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

The sensitive range is limited to mh 250 gevc2 6

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Unformatted text preview: Â BðW ! ‘Þ ðpp ! ZHÞ  Â BðZ ! ‘‘Þ  Â BðZ ! Þ 100 110 120 130 286 209 153 115 63.6 46.4 34.0 25.5 where there exists sufficient center-of-mass collision energy at the parton level for an appreciable rate of Higgs-boson production via the gluon fusion (ggH ) process which proceeds via a virtual quark loop (dominated by the top quark) (Djouadi, 2008). For mH & 135 GeV=c2 (the ‘‘low mass Higgs’’ region), the dominant Higgs decay is to b-quark pairs. The next largest contribution to the Higgs decay in the low mass Higgs region is H !  which has a branching ratio of $7%. In the case of H ! bb, the ggH production is not useful to the direct Higgs search even using the bb invariant mass because of overwhelming continuum bb production. Instead, the associated vector boson (VH ) process where the Higgs boson is produced in association with a W or Z boson is used. The additional leptons which can result from decay of the vector boson via W ! ‘, Z ! ‘‘, or Z !  with ‘ ¼ e,  (Stange, Marciano, and Willenbrock, 1994a, 1994b), whether detected directly or indirectly through ET , 6 can be used to suppress backgrounds at the expense of a lower cross section for VH as compared to ggH . The cross section and cross section times branching fraction for several Higgs masses in the low mass Higgs region (Tevatron New Phenomena and Higgs Working Group, 2009) are shown in Table XXVIII. In addition to the modes listed in 0 0 Table XXVIII, the WH ! WWW ! ‘Æ ‘þ ‘À channel provides some sensitivity in the transition region around mH % 135 GeV=c2 and vector boson fusion (VBF) qq ! qqH and ggH modes provide sensitivity in  final states. " For the low mass associated production channels VH in which the W or Z boson decay involves one or two charged lepton(s), an initial sample consistent with production of a vector boson decaying to charged and/or neutral leptons and having at least two jets is selected. This sample has a very low signal-to-noise ratio but is already dominated by vector boson events and therefore provides a control sample used to validate detector modeling and rate predictions of the dominant backgrounds in the final analysis. The requirement that one or more of the jets in the event is consistent with production of a B hadron is added to the selection, dramatically reducing the contribution from the initially dominant Vjj background and increasing the signal purity. Nonlinear multivariate techniques for each final state are used to combine kinematic properties into a (typically) single variable in which a potential Higgs signal and backgrounds populate different regions. The distributions of these variables are then used as input to binned likelihood fits in which signal and background fractions are allowed to float within constraints of the total yield, predicted background contributions, and all uncertainties. The absence (presence) Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 167 124 92...
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