Evidence for production of single top quarks
Contribuinte(s) |
Universidade Estadual Paulista (UNESP) |
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Data(s) |
30/09/2013
20/05/2014
30/09/2013
20/05/2014
01/07/2008
|
Resumo |
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron p (p) over bar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a 0.9 fb(-1) data set that have an electron or muon and missing transverse energy from the decay of a W boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W + jets and t (t) over bar events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of sigma(p (p) over bar -> tb + X, tqb + X) = 4.7 +/- 1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the Wtb coupling and find vertical bar V(tb)f(1)(L)vertical bar = 1.31(-0.21)(+0.25), where f(1)(L) is a generic vector coupling. This model-independent measurement translates into 0.68 <vertical bar V-tb vertical bar <= 1 at the 95% C.L. in the standard model. |
Formato |
47 |
Identificador |
http://dx.doi.org/10.1103/PhysRevD.78.012005 Physical Review D. College Pk: Amer Physical Soc, v. 78, n. 1, p. 47, 2008. 1550-7998 http://hdl.handle.net/11449/24395 10.1103/PhysRevD.78.012005 WOS:000258636400018 WOS000258636400018.pdf |
Idioma(s) |
eng |
Publicador |
Amer Physical Soc |
Relação |
Physical Review D |
Direitos |
closedAccess |
Tipo |
info:eu-repo/semantics/article |