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    PR # 31283                                                                   
     The origin of the Cosmic X-ray Background(CXB) is still now an open q       
     uestion in the X-ray astronomy. Previous observations in soft X-ray b       
     and have resolved more than half of the CXB flux to known classes of        
     objects such as AGNs and QSOs, while there sill remains a significant       
      part of the CXB flux unresolved whose constituents may be unknown X-       
     ray sources. We propose short exposure observations of deep optical s       
     urvey fields where we have well calibrated optical catalogs, and to t       
     ake cross-correlations of measured X-ray flux distributions to variou       
     s color-selected subsets of optical objects. Our Monte-Carlo simulati       
     on indicate that with 20ksec effective exposure we can detect a corre       
     lation signal with high confidence(>99%) if selected subset is contri       
    buting to the CXB flux signifi                                               
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