[Paper Review] Experimental Studies of Top Quark Production

J. Wagner-Kuhr|arXiv (Cornell University)|Jun 9, 2016

Particle physics theoretical and experimental studies187 references3 citations

TL;DR

This review synthesizes experimental studies of top quark production at the LHC and Tevatron, focusing on charge asymmetry in t\bar{t} production, resonant t\bar{t} searches, and t-channel single top quark production. It demonstrates that full NNLO QCD and electroweak NLO corrections resolve the Tevatron charge asymmetry puzzle, and that t-channel single top cross sections at 7 and 8 TeV agree with SM predictions within 9.5% uncertainty, confirming electroweak production with high precision.

ABSTRACT

In this review article three promising aspects of top quark production are discussed: the charge asymmetry in top quark pair production, the search for resonant top quark pair production, and electroweak single top quark production. First, an overview of the theoretical predictions of top quark pair and single top quark production is given. Then, for each topic the general analysis strategy and improvements are exemplarily explained using selected analyses and are put into the context of the global status at the beginning of LHC Run II and progress in this field. The example analyses discussed in more detail in this article use data from the LHC experiment CMS and for the charge asymmetry studies also data from the Tevatron experiment CDF have been used.

Motivation & Objective

• To review and synthesize experimental progress in top quark production studies at the LHC and Tevatron as of LHC Run II.
• To assess the significance of charge asymmetry in top quark pair production and resolve discrepancies between Tevatron measurements and SM predictions.
• To evaluate the sensitivity and results of searches for resonant top quark pair production using boosted topologies.
• To establish the precision of t-channel single top quark cross-section measurements and their role in testing electroweak couplings.
• To evaluate the potential of LHC Run II for improved measurements of top quark properties and new physics searches.

Proposed method

• Utilizes data from the CMS and CDF experiments at the LHC and Tevatron, respectively, for comparative analysis.
• Applies multivariate analysis techniques (e.g., BDTs) to enhance signal-background separation in t-channel and Wt single top production.
• Employs event reconstruction and kinematic fitting to identify top quark decays in the lepton+jets and dilepton final states.
• Performs cross-section measurements using integrated luminosities of up to 12.2 fb⁻¹ at √s = 8 TeV.
• Uses theoretical predictions at NNLO QCD and NLO electroweak levels to compare with experimental results.
• Sets upper limits on anomalous couplings (e.g., FCNC) in single top quark production using stringent statistical criteria.

Experimental results

Research questions

• RQ1 To what extent do full NNLO QCD and electroweak NLO corrections resolve the large charge asymmetry observed at the Tevatron?
• RQ2 What is the sensitivity of LHC Run I data to resonant top quark pair production, and how does it improve in Run II?
• RQ3 How precisely can the t-channel single top quark production cross section be measured at 7 and 8 TeV, and how does it compare to SM predictions?
• RQ4 What are the constraints on anomalous Wtb couplings and FCNC processes from single top quark production?
• RQ5 How will the higher center-of-mass energy in LHC Run II enhance the precision of top quark property measurements?

Key findings

• The large charge asymmetry measured at the Tevatron is resolved by including full NNLO QCD and electroweak NLO corrections, with no indication of new physics.
• No evidence for resonant top quark pair production is observed in LHC Run I data, but analysis strategies for boosted topologies are established and sensitive to new physics.
• The t-channel single top quark production cross section is measured with a relative uncertainty below 9.5% at √s = 7 and 8 TeV, in excellent agreement with SM predictions.
• The CMS collaboration observes Wt production at 6.1σ significance using 12.2 fb⁻¹ of data at √s = 8 TeV, with a measured cross section of 12.3 ± 5.4 pb.
• The ATLAS collaboration sets a 95% C.L. upper limit of 14.6 pb on s-channel single top quark production using 20.3 fb⁻¹ of 8 TeV data, consistent with SM expectations.
• LHC Run II is expected to significantly enhance sensitivity to top quark properties, including W-boson helicity, top quark polarization, and anomalous couplings, due to higher center-of-mass energy and improved statistics.