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Angular correlations in t-channel single top production at the LHC

Patrick Motylinski

TL;DR

This work investigates the angular correlation between the top quark spin and the decay lepton in t-channel single-top production at the LHC using MC@NLO. It analyzes two spin-quantization bases—spectator and beamline—and demonstrates that both produce highly polarized top samples, with the spectator basis favored for top and the beamline basis (with a rapidity cut) favorable for anti-top. The study shows that the correlations are robust against PDFs, factorization scale, center-of-mass energy, and jet radius, with polarization and asymmetry variations typically within a few percent. These findings support the feasibility of measuring angular correlations at the LHC to probe the V−A structure of the Wtb vertex and the underlying top-quark couplings, using NLO-accurate event generation and parton-shower matching.

Abstract

When a top quark decays there is a large amount of angular correlation, in its rest frame, between its spin orientation and the direction of flight of the charged lepton from its decay. In this letter we investigate the prospects of measuring this angular correlation using the MC@NLO framework. The strength of the correlation is investigated for different spin bases. The robustness against variations of PDF sets and uncertainties, factorization scale dependence, center-of-mass energy, and the jet R-parameter, is also examined.

Angular correlations in t-channel single top production at the LHC

TL;DR

This work investigates the angular correlation between the top quark spin and the decay lepton in t-channel single-top production at the LHC using MC@NLO. It analyzes two spin-quantization bases—spectator and beamline—and demonstrates that both produce highly polarized top samples, with the spectator basis favored for top and the beamline basis (with a rapidity cut) favorable for anti-top. The study shows that the correlations are robust against PDFs, factorization scale, center-of-mass energy, and jet radius, with polarization and asymmetry variations typically within a few percent. These findings support the feasibility of measuring angular correlations at the LHC to probe the V−A structure of the Wtb vertex and the underlying top-quark couplings, using NLO-accurate event generation and parton-shower matching.

Abstract

When a top quark decays there is a large amount of angular correlation, in its rest frame, between its spin orientation and the direction of flight of the charged lepton from its decay. In this letter we investigate the prospects of measuring this angular correlation using the MC@NLO framework. The strength of the correlation is investigated for different spin bases. The robustness against variations of PDF sets and uncertainties, factorization scale dependence, center-of-mass energy, and the jet R-parameter, is also examined.

Paper Structure

This paper contains 6 sections, 4 equations, 8 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Angular Correlations in the $t$-channel
  3. Spectator Basis
  4. Beamline Basis
  5. Numerical Results
  6. Conclusions

Figures (8)

  • Figure 1: Single top $t$-channel diagram.
  • Figure 2: Pseudorapidity of the hardest (non-$b$) jet for single top (left) and single anti-top production (right).
  • Figure 3: Angular correlation in single top (left) and single anti-top (right) production.
  • Figure 4: Angular correlation in single top (left) and single anti-top (right) production when cuts are applied (see text).
  • Figure 5: Angular correlation in single-$t$ production using three different PDF sets. The left plot is made using the spectator basis while the right plot using the beamline basis with $|\eta_{j_1}|>$2.5.
  • ...and 3 more figures