Search for (W/Z {u2192} Jets) + ? Events in Proton-Antiproton Collisions at the Fermilab Tevatron

Book excerpt: We present a study of the p¯p → W(Z)? → ?q¯q process at the center-of-mass energy √s = 1.96 TeV using data collected by the Collider Detector at Fermilab. The analysis is based on the selection of low transverse momentum photons produced in association with at least two jets. A modification of an existing photon trigger was studied and implemented in the data acquisition system to enhance the sensitivity of this analysis. The data presented are from approximately 184 pb-1 of integrated luminosity collected by this new trigger. A preliminary event sample is obtained requiring a central photon with ET > 12 GeV and two jets with ET > 15 GeV. The corresponding efficiency is studied using a Monte Carlo simulation of the W(Z)? → ?q¯q based on Standard Model predictions. Monte Carlo estimation of the background is not necessary as it is measured from the data. A more advanced selection based on a Neural Network method improves the signal-to-noise ratio from 1/333 to 1/71, and further optimization of the dijet mass search region increases the ratio to its final value of 1/41. No evidence of a W/Z → q¯q peak in the dijet mass distribution is visible when the background contribution is subtracted. Using a fully Bayesian approach, the 95% confidence level upper limit on ?(p¯p → W?) x ?(W → q¯q) + ?(p¯p → Z?) x ?(Z → q¯q) is calculated to be 54 pb, which is consistent with the Standard Model prediction of 20.5 pb.