[Paper Review] Higher-order Threshold Corrections for Single Top Quark Production

Nikolaos Kidonakis|arXiv (Cornell University)|Jan 1, 2007

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper computes higher-order soft-gluon threshold corrections for single top quark production at the Tevatron and LHC, using threshold resummation to NNNLO accuracy. It finds significant enhancements—up to 65% at the Tevatron (s-channel) and 55% at the LHC (s-channel)—demonstrating that soft-gluon effects dominate near threshold and improve cross-section predictions beyond leading order.

ABSTRACT

I discuss single top quark production at the Tevatron and the LHC. The cross section, including soft-gluon threshold corrections through NNNLO, is presented for each partonic channel. The higher-order corrections provide significant contributions to the single top cross sections at both colliders.

Motivation & Objective

• To compute higher-order soft-gluon corrections for single top quark production at hadron colliders.
• To assess the impact of threshold resummation through NNNLO in αs for t, s, and tW channels.
• To provide improved cross-section predictions by matching soft-gluon corrections to exact NLO results.
• To quantify scale and PDF uncertainties in the context of threshold-enhanced QCD corrections.

Proposed method

• Uses threshold resummation to compute soft-gluon corrections through NNNLO in αs at NLL accuracy.
• Applies eikonal approximation for one-loop calculations to derive coefficients in the logarithmic expansion.
• Derives expressions for d2σ/dt du with terms in ln^l(s4/m_t^2)/s4+, δ(s4), and scale-dependent terms (μR, μF).
• Incorporates β0 = (11CA - 2nf)/3 for the running coupling and uses CF = (Nc² - 1)/(2Nc), CA = Nc with Nc = 3.
• Matches soft-gluon corrections to exact NLO cross sections to improve accuracy.
• Employs MRST 2004 NNLO parton distribution functions for numerical results.

Experimental results

Research questions

• RQ1 How do soft-gluon corrections affect single top quark cross sections at the Tevatron and LHC?
• RQ2 To what extent do NNNLO threshold corrections enhance the cross section in different partonic channels?
• RQ3 How do the K-factors (higher-order/LO ratios) vary across t, s, and tW channels at both colliders?
• RQ4 How do scale and PDF uncertainties affect the final cross-section predictions?
• RQ5 In which channels is the threshold approximation valid compared to full QCD corrections?

Key findings

• At the Tevatron, s-channel single top production sees up to 65% enhancement from NNNLO corrections, yielding σ = 0.56 ± 0.03 pb at mt = 170 GeV.
• For the t channel at the Tevatron, corrections are smaller (up to ~15% enhancement), with σ = 1.17 ± 0.06 pb at mt = 170 GeV.
• At the LHC, s-channel single top production receives up to 55% enhancement, resulting in σ_top = 8.0+0.6/-0.5 pb at mt = 170 GeV.
• The tW channel at the LHC shows ~60% enhancement, with σ = 44 ± 5 pb at mt = 170 GeV, making it a dominant channel.
• For the t channel at the LHC, soft-gluon corrections are less reliable; only exact NLO results are updated, yielding σ_top = 152 ± 6 pb at mt = 170 GeV.
• The paper confirms that single antitop production cross sections are identical to top production in t and s channels, but differ in tW channel due to charge conjugation symmetry.