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

Of integrated luminosity has been acquired the higher

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: words, hadron collisions at Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1488 the Tevatron and LHC sample events with a larger pffiffiffi ^ average s as comparedffiffiffito LEP collision energies and p ^ it is exactly those high s events that are most sensitive to effects of anomalous couplings from new physics at higher-energy scale. "  Because the Tevatron is a pp collider, the production cross sections for W þ Z and W À Z are equal. The same is true for W þ and W À production. When produced in a pp collider such as the LHC, positive and negative net charge diboson states have different production cross sections [e.g., ðpp ! W þ ZÞ > ðpp ! W À ZÞ]. 2. W The W final state observed at hadron colliders provides a direct test of the WW TGC. Anomalous WW couplings lead to an enhancement in the production cross section and an excess of large ET photons. Both CDF and D0 published measurements of the W cross section using leptonic decays R of the W bosons and Ldt ¼ 0:2 fbÀ1 (Abazov et al., 2005a; Acosta et al., 2005a). The signature of the W signal is an isolated high ET lepton, an isolated high ET photon, and large ET due to the neutrino from the W decay. The dominant 6 background is from W þ jets where a jet mimics an isolated photon. A lepton-photon separation requirement in  À  pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi space of ÁR ¼ ðÁÞ2 þ ðÁÞ2 > 0:7 is made by both CDF and D0 to suppress events with final-state radiation of the photon from the outgoing lepton and to avoid collinear singularities in theoretical calculations. A kinematic requirement on photon ET of ET > 7 (8) GeV is made by CDF (D0) in the analysis. CDF measures " ðpp ! W þ X Þ Â BRðW ! lÞ ¼ 18:1 Æ 1:6ðstatÞ Æ 2:4ðsystÞ Æ 1:2ðlumÞ pb (Acosta et al., 2005b) in agreement with the next-to-leadingorder (NLO) theoretical expectation (ET > 7 GeV) (Baur and Berger, 1993) of 19:3 Æ 1:4 pb. D0 measures " ðpp ! W þ X Þ Â BRðW ! lÞ ¼ 14:8 Æ 1:6ðstatÞ Æ 1:0ðsystÞ Æ 1:0ðlumÞ pb (Abazov et al., 2005a) also in agreement with the NLO expectation (ET > 8 GeV) (Baur and Berger, 1993) of 16:0 Æ 0:4 pb. Table VI summarizes the W cross-section measurement results. Both CDF and D0 W cross-section measurement are consistent with the SM expectations at NLO. In a more recent analysis (Abazov et al., 2008b), D0 uses 4 times more integrated luminosity as compared to Abazov et al. (2005a) and adds photons reconstructed in their end cap calorimeters (1:5 < jdet j < 2:5) to search for anomalous WW couplings based on the observed photon ET spectrum (Abazov et al., 2008b) for photons with ET > 9 GeV. Additionally, the three-body transverse mass of the photon, lepton, and ET must exceed 120 GeV=c (110 GeV=c) for the 6 electron (muon) channel in order to suppress final-state radiation. The photon ET spectrum and...
View Full Document

This document was uploaded on 09/28/2013.

Ask a homework question - tutors are online