Measurement of the Branching Ratio of the Z0 into Heavy Quarks

We measure the hadronic branching ratios of the Z{sup 0} boson into heavy quarks: R{sub b} = {Lambda}{sub Z{sup 0}{yields}b{bar b}}/{Lambda}{sub Z{sup 0}{yields}hadrons} and R{sub c} = {Lambda}{sub Z{sup 0}{yields}c{bar c}}/{Lambda}{sub Z{sup 0}{yields}hadrons} using a multitag technique. The measurement was performed using about 400,000 hadronic Z{sup 0} events recorded in the SLC Large Detector experiment at SLAC between 1996 and 1998. The small and stable SLAC Linear Collider beam spot and the CCD-based vertex detector were used to reconstruct bottom and charm hadron decay vertices with high efficiency and purity, which enables us to measure most efficiencies from data. We obtain, R{sub b} = 0.21604 {+-} 0.00098(stat.) {+-} 0.00073(syst.) {-+} 0.00012(R{sub c}) and, R{sub c} = 0.1744 {+-} 0.0031(stat.) {+-} 0.0020(syst.) {-+} 0.0006(R{sub b}).