[Paper Review] Soft gluon resummation for squark and gluino pair-production at hadron colliders

W. Beenakker, Silja Brensing+5 more|arXiv (Cornell University)|Jan 18, 2010

Particle physics theoretical and experimental studies1 references4 citations

TL;DR

This paper presents next-to-leading-logarithmic (NLL) soft gluon resummation for squark and gluino pair-production at hadron colliders, using one-loop anomalous dimensions to resum threshold logarithms. The method improves theoretical cross-section predictions by up to 18% at the Tevatron and reduces theoretical uncertainties by ~30%, with results applicable to LHC and Tevatron searches for supersymmetry beyond NLO accuracy.

ABSTRACT

We report on the study of soft gluon effects in the production of squarks and gluinos at hadron colliders. Close to production threshold, the emission of soft gluon results in the appearence of large logarithmic corrections in the theoretical expressions. In order to resum these corrections at next-to-leading-logarithmic accuracy appropriate one-loop anomalous dimensions have to be calculated. We present the calculation of the anomalous dimensions for all production channels of squarks and gluinos and provide numerical predictions for the Tevatron and the LHC.

Motivation & Objective

• To improve theoretical predictions for squark and gluino pair-production at hadron colliders by resumming large threshold logarithms from soft gluon emission.
• To calculate one-loop anomalous dimensions for all relevant production channels involving squarks and gluinos.
• To provide accurate, resummed cross-section predictions for the Tevatron and LHC, enhancing precision for SUSY searches.
• To reduce theoretical uncertainties in sparticle production cross sections through NLL resummation matched with NLO results.
• To enable more reliable exclusion limits and sparticle mass determinations in experimental SUSY searches at hadron colliders.

Proposed method

• Uses Mellin moment space to resum threshold logarithms of the form αs^n log^k(β²) with k=2n,…,0, where β=√(1−4m²/ŝ).
• Applies a color-singlet basis in SU(3) color space to diagonalize soft anomalous dimension matrices, simplifying resummation.
• Calculates one-loop soft anomalous dimensions D_ij→kl,I^(1) for all production channels (qq̄→q̄q̄, qg→q̄g, etc.) in irreducible SU(3) representations.
• Matches NLL-resummed cross sections with complete NLO results via the NLL+NLO scheme to ensure accuracy across all energy scales.
• Employs MSTW 2008 NLO parton distribution functions and two-loop αs in the MS̄ scheme with five active flavors.
• Performs scale variation (m/2 ≤ μ ≤ 2m) to estimate theoretical uncertainties in the final cross-section predictions.

Experimental results

Research questions

• RQ1 How do soft gluon corrections affect the total cross sections for squark and gluino pair-production at hadron colliders near threshold?
• RQ2 What is the impact of NLL soft gluon resummation on theoretical uncertainties in sparticle production cross sections?
• RQ3 How do the resummed cross sections compare to NLO results across different sparticle mass scales and collider energies?
• RQ4 Which production channels (e.g., gg→gg̃, qg→q̃g̃) exhibit the largest corrections due to soft gluon emission?
• RQ5 To what extent does soft gluon resummation improve the accuracy of SUSY cross-section predictions for the Tevatron and LHC?

Key findings

• NLL soft gluon resummation increases the total cross section by up to 18% for inclusive squark and gluino production at the Tevatron when the average sparticle mass is 600 GeV.
• The NLL+NLO cross sections reduce theoretical uncertainties by approximately 30% compared to NLO alone, due to scale variation in the range m/2 ≤ μ ≤ 2m.
• The largest corrections arise in processes with gluon initial states and gluinos in the final state, due to high color charge and Casimir invariants.
• At the LHC, corrections are smaller than at the Tevatron for sparticle masses below 3 TeV, due to a larger average distance from threshold (1−ρ).
• The resummed results for inclusive production (pp̄→q̄q̄+q̄q̄+q̄g̃+g̃g̃+X) represent the most accurate theoretical predictions currently available for these processes.
• The soft anomalous dimension coefficients D_ij→kl,I^(1) are explicitly calculated for all channels, with values such as {−4/3, −10/3} for q̄q→q̄q̄ and {−4/3, −10/3, −16/3} for qg→q̄g̃ in different SU(3) irreducible representations.