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

A next to next to leading order nnlo prediction

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Unformatted text preview: nd Z cross sections Using a next-to-next-to-leading order (NNLO) prediction (Hamberg, van Neerven, and Matsuura, 1991) calculated with the MRST2004 NNLO parton distribution function (Martin et al., 2004) and the SM branching fractions for the W and Z bosons into fully leptonic final states, the cross section times branching fractions are calculated to be " ðpp ! W Þ Â BðW ! ‘Þ ¼ 2687 Æ 54 pb and þ5: " ðpp ! ZÞ Â BðZ ! ‘‘Þ ¼ 251:9À110:8 pb: The uncertainties are a combination of the MRST2004 uncertainties and the difference between the central value above and that computed using the CTEQ6.1M parton distribution functions (Pumplin et al., 2002). The W and Z cross sections times branching fractions to fully leptonic final states have beenR measured by the CDF (Abulencia et al., 2007a) using Ldt ¼ 72 pbÀ1 . The results for electron and muon channels combined are " ðpp ! W Þ Â BðW ! ‘Þ ¼ 2749 Æ 10ðstatÞ Æ 53ðsystÞ Æ 165ðlumiÞ pb and " ðpp ! ZÞ Â BðZ ! ‘‘Þ ¼ 254:9 Æ 3:3ðstatÞ Æ 4:6ðsystÞ Æ 15:2ðlumiÞ pb: The measurements of the Z cross section include additional contributions from à and Z= à interference which gives events that are experimentally indistinguishable from the Z process. The size of these contributions depends on the Z= à mass range considered. For the range 60 MðZ= Ã Þ < 130 GeV=c2 , these contributions increase the cross section by a factor of 1:019 Æ 0:001 relative to the Z-only cross section, and for the mass range 66 MðZ= ÃÞ < 116 GeV=c2 , the cross section is increased by a factor of 1:004 Æ 0:001. A precision measurement of the ratio R of W and Z cross section times branching fraction given by Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1481 TABLE I. The measured integrated luminosity, yield, background, signal acceptance times efficiency, and resulting   Br for each of the four Z cross-section times branching ratio analyses by the CDF Collaboration in Abulencia et al. (2007a). The combination of the dielectron and dimuon channels using the BLUE method is also shown. The Z= à results have been corrected to Z only as described in the text. Channel Integrated luminosity 72 pb 72 pb W ! e W !  À1 À1 Predicted background AÂ Measured   Br 37 584 1762 Æ 300 þ0 062 2:771 Æ 0:014À0::056 Æ 0:166 nb 31 722 3469 Æ 151 þ0 0034 0:1795À0::0038 þ0 0031 0:1442À0::0034 Data yield þ0 066 2:722 Æ 0:015À0::061 Æ 0:163 nb ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ 2:749 Æ 0:010 Æ 0:053 Æ 0:165 nb Z ! ee 72 pbÀ1 4 242 62 Æ 18 þ0 0047 0:2269À0::0048 255:8 Æ 3:9þ5::5 Æ 15:3 pb À5 4 Z !  ee and  72 pbÀ1 ÁÁÁ 1 785 ÁÁÁ 13 Æ 13 ÁÁÁ þ0 0028 0:0992À0::0031 ÁÁÁ 248:0 Æ 5:9þ8::0 Æ 14:8 pb À7 2 254:9 Æ 3:3 Æ 4:6 Æ 15:2 pb e and  R¼ " ðpp ! W Þ Â BðW ! ‘Þ " ðpp ! ZÞ Â BðZ ! ‘‘Þ can be used to test the SM. For example, new high mass resonances...
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This document was uploaded on 09/28/2013.

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