W polarisation beyond helicity fractions in top quark decays

被引：74

作者：

Aguilar-Saavedra, J. A. ^{[1
,2
]}

Bernabeu, J. ^{[3
,4
,5
]}

机构：

[1] Univ Granada, Dept Fis Teor & Cosmos, E-18071 Granada, Spain

[2] Univ Granada, CAFPE, E-18071 Granada, Spain

[3] Univ Valencia, CSIC, Dept Fis Teor, E-46100 Burjassot, Valencia, Spain

[4] Univ Valencia, CSIC, IFIC, E-46100 Burjassot, Valencia, Spain

[5] CERN, Div Theory, CH-1211 Geneva 23, Switzerland

来源：

NUCLEAR PHYSICS B | 2010年 / 840卷 / 1-2期

关键词：

ATLAS SENSITIVITY; TAU-POLARIZATION; PAIR PRODUCTION; CP VIOLATION; COUPLINGS; PHYSICS; MODEL; MOMENT; BOSON; LHC;

D O I：

10.1016/j.nuclphysb.2010.07.012

中图分类号：

O412 [相对论、场论]; O572.2 [粒子物理学];

学科分类号：

摘要：

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. (C) 2010 Elsevier B.V. All rights reserved.

引用

页码：349 / 378

页数：30

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