[Paper Review] Top-quark mass measurements: review and perspectives

G. Cortiana|arXiv (Cornell University)|Oct 15, 2015

Particle physics theoretical and experimental studies78 references4 citations

TL;DR

This paper reviews top-quark mass measurements from the Tevatron and LHC, emphasizing their critical role in testing the Standard Model, constraining new physics, and assessing Higgs boson vacuum stability. It outlines methodologies, theoretical and experimental challenges, and projects that an overall precision of 200–300 MeV is achievable by LHC Run 2 and 3 through improved measurements and optimized multi-experiment combinations.

ABSTRACT

The top quark is the heaviest elementary particle known and its mass ($m_{ m top}$) is a fundamental parameter of the Standard Model (SM). The $m_{ m top}$ value affects theory predictions of particle production cross-sections required for exploring Higgs-boson properties and searching for New Physics (NP). Its precise determination is essential for testing the overall consistency of the SM, to constrain NP models, through precision electroweak fits, and has an extraordinary impact on the Higgs sector, and on the SM extrapolation to high-energies. The methodologies, the results, and the main theoretical and experimental challenges related to the $m_{ m top}$ measurements and combinations at the Large Hadron Collider (LHC) and at the Tevatron are reviewed and discussed. Finally, the prospects for the improvement of the $m_{ m top}$ precision during the upcoming LHC runs are briefly outlined.

Motivation & Objective

• To review the methodologies, results, and theoretical and experimental challenges in top-quark mass measurements at the Tevatron and LHC.
• To assess the impact of top-quark mass precision on Standard Model consistency tests and new physics constraints.
• To evaluate the role of the top quark in determining the stability of the electroweak vacuum via Higgs self-coupling evolution.
• To project future improvements in top-quark mass precision, particularly through multi-experiment combinations and refined Monte Carlo modeling.
• To explore alternative indirect determination methods using flavor physics observables and their potential for reducing theoretical ambiguities.

Proposed method

• Direct reconstruction of top-quark decay products using experimental data and Monte Carlo simulations to extract $ m_{\mathrm{top}}^\mathrm{MC} $.
• Calibration of $ m_{\mathrm{top}}^\mathrm{MC} $ against theoretical mass schemes, particularly the pole mass $ m_{\mathrm{top}}^\mathrm{pole} $, with associated uncertainties of ~1 GeV.
• Comparison of measured $ t\bar{t} $ differential cross-sections with theoretical predictions to reduce theoretical uncertainties in $ m_{\mathrm{top}} $ extraction.
• Use of common $ t\bar{t} $ Monte Carlo samples across experiments to assess systematic uncertainties and improve compatibility in uncertainty evaluations.
• Application of global electroweak fits to constrain $ m_{\mathrm{top}} $ and $ m_W $, incorporating both direct measurements and indirect constraints.
• Exploration of indirect $ m_{\mathrm{top}} $ determinations via flavor physics observables such as $ \Delta m_{B_s} $ and $ \mathcal{B}(B_s \to \mu^+\mu^-) $, sensitive to top-quark Yukawa coupling.

Experimental results

Research questions

• RQ1 How do current methodologies for top-quark mass measurement at the LHC and Tevatron affect the precision and theoretical interpretation of $ m_{\mathrm{top}} $?
• RQ2 To what extent does the uncertainty in identifying $ m_{\mathrm{top}}^\mathrm{MC} $ with $ m_{\mathrm{top}}^\mathrm{pole} $ limit the precision of top-quark mass determinations?
• RQ3 How does the precision of $ m_{\mathrm{top}} $ influence predictions about the stability of the electroweak vacuum and Higgs self-coupling evolution?
• RQ4 What improvements in precision are expected from future LHC runs, particularly through multi-experiment combinations and common Monte Carlo simulations?
• RQ5 Can indirect determinations of $ m_{\mathrm{top}} $ from flavor physics observables provide complementary and robust constraints, and what is their projected precision?

Key findings

• The top-quark mass is a fundamental parameter that significantly influences Higgs sector stability and electroweak vacuum lifetime, with the energy scale of instability varying by several orders of magnitude under a ±1.8 GeV change in $ m_{\mathrm{top}} $.
• Current direct measurements of $ m_{\mathrm{top}} $ are based on $ m_{\mathrm{top}}^\mathrm{MC} $, which is formally not a renormalized field theory parameter and requires careful interpretation relative to $ m_{\mathrm{top}}^\mathrm{pole} $, with an associated uncertainty of ~1 GeV.
• Future LHC runs are projected to achieve a combined top-quark mass precision of 200–300 MeV through improved individual measurements and optimized multi-experiment combinations.
• Indirect determinations from flavor observables such as $ \Delta m_{B_s} $ and $ \mathcal{B}(B_s \to \mu^+\mu^-) $ currently achieve ~8 GeV precision, with a projected reach of ~2 GeV with future improvements.
• The use of common $ t\bar{t} $ Monte Carlo samples across experiments is expected to enhance the understanding of systematic uncertainties and improve compatibility in uncertainty treatments.
• Complementary techniques—direct reconstruction and cross-section comparisons—will help reduce theoretical uncertainties in identifying $ m_{\mathrm{top}}^\mathrm{MC} $ with $ m_{\mathrm{top}}^\mathrm{pole} $, enabling more robust precision physics.