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Title

Measurement of W-boson helicity fractions in top-quark decays using cos theta

AuthorsCDF Collaboration; Cabrera, Susana CSIC ORCID; Cuenca Almenar, Cristóbal CSIC; Álvarez González, B.; Casal, Bruno CSIC; Cuevas, Javier CSIC ORCID; Gómez, G. CSIC ORCID ; Rodrigo, Teresa CSIC ORCID ; Ruiz Jimeno, Alberto ; Scodellaro, Luca CSIC ORCID ; Vila, Iván CSIC ORCID; Vilar, Rocío CSIC ORCID; Aaltonen, T.
KeywordsHelicity
W boson
Top quark
Issue Date20-Apr-2009
PublisherElsevier
CitationPhysics Letters - Section B 674 (3): 160-167 (2009)
AbstractFully reconstructed a t (t) over bar -> W(+)bW(-)(b) over bar -> l nu q (q) over bar 'b (b) over bar events are used to determine the fractions of right-handed (f(+)) and longitudinally polarized (f(0)) W bosons produced in top-quark decays. The helicity fractions are sensitive to the couplings and the Dirac structure of the Wtb vertex. This Letter reports measurements of the W-boson helicity fractions from two different methods using data corresponding to an integrated luminosity of 1.9 fb(-1) of pp collisions at a center-of-mass energy of 1.96 TeV collected by the CDF II detector operating at the Fermilab Tevatron. Combining the results from the two methods, we find f(0) = 0.62 +/- 0.10(stat) +/- 0.05(syst) under the assumption that f(+) = 0, and f(+) = -0.04 +/- 0.04(stat) +/- 0.03(syst) with f(0) fixed to the theoretically expected value of 0.70. Model-independent fits are also performed and simultaneously determine f(0) =0.66 +/- 0.16(stat) +/- 0.05(syst) and f(+) = -0.03 +/- 0.06(stat) +/- 0.03(syst). All these results are consistent with standard model expectations.
Publisher version (URL)http://dx.doi.org/ 10.1016/j.physletb.2009.02.040
URIhttp://hdl.handle.net/10261/22343
DOI10.1016/j.physletb.2009.02.040
ISSN0370-2693
Appears in Collections:(IFIC) Artículos

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