We study the X-ray and optical properties of 16 Broad Absorption Line ( BAL ) quasars detected in a \approx 3 deg ^ { 2 } region common to the wide synoptic ( W-1 ) component of the Canada - France - Hawaii Telescope Legacy Survey ( CFHTLS ) and the XMM Large Scale Structure survey ( XMM-LSS ) .
The BAL fraction is found to be 10 % in full sample , 7 % for the optical colour selected QSOs and as high as 33 % if we consider QSOs selected from their IR colours .
The X-ray detected non-BAL and BAL quasars have a mean observed X-ray-to-optical spectral slope ( \alpha _ { ox } ) of - 1.47 \pm 0.13 and - 1.66 \pm 0.17 respectively .
We also find that the BAL QSOs have \alpha _ { ox } systematically smaller than what is expected from the relationship between optical luminosity and \alpha _ { ox } as derived from our sample .
Based on this , we show , as already reported in the literature for quasars with high optical luminosities , our new sample of BAL QSOs have X-ray luminosity a factor of three smaller than what has been found for non-BAL QSOs with similar optical luminosities .
Comparison of hardness ratio of the BAL and non-BAL QSOs suggests a possible soft X-ray weakness of BAL QSOs .
Combining our sample , of relatively fainter QSOs , with others from the literature we show that larger balnicity index ( BI ) and maximum velocity ( V _ { max } ) of the C iv absorption are correlated with steeper X-ray to optical spectral index .
We argue that this is most likely a consequence of the existence of a lower envelope in the distribution of BI ( or V _ { max } ) values versus optical luminosity .
Our results thus show that the previously known X-ray weakness of BAL QSOs extends to lower optical luminosities as well .