Search for Single Top Quark Production at DØ Using Neural Networks
نویسندگان
چکیده
We present a search for electroweak production of single top quarks in ≈90 pb −1 of data collected with the DØ detector at the Fermilab Tevatron collider. Using arrays of neural networks to separate signals from backgrounds, we set upper limits on the cross sections of 17 pb for the s-channel process p¯ p → tb + X, and 22 pb for the t-channel process p¯ p → tqb + X, both at the 95% confidence level. 4 According to the standard model, top quarks can be produced at the Tevatron p¯ p collider via two mechanisms. One involves a virtual gluon that decays via the strong interaction into a t ¯ t pair. This mode has been observed by the CDF and DØ collaborations [1,2]. The second mechanism involves the electroweak production of a single top quark at a W tb vertex, where W and b refer to the W boson and b quark. There are three ways of producing a single top quark: an s-channel process q ¯ q→t ¯ b, a t-channel mode q g→tq ¯ b, and a final state generated via both the sand t-channels, bg→tW. For a top quark of mass 174.3 ± 5.1 GeV [3], the predicted cross sections are 0.75 ± 0.12 pb for tb production [4] and 1.47 ± 0.22 pb for tqb production [5], both calculated at next-to-leading-order precision with √ s = 1.8 TeV. For tW production, the cross section is 0.15 pb at leading order [6]. The errors on the cross sections include contributions from the choice of parton distribution functions (PDF), the uncertainty on the gluon distribution, the choice of scale, and the experimental error on the top-quark mass measurement. In this Letter, we use the notation " tb " to refer to both t ¯ b and the charge-conjugate process ¯ tb, and " tqb " to refer to both tq ¯ b and ¯ t¯ qb. The DØ collaboration recently published its first results on the production of single top quarks [7]. The search used a classical selection method to optimize the signal significance, based on the expected kinematic properties of the events. The 95% confidence level upper limits on the cross sections were determined to be 39 pb for the s-channel process and 58 pb for the t-channel process. The events contained an isolated electron or muon [8], missing transverse energy, and jets. At …
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تاریخ انتشار 2001