TY  - JOUR
AU  - Aguilar-Saavedra, J. A.
AU  - Bernabeu, J.
PY  - 2010
DA  - 2010//
TI  - W polarisation beyond helicity fractions in top quark decays
T2  - Nucl. Phys. B
JO  - Nuclear Physics B
SP  - 349
EP  - 378
VL  - 840
IS  - 1-2
PB  - Elsevier Science Bv
AB  - We calculate the density matrix for the decay of a polarised top quark into a polarised W boson and a massive 17 quark, for the most general Wth 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 defining and studying the transverse and normal W polarisation fractions, that is, the W polarisation alone 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 Wth 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 Wth vertex. Finally we show that, using a combined fit to top decay observables and the t W cross section, at LHC it will be possible to obtain model-independent measurements of all the (complex) Wth couplings as well as the single top polarisation. Implications for spin correlations in top pair production are also discussed.
SN  - 0550-3213
UR  - http://arxiv.org/abs/1005.5382
UR  - https://doi.org/10.1016/j.nuclphysb.2010.07.012
DO  - 10.1016/j.nuclphysb.2010.07.012
LA  - English
N1  - ISI:000281832900013
ID  - Aguilar-Saavedra+Bernabeu2010
ER  -