RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Working group 2009c giving mt 1731 06stat 11syst

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: t al. (2008). Both of these include a subset of the measurements listed. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 B. W helicity from top-quark decays In the SM, top quarks decay with a V À A interaction through the process t ! W þ b with Bðt ! W þ bÞ % 1. The SM predicts a fraction f0 ¼ 0:697 Æ 0:012 of top-quark decays gives a longitudinally polarized W and a fraction fþ ¼ 3:6  10À4 gives a right-handed W . This leaves fÀ ¼ 1 À f0 À fþ giving left-handed W s. Compared to the decay of lower mass quarks, the fraction of decays with longitudinally polarized W is significantly increased because of the large Yukawa coupling between the top quark and Higgs boson. Changes to the Lorentz (V À A) structure of the decay will result in changed values for the polarization fractions. Indirect results from b ! s measurements (Cho and Misiak, 1994; Fujikawa and Yamada, 1994) constrain fþ to less than a few percent. The angular distribution of the electron-type (I3 ¼ À1=2) W decay product in t ! Wb is given by !ðcÞ ¼ 3½2ð1 À c2 Þf0 þ ð1 À cÞ2 fÀ þ ð1 þ cÞ2 fþ Š 8 all jets, CDF [k] 160 For this combination, which includes preliminary results, the systematic uncertainty is significantly larger than the statistical uncertainty. The dominant components of the systematic uncertainty arise from uncertainty on the in situ jet energy " calibration, uncertainty related to the tt production and decay model, and uncertainty arising for color recombination. These contribute 0.48, 0.49, and 0:41 GeV=c2 to the uncertainty, respectively. An alternative method of measuring the top-quark mass makes use of the dependence of the production cross section on the mass. The top-quark MS mass may be extracted directly from such a method (Langenfeld, Moch, and Uwer, 2009). By the end of the Tevatron running, the experiments expect to increase the data set by at least a factor of 4 compared to the published results and at least a factor of 2 for the data sets used in the combination. Thus, the statistical precision can be improved, but the systematic uncertainties will also need to be improved if the full statistical power of the final data set is to be realized. in which c  cosà is the cosine of the decay angle in the W rest frame measured with respect to the top-quark direction. Both CDF (Aaltonen et al., 2009i) and D0 (Abazov et al., 2008g) measured the helicity fractions in top-quark decay. R The CDF analysis uses Ldt ¼ 1:9 fbÀ1 , and the D0 result R is based on Ldt ¼ 1:0 fbÀ1 . Both experiments select events in the ‘ þ jets topology, and D0 also uses the ‘‘ þ X topology. The initial selections are similar to those described earlier in Sec. IV.A. CDF uses a second selection with somewhat different requirements to perform an independent analysis. The CDF results are from the combination of the two methods. All results rely on reconstructing the cosà distribution and comparing that to a set of predicted dis...
View Full Document

This document was uploaded on 09/28/2013.

Ask a homework question - tutors are online