Application Of The Maximum Conformal Principle To The Physical Process Of Top Quark Decay And Bottom Quark

The decay of the top quark and the forward-backward asymmetry of the bottom quark exist in the problem of integral divergence in the perturbation of higherorder calculations.Renormalization theory is used to eliminate divergence.Renormalization theory in the case of infinite order,the prediction of perturbative QCD is independent of the choice of renormalization scheme and scale.Due to the limited computing power at present,it can only be calculated to a limited order,and the theoretical predictions obtained are related to the choice of the renormalization scheme and scale.The conventional renormalization scale selection method conjectures that the renormalization scale is the typical momentum transfer of the studied process,and changes the scale within a certain range to estimate the uncertainty of the scale.The obtained theoretical predictions depend on the renormalization scheme and scale.In 2012,the principle of maximum conformality(PMC)was proposed.PMC strictly eliminates the uncertainty of the renormalization scale and the scheme existing in the conventional method.PMC starts from the renormalization group and satisfies the self-consistent condition of the scale setting method.The PMC method absorbs the non-conformal terms related to the renormalization group into the coupling constant,and the result obtained is independent of the choice of renormalization scheme and scale,thereby improving the accuracy of theoretical predictions.Applying PMC to the top quark decay process and the b quark forward-backward asymmetry process,the main research results are as follows:After applying the PMC method to the top quark decay process,the PMC single scale Q*is determined by absorbing the non-conformal term,so that the top quark decay width is ?ttot=1.3112±0.0016±0.0023GeV,which does not depend on the choice of scale and scheme,theoretical predictions are consistent with current experimental measurements.For the bottom quark forward-backward asymmetry,the result obtained after PMC is AFB0,b=0.1004±0.0016,which reduces the deviation between the theoretical prediction and the experimental value from 2.9? to 2.1?,making the theoretical prediction and the experimental measurement value more consistent.The determined PMC scale is much smaller than the scale predicted by conventional methods,and the convergence of the perturbation series expansion is better,which can achieve more accurate SM prediction and constraining possible new physics.