2m telescope .

Methods : We measure the two-point shear correlation functions to calculate the aperture mass dispersion .
Both statistics are used to perform the data quality control .
Combining the cosmic shear signal with a photometric redshift distribution of a galaxy sub-sample obtained from two square degree of UBVRI -band observations of the Deep Public Survey we determine constraints for the matter density \Omega _ { m } , the mass power spectrum normalisation \sigma _ { 8 } and the dark energy density \Omega _ { \Lambda } in the magnitude interval R \in [ 21.5 , 24.5 ] .
In this magnitude interval the effective number density of source galaxies is n = 12.5 { arcmin } ^ { -2 } , and their mean redshift is \bar { z } = 0.78 .
To estimate the posterior likelihood we employ the Monte Carlo Markov Chain method .

Results : Using the aperture mass dispersion we obtain for the mass power spectrum normalisation \sigma _ { 8 } = 0.80 \pm 0.10 ( 1 \sigma statistical error ) at a fixed matter density \Omega _ { m } = 0.30 assuming a flat universe with negligible baryon content and marginalising over the Hubble parameter and the uncertainties in the fitted redshift distribution .

Conclusions :