Radiative gluon effects in massive quark-antiquark production in collisions of positrons and polarized electrons at theZ0resonance

Abstract

Cross sections and asymmetries for massive quark-antiquark production in electron-positron collisions at the Z0 resonance are calculated, for the case of longitudinally polarized electrons. The polarization of z', P Z o , for the initial electron polarization P-is composed of P-and the "natural" polarization P Z o (0) = -2av/(v2 + a 2 ) , and the composition rule for polarization is given. The cross section differential in the quark emission polar angle 8 is obtained in terms of form factors which are given as functions of the quark mass m f in exact form. Convenient expansions to order m2f are found and compared to previously published results. For the asymmetries the 2' polarization plays an important role. It is shown that for the forward-backward quark asymmetry AFB(P-) and the forward-backward left-right asymmetry AFB,LR(P-) the quark dependence is the same including radiative corrections, with the relations AFB (P-) : AFB(O) : AFB,LR(P-) = PZo(P-) : PZo(0) : P-. PACS number(s): 13.65.+i, 13.10.+q, 13.87.-a, 13.88.+e

Second order QCD corrections to the forward-backward asymmetry in e+e−-collisions

“…Finally notice that these additional contributions, denoted by F QCD above, only show up in order α 2 s . Moreover if we put m = 0 they only appear in the forward-backward asymmetry (9) but cancel between numerator and denominator in the shape coefficient (10). The results for f l,(2) k follow from the transverse and longitudinal coefficient functions calculated in [16] and the asymmetry coefficient function computed in [17].…”

“…The NLO contributions have been calculated by several groups in the literature for the case m = 0 (see [7]- [10]). However there were some discrepancies between the results so that we decided to calculate them again using a different method.…”

Direct Measurement ofAbinZ0Decays Using Charged Kaon Tagging

“…In order to make the treatment of QCD corrections consistent with other direct measurements of A b from SLD [2], which take the effect of b-quark mass into account at leading order [14], a correction of 20.5% is applied, resulting in a measurement of A b 0.855 6 0.088 stat .…”

A Preliminary Direct Measurement of the Parity-Violating Coupling of the Z{sup 0} to Strange Quarks, A{sub s}

“…f f)= (Z 0 ! hadrons) and the tagging eciencies f ; = 0:013 corrects for the eects of hard gluon radiation [19]; a f denotes the analyzing power for tagging the f rather than the f direction; and A f is the coupling parameter for avor f. The parameters c , b , and a c , a b for the heavy avors are taken from the Monte Carlo simulation [16] since a number of independent measurements lead us to believe these parameters to be reliable within well dened uncertainties. The world average experimental measurements of the parameters A c , A b , R c , R b [1] were used.…”