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W polarisation beyond helicity fractions in top quark decays

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W polarisation beyond helicity fractions in top quark decays

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dc.contributor.author Aguilar Saavedra, Juan Antonio
dc.contributor.author Bernabeu Alberola, José
dc.date.accessioned 2016-05-04T07:52:25Z
dc.date.available 2016-05-04T07:52:25Z
dc.date.issued 2010
dc.identifier.citation Aguilar Saavedra, Juan Antonio; Bernabeu Alberola, José (2010) W polarisation beyond helicity fractions in top quark decays Nuclear Physics B 840 1-2 349 378
dc.identifier.uri http://hdl.handle.net/10550/53354
dc.description.abstract We calculate the density matrix for the decay of a polarised top quark into a polarised W boson and a massive b quark, for the most general Wtb vertex arising from dimension-six gauge-invariant effective operators. We show that, in addition to the well-known W helicity fractions, for polarised top decays it is worth to define and study the transverse and normal W polarisation fractions, that is, the W polarisation along two directions orthogonal to its momentum. In particular, a rather simple forward-backward asymmetry in the normal direction is found to be very sensitive to complex phases in one of the Wtb anomalous couplings. This asymmetry, which indicates a normal W polarisation, can be generated for example by a P-odd, T-odd transition electric dipole moment. We also investigate the angular distribution of decay products in the top quark rest frame, calculating the spin analysing powers for a general Wtb vertex. Finally we show that, using a combined fit to top decay observables and the tW cross section, at LHC it will be possible to obtain model-independent measurements of all the (complex) Wtb couplings as well as the single top polarisation. Implications for spin correlations in top pair production are also discussed.
dc.language.iso eng
dc.relation.ispartof Nuclear Physics B, 2010, vol. 840, num. 1-2, p. 349-378
dc.subject Física
dc.title W polarisation beyond helicity fractions in top quark decays
dc.type journal article es_ES
dc.date.updated 2016-05-04T07:52:25Z
dc.identifier.doi 10.1016/j.nuclphysb.2010.07.012
dc.identifier.idgrec 068989
dc.rights.accessRights open access es_ES

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