[Paper Review] Combination of CDF and D0 results on the mass of the top quark using up to 9.7 fb$^{-1}$ at the Tevatron

R. C. Group|arXiv (Cornell University)|Jul 10, 2014

High-Energy Particle Collisions Research21 citations

TL;DR

This paper presents a precision combination of top quark mass measurements from the CDF and DØ experiments at Fermilab's Tevatron collider, using up to 9.7 fb⁻¹ of proton-antiproton collision data. By combining Run I and Run II results with careful treatment of statistical and systematic uncertainties—including correlations from jet energy scale and in situ calibration—the final Tevatron average top quark mass is determined as 174.34 ± 0.64 GeV/c², achieving a relative precision of 0.37%.

ABSTRACT

We summarize the current top-quark mass measurements from the CDF and D0 experiments at Fermilab. We combine published Run I (1992--1996) results with the most precise published and preliminary Run II (2001--2011) measurements based on data corresponding to up to 9.7 fb$^{-1}$ of $p\bar{p}$ collisions. Taking correlations of uncertainties into account, and combining the statistical and systematic uncertainties, the resulting preliminary Tevatron average mass of the top quark is $M_{top} = 174.34 \pm 0.64 ~GeV/c^2$, corresponding to a relative precision of 0.37%.

Motivation & Objective

• To improve the precision of the top quark mass measurement by combining the most up-to-date results from CDF and DØ experiments at the Tevatron.
• To account for correlations between systematic uncertainties across experiments, decay channels, and data runs to ensure a statistically consistent combination.
• To update the Tevatron average top quark mass using full Run II datasets and refined analysis techniques, including in situ jet energy calibration.
• To provide a benchmark for the top quark mass prior to the LHC era, enhancing consistency with global electroweak fits and testing the Standard Model.
• To quantify the dominant sources of systematic uncertainty, particularly in jet energy scale and signal modeling, to guide future improvements.

Proposed method

• Combines 12 top quark mass measurements: five Run I published results and seven Run II results (five published, two preliminary), all using up to 9.7 fb⁻¹ of integrated luminosity.
• Applies a multivariate combination method that accounts for correlations between statistical and systematic uncertainties across experiments and decay channels.
• Uses in situ jet energy calibration techniques in the $ι$+jets, all-jets, and MEt channels to reduce jet energy scale uncertainties, particularly for light and b-jets.
• Treats systematic uncertainties as Gaussian and combines them in quadrature with statistical uncertainties, using covariance matrices to model correlations.
• Performs consistency checks via $χ^2$ tests between different decay channels and between CDF and DØ measurements to validate the combination.
• Applies a weighted average that accounts for the full correlation matrix between all input measurements, ensuring minimal bias and optimal precision.

Experimental results

Research questions

• RQ1 What is the most precise combined value of the top quark mass from the Tevatron experiments CDF and DØ using the full Run II dataset?
• RQ2 How do correlations between systematic uncertainties—especially from jet energy scale and signal modeling—affect the final combined uncertainty?
• RQ3 Are the top quark mass measurements from different decay channels (e.g., $ι$+jets, $ι\ell$, all-jets, MEt) statistically consistent with one another?
• RQ4 How does the precision of the Tevatron average compare to previous combinations and the world average?
• RQ5 What are the dominant systematic uncertainties limiting the precision of the top quark mass measurement at the Tevatron?

Key findings

• The combined Tevatron average top quark mass is $ M_{\mathrm{t}} = 174.34 \pm 0.64\ \mathrm{GeV}/c^{2} $, representing a 26% improvement in precision over the previous 2013 combination.
• The relative precision of the result reaches 0.37%, limited primarily by systematic uncertainties in jet energy scale and signal modeling.
• The central value is 1.14 GeV/c² higher than the 2013 Tevatron average ($173.20 \pm 0.87$ GeV/c²), reflecting updated analysis and full Run II data.
• The $\chi^2$ test for consistency between CDF and DØ measurements yields $\chi^2 = 3.5/1$ (6.3% probability), indicating no significant tension between the two experiments.
• All pairwise comparisons between decay channels (e.g., $\ell$+jets vs. $\ell\ell$, $\ell$+jets vs. MEt) show consistent results, with $\chi^2$ probabilities ranging from 13% to 99%.
• The result is 1.00 GeV/c² higher than the world average and features 16% better precision, underscoring its importance in global electroweak fits.