W polarisation beyond helicity fractions in top quark decays

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.

LaTeX 36 pages, 51 EPS figures. Typos corrected. To appear in NPB

References in corpus (15)

• A minimal set of top-Higgs anomalous couplings
• Single top quark production at LHC with anomalous Wtb couplings
• The Hunt for New Physics at the Large Hadron Collider
• Probing anomalous Wtb couplings in top pair decays
• Search for New Physics via Single Top Production at the LHC
• Top production at the Tevatron/LHC and nonstandard, strongly interacting spin one particles
• Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization
• Tau anomalous magnetic moment form factor at Super B/Flavor factories
• ATLAS sensitivity to Wtb anomalous couplings in top quark decays
• CP violating anomalous top-quark couplings at the LHC
• T-odd correlations from CP violating anomalous top-quark couplings revisited
• The Top Quark Decay Vertex in Standard Model Extensions
• Zt, gamma t and t production at hadron colliders via strong flavour-changing neutral couplings
• CP violation and electric-dipole-moment at low energy $\tau$ production with polarized electrons
• CP-odd correlations using jet momenta from tt_bar events at the Tevatron

Cited by in corpus (68)

• The Standard Model as an Effective Field Theory
• Physics at the e+ e- Linear Collider
• Non-resonant New Physics in Top Pair Production at Hadron Colliders
• Constraining top quark effective theory in the LHC Run II era
• Effective four-fermion operators in top physics: a roadmap
• Measurement of the W boson polarization in top quark decays with the ATLAS detector
• A global fit of top quark effective theory to data
• Pinning down electroweak dipole operators of the top quark
• Measurement of top quark pair production in association with a Z boson in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Global and optimal probes for the top-quark effective field theory at future lepton colliders
• Single-top-quark production in the $t$-channel at NNLO
• A General Analysis of Wtb anomalous Couplings
• Breaking down the entire W boson spin observables from its decay
• Measurement of the W boson helicity fractions in the decays of top quark pairs to lepton + jets final states produced in pp collisions at sqrt(s) = 8 TeV
• Top Quark Physics at the LHC: A Review of the First Two Years
• Measurement of the W-boson helicity in top-quark decays from ttbar production in lepton+jets events in pp collisions at sqrt(s) = 7 TeV
• Top polarisation studies in $H^{-}t$ and $Wt$ production
• Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at sqrt(s) = 8 TeV
• Bottom-Flavored Mono-Tau Tails at the LHC
• Top effective operators at the ILC
• Measurement of top quark polarisation in t-channel single top quark production
• Probing anomalous tbW couplings in single-top production using top polarization at the Large Hadron Collider
• New directions for top quark polarization in the $t$-channel process
• Constraints on the Wtb vertex from early LHC data
• Search for anomalous couplings in the $Wtb$ vertex from the measurement of double differential angular decay rates of single top quarks produced in the $t$-channel with the ATLAS detector
• Single top-quark production at the Tevatron and the LHC
• Probing $tt\gamma$ and $ttZ$ couplings at the LHeC
• Studying the $Wtb$ vertex structure using recent LHC results
• Top-Quark Physics: Status and Prospects
• Probing the $Wtb$ vertex structure in $t$-channel single-top-quark production and decay in $pp$ collisions at $\sqrt{\mathrm{s}}=8$ TeV with the ATLAS detector
• New limits on anomalous contributions to the $Wtb$ vertex
• Single top quark production at the LHC
• Measurement of differential cross sections and charge ratios for $t$-channel single top quark production in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Top quark tensor couplings
• Model-independent measurement of the top quark polarisation
• Probing anomalous $Wtb$ couplings at the LHC in single top quark production through $t$-channel
• Off-shell single-top-quark production in the Standard Model Effective Field Theory
• Effective operators in $t$-channel single top production and decay
• Analysis of the $Wtb$ vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the $t$-channel at $\sqrt{s}$ = 8 TeV with the ATLAS detector
• Top quark anomalous tensor couplings in the two-Higgs-doublet models
• Top couplings and top partners
• Inclusive and differential cross section measurements of single top quark production in association with a Z boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Effective Field Theory in the top sector: do multijets help?
• Full analysis of general non-standard tbW couplings
• Using single top rapidity to measure V_td, V_ts, V_tb at hadron colliders
• Global Constraints on Top Quark Anomalous Couplings
• A survey of top quark polarization at a polarized linear e^+ e^- collider
• The fully differential top decay distribution
• Limits on the anomalous $Wtq$ couplings
• Top and bottom tensor couplings from a color octet scalar
• The top quark right coupling in the tbW-vertex
• Jets with electrons from boosted top quarks
• Dilepton azimuthal correlations in $t\bar{t}$ production
• New physics with boosted single top production at the LHC and future colliders
• Anomalous top charged-current contact interactions in single top production at the LHC
• Top Couplings: pre-Snowmass Energy Frontier 2013 Overview
• W boson polarization as a measure of gauge-Higgs anomalous couplings at the LHC
• Polarization of a vector boson produced in decay of a heavy fermion in an arbitrary frame
• The right top coupling in the aligned two-Higgs-doublet model
• Top Quark Anomalous Couplings at the High-Luminosity Phase of the LHC
• Top quark physics in the Large Hadron Collider era
• Polarization in (quasi-)two-body decays and new physics
• Parametrizations of the Spin Density Matrix
• The Angular Correlations in Top Quark Decays in Standard Model Extensions
• Study of Top Effective Operators at the ILC
• Measurement of the inclusive and differential $\mathrm{t}\overline{\mathrm{t}}\gamma$ cross sections in the single-lepton channel and EFT interpretation at $\sqrt{s}$ = 13 TeV
• Top quark properties measurements at the LHC
• W-boson helicity fractions in top decay as probes of dimension-6 and dimension-8 SMEFT operators