Performance of the b-jet identification in CMS

Jets from bottom quarks are identified by dedicated algorithms in CMS which exploit the high mass and long lifetime of b hadrons. The b-tagging efficiency is measured from events enriched with jets from semimuonic b-hadron decays; events from top-antitop production are also highly enriched in b jets and provide an independent cross-check. The mis-identification rate due to light flavour jets is obtained from inclusive jet studies. Data collected in pp collisions at $\sqrt{s}$ = 7~TeV for an integrated luminosity of 0.50 to 0.89\fbinv are compared to the simulation. The results are presented as data-to-simulation efficiency ratios as a function of the jet transverse momentum, \pt, and pseudorapidity. Data and simulation are found to be in good agreement. The relative uncertainty on the b-tagging efficiency ratio is 10\% for b jets with \pt up to about 200\GeV. The corresponding relative uncertainty on mis-identification is 10\% to 20\% for light flavour jets with \pt up to about 500\GeV.