A Test of the Flavor Independence of Strong Interactions in e⁺e^- Annihilation at the Z⁰ Pole

We present a comparison of the strong couplings of light (u, d, and s), c, and b quarks determined from multijet rates in flavor-tagged samples of hadronic Z decays recorded with the SLC Large Detector at the SLAC Linear Collider. Flavor separation on the basis of lifetime and decay multiplicity differences among hadrons containing light, c, and b quarks was made using the SLD precision tracking system. We find: α s /α all s = 0.987±0.027(stat)± 0.022(syst) ± 0.022(theory), α s/α s = 1.012 ± 0.104 ± 0.102 ± 0.096, and α s/α all s = 1.026 ± 0.041 ± 0.041 ± 0.030. Submitted to Physical Review Letters Work supported in part by Department of Energy contracts: DE–FG02–91ER40676 (BU), DE–FG03– 92ER40701 (CIT), DE–FG03–93ER40788 (CSU), DE–FG02–91ER40672 (Colorado), DE–FG02–91ER40677 (Ill-ınois), DE–AC03-76SF00098 (LBL), DE–FG02–92ER40715 (Massachusetts), DE–AC02–76ER03069 (MIT), DE–FG06–85ER40224 (Oregon), DE–AC03–76SF00515 (SLAC), DE–FG05–91ER40627 (Tennessee), DE–FG03–91ER40618 (UCSB), DE–FG03–92ER40689 (UCSC), DE–AC02–76ER00881 (Wisconsin), DE–FG02–92ER40704 (Yale); by National Science Foundation grants: PHY–89–21320 (Columbia), PHY– 92–04239 (Cincinnati), PHY–88–17930 (Rutgers), PHY–91–13428 (UCSC), PHY–88–19316 (Vanderbilt), PHY–92–03212 (Washington); by the Istituto Nazionale di Fisica Nucleare of Italy (Bologna, Ferrara, Frascati, Pisa, Padova, Perugia); by the Japan-US Cooperative Research Project on High Energy Physics (Nagoya, Tohoku); and by the UK Science and Engineering Research Council (Brunel and RAL). The SLD Collaboration authors and their institutions are listed following the References. A fundamental assumption of the theory of strong interactions, Quantum Chromodynamics (QCD), is that the strong coupling αs is independent of quark flavor. This can be tested by measuring the strong coupling in events of the type ee → qq̄(g) for specific quark flavors q. Although an absolute determination of αs for each quark flavor would have large theoretical uncertainties [1], it is possible to test the flavor-independence of QCD precisely by measuring ratios of couplings in which most experimental errors and theoretical uncertainties are expected to cancel. Since it has recently been suggested [2] that a flavor-dependent anomalous quark chromomagnetic moment could modify the probability for the radiation of gluons, comparison of the strong coupling for different quark flavors may also provide information on physics beyond the Standard Model. Comparisons of αs for b or c quarks with αs for all flavors made at PETRA [3] were limited in precision to ±0.41 (c) and ±0.57 (b) due to small data samples and limited heavy quark tagging capability. LEP measurements of α s/α udsc s have reached precisions between ±0.06 and ±0.02 [4] under the assumption that αs is independent of flavor for all the non-b quarks. The OPAL Collaboration has measured α s/α all s for all five flavors f with no assumption on the relative value of αs for different flavors [5] to precisions of ±0.026 for b and ±0.09 to ±0.20 for the other flavors. The kinematic signatures used to tag c and light quarks suffer from low efficiency and strong biases, due to preferential tagging of events without hard gluon radiation. The SLC Large Detector (SLD) [6] at the SLAC Linear Collider (SLC) is an ideal environment in which to test the flavor independence of strong interactions. tracking capability of the Central Drift Chamber (CDC) [7] and the precision CCD Vertex Detector (VXD) [8], combined with the stable, micron-sized beam interaction point (IP), allows us to select Z → bb(g) and Z → qlq̄l(g) (ql = u, d, s) events using their quark decay lifetime signatures with high efficiency and purity and low bias. Here we present the first precise measurements of α s/α all s , α c s/α all s , and α uds s /α all s using this technique, and making no assumptions about the relative values of α s, α c s and α uds s .