AN IMPROVED TEST OF THE FLAVOR INDEPENDENCE OF STRONG INTERACTIONS The SLD Collaboration.pdf

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AN IMPROVED TEST OF THE FLAVOR INDEPENDENCE OF STRONG INTERACTIONS The SLD Collaboration.pdf

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AN IMPROVED TEST OF THE FLAVOR INDEPENDENCE OF STRONG INTERACTIONS The SLD Collaboration

SLAC{PUB{7660May 1998AN IMPROVED TEST OFTHE FLAVOR INDEPENDENCE OF STRONGINTERACTIONSThe SLD CollaborationStanford Linear Accelerator CenterStanford University, Stanford, CA 94309ABSTRACTWe present an improved comparison of the strong coupling of the gluon to light (ql = u+d+s),c, and b quarks, determined from multijet rates in avor-tagged samples of hadronic Z0decays recorded with the SLC Large Detector at the SLAC Linear Collider between 1993and 1995. Flavor separation among primary qlql, cc, and bb nal states was made on thebasis of the reconstructed mass of long-lived heavy-hadron decay vertices, yielding tagswith high purity and low bias against 3-jet nal states. We nd: cs=udss = 1:036 0:043 (stat:)+0:0410:045 (syst:)+0:0200:018 (theory) and bs=udss = 1:0040:018 (stat:)+0:0260:031 (syst:)+0:0180:029(theory). To appear in Physical Review D Contributed to the XXIX International Conference on High Energy Physics, Vancouver,B.C. Canada, July 23-29 1998: Parallel sessions 3,7; plenary sessions 4,18.Work supported by Department of Energy contract DE-AC03-76SF00515 (SLAC). 1. IntroductionIn order for Quantum Chromodynamics (QCD) [1] to be a gauge-invariant renormalis-able eld theory it is required that the strong coupling between quarks (q) and gluons(g), s, be independent of quark avor. This basic ansatz can be tested directly in e+eannihilation by measuring the strong coupling in events of the type e+e ! qqg forspecic quark avors. Whereas an absolute determination of s using such a techniqueis limited, primarily by large theoretical uncertainties, to the 5%-level of precision [2],a much more precise test of the avor-independence can be made from the ratio of thecouplings for dierent quark avors, in which most experimental errors and theoreti-cal uncertainties cancel. Furthermore, the emission of gluon radiation in bb events isexpected [3] to be modied relative to that in qlql (ql =u+d+s) events due to the largeb-quark mass, and co