Absolute Calibration of Luminosity Measurement at CMS: Summer 2011 Update

Luminosity calibration results based on Van der Meer scans conducted in May and June of 2011 are presented. A systematic scale uncertainty of 4.5\% is estimated. For 2011 running prior to August 2011, where the instantaneous per-bunch luminosity was typically 1~Hz/$\mu$b, a scale non-linearity of 7.6\% was observed. An afterglow correction resulting from leakage from collisions in earlier bunches ranges up to $2.5\%$, depending on the filling pattern for the LHC. Luminosity results used as input to CMS analyses are corrected for both scale non-linearity and afterglow in a run-dependent way. Taking all corrections into account results in an upward correction of 5\% with respect to the values reported online for the typical 2011 run.