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

Manifest themselves the third is to do experiments at

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Unformatted text preview: hird is to do experiments at such high energy E that the effects of these operators, of order ðE=ÃÞ2 , become large. If E > Ã, then one must abandon this formalism, because operators of arbitrarily high dimensionality become significant; however, the new physics should then be directly observable. If no effects beyond the SM are observed, then one can place bounds on the coefficients of the dimension-six operators c=Ã2 , where c is a dimensionless number. These bounds apply only to the product c=Ã2 , not to c and Ã2 separately; in fact, there could even be two different scales of new physics involved (Ã1 Ã2 in place of Ã2 ). This approach to physics beyond the SM, dubbed an effective-field-theory approach (Weinberg, 1979), has the advantage of being model independent. Whatever new physics lies at the scale Ã, it will induce dimension-six operators, whose only dependence on the new physics lies in their coefficients, c=Ã2 . Another advantage of this approach is that it is universal; it can be applied to both tree-level and loop-level processes, and any ultraviolet divergences that appear in loop processes can be absorbed into the coefficients of the operators. Thus, one need not make any ad hoc assumptions about how the ultraviolet divergences are cut off. This effective-field-theory approach thus provides an excellent framework to parametrize physics beyond the SM (De Rujula et al., 1992; Hagiwara et al., 1993). Hadron colliders contribute to the study of the electroweak interactions in three distinct ways. First, because they operate at the energy frontier, hadron colliders are uniquely suited to searching for the effects of dimension-six operators that are Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . suppressed by a factor of ðE=ÃÞ2 . Second, they are able to contribute to the precision measurement of a variety of electroweak processes, most notably to the measurement of the W boson mass and the top-quark mass. Third, they are able to search for new particles associated with the electroweak interactions, in particular, the Higgs boson. These three virtues of hadron colliders will manifest themselves throughout this review. A. Electroweak interactions The electroweak theory is a spontaneously broken gauge theory based on the gauge group SUð2ÞL  Uð1ÞY . There are three parameters that describe the theory: the gauge couplings g and g0 , and the order parameter of spontaneous symmetry breaking v. In the SM, this order parameter is the vacuumexpectation value of a fundamental Higgs field. These parameters are not measured directly, but rather inferred from precision electroweak measurements. The three measurements that are used to fix these parameters are the Fermi constant GF determined from the muon lifetime formula; the fine-structure constant , determined from a variety of lowenergy experiments; and the Z boson mass MZ . With these three inputs, the predictions of all other ele...
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This document was uploaded on 09/28/2013.

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