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

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

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Unformatted text preview: tributions each of which is generated with a different pair of f0 and fþ values. Several ambiguities arise in reconstructing cosà . These include the assignment of the reconstructed jets to the quarks from W decay (for the hadronic side of ‘ þ jets events) and the impact from the unmeasured  value for the neutrino Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1509 " TABLE XXIV. W boson helicity fractions in tt decay determined from fits to data. The first two lines are the results from simultaneous fits for f0 and fþ . The third line is the result from the fit for f0 with fþ ¼ 0, and the fourth is from the fit for fþ with f0 set to the SM value. In all cases, the statistical uncertainty is shown first and the second uncertainty is the systematic uncertainty. CDF f0 fþ f 0 , fþ ¼ 0 fþ , f0 ¼ 0:70 D0 0:66 Æ 0:16 Æ 0:05 À0:03 Æ 0:06 Æ 0:03 0:62 Æ 0:10 Æ 0:05 À0:03 Æ 0:04 Æ 0:03 0:425 Æ 0:166 Æ 0:102 0:119 Æ 0:090 Æ 0:053 0:619 Æ 0:090 Æ 0:052 À0:002 Æ 0:047 Æ 0:047 arising in leptonic W decay. These issues are handled differently in the three (two CDF, one D0) analyses. The CDF analyses use only the leptonic W decay. The D0 analysis also uses the jets from the hadronic W , but only j cosà j is reconstructed for these, not cosà . Although this loses the ability to distinguish fþ from fÀ for the hadronic decay, f0 is better constrained. The results are extracted using likelihood fits to test cosà distributions. For one of the CDF methods and the D0 analysis, predicted reconstructed cosà distributions including signal and background contributions are generated using simulated events. The distributions are generated for a range of f0 and fþ values, and best values are extracted using likelihood comparisons to the data. For the second CDF method, the result is compared to a distribution generated by convoluting the true cosà distribution divided into six bins with a migration function which gives the probability that an event generated in a given true bin ends up as a given reconstructed bin. This function includes the effects of resolution and acceptance. Effects of helicity on the acceptance are considered in all cases. The experimental results are summarized in Table XXIV. The results are consistent with each other and with the SM prediction. They are generally limited by the statistical precision of the data set and are expected to improve by a factor between Â2 and Â10 by the end of Run II, depending on the analysis and machine performance achieved. Even if there is no improvement in the systematic uncertainty, the final results will still be statistics limited, but the statistical and systematic uncertainties will be similar. The dominant sys" tematic uncertainty in the D0 result comes from the tt production and decay model which was tested by comparing results from events generated using the PYTHIA generator (Sjostrand et al., 2001) and with the default...
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This document was uploaded on 09/28/2013.

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