Measurement of the strong coupling constant αS for bottom quarks at the Z0 resonance

Abstract

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 12 May 2018Physics Letters B 271 ( 1991 ) We have measured the ratio of the strong coupling constants as for bottom quarks and light quarks at the Z ° resonance, in order to test the flavour independence of the strong interaction. The coupling strength oq has been determined from the fraction of events with three jets, measured for a sample of all hadronic events, and for inclusive muon and electron events. The b purity is evaluated to be 22% for the first data set and 87% for the inclusive lepton sample. We find cq(b)/as(udsc)=l.O0+ 0.05 (stat.) + 0.06 (syst.).

QCD effects and b -tagging at LEP I

“…Then there will be roughly 4 × 10 4 four jet events with two tagged b-quarks (using the JADE scheme with y cut = 0.01, as in figs. [3][4][5][6]. This is an order of magnitude less than the total number of four jet events, but in return we gain greater power to discriminate between the various terms in the four jet cross section, particularly between the Abelian, QED-like term and the non-Abelian term in the two quark, two gluon cross section.…”

“…Important results have been achieved. The strong coupling constant α s has been determined from jet rates and from shape variables [2] and both the flavour independence [3] and the running with √ s [4] have been verified. Three- [5] and four-jet [6] distributions have been studied and their behaviour agrees with QCD predictions calculated to second order in α s .…”

“…In Z 0 → qqgg events the lowest energy parton is a gluon in ≈ 84% of cases, whereas the percentage of events in which the two lowest energy partons are both gluons is only ≈ 53%[14] 3. An updated review on matrix element computations for multi-jet production in e + e − reactions presented in the literature can be found, e.g., in the introduction of ref [23]…”

Next-to-leading order QCD corrections to three-jet rates with massive quarks

“…In fact b quark mass effects in jets produced at the Z resonance have already been seen indirectly in the so-called "flavour-independence tests" of the strong coupling. Such tests have been performed both at LEP [1] and at SLC [2].…”

Three-jet production at LEP and the bottom quark mass

“…The high precision achieved at LEP makes these effects relevant. In fact, they have to be taken into account in the test of the flavour independence of α s (m Z ) [1][2][3][4][5]. In particular it has been shown [6] that the biggest systematic error in the measurement of α b s (m Z ) (α s obtained from bb-production at LEP from the ratio of three to two jets) comes from the uncertainties in the estimate of the quark mass effects.…”