Measurement of the branching ratios of the Z{sup 0} into heavy quarks

We measure the hadronic branching ratios of the Z{sup 0} boson into heavy quarks: R{sub b}={gamma}{sub Z{sup 0}}{sub {yields}}{sub bb}/{gamma}{sub Z{sup 0}}{sub {yields}}{sub hadrons} and R{sub c}={gamma}{sub Z{sup 0}}{sub {yields}}{sub cc}/{gamma}{sub Z{sup 0}}{sub {yields}}{sub 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})