First combination of Tevatron and LHC measurements of the top-quark mass

TL;DR

This study delivers the first global combination of top-quark mass measurements from the Tevatron and LHC using BLUE, aggregating 11 precise inputs from CDF, D0, ATLAS, and CMS across multiple ttbar final states. By carefully categorising and correlating systematic uncertainties—especially JES and modelling effects—and validating with stability tests, it achieves m_top = 173.34 ± 0.27 (stat) ± 0.71 (syst) GeV (0.76 GeV total). The analysis highlights the prominent role of JES and modelling uncertainties, demonstrates the method’s robustness to correlation assumptions, and underscores the need for theoretical clarity on the relation between MC top mass and the pole mass. Together, the results provide a more precise, globally-consistent top-quark mass estimate and establish a framework for future cross-experiment combinations as datasets grow.

Abstract

We present a combination of measurements of the mass of the top quark, $m_{\rm top}$, performed by the CDF and D0 experiments at the Tevatron collider and the ATLAS and CMS experiments at the Large Hadron Collider (LHC). The Tevatron data correspond to an integrated luminosity of up to 8.7 fb${^{-1}}$ of proton-antiproton collisions from Run II of the Tevatron at a centre-of-mass energy of 1.96 TeV. The LHC data correspond to an integrated luminosity of up to 4.9 fb${^{-1}}$ of proton-proton collisions from the run at a centre-of-mass energy of 7 TeV. The combination includes measurements in the $t\bar t\to$ lepton+jets, $t\bar t\to$ dilepton, $t\bar t\to$ all jets and $t\bar t\to$ $E_{\rm T}^{\rm miss}$+jets final states. The resulting combined measurement of $m_{\rm top}$ is $173.34 \pm 0.27 \mbox{(stat)} \pm 0.71 \mbox{(syst)}$ GeV, with a total uncertainty of $0.76$ GeV.

Figures (6)

• Figure 1: (a): Input measurements and result of their combination (see also Table \ref{['tab:syscat']}), compared with the Tevatron and LHC combined $m_{\mathrm{top}}$ values TEV2013LHC2013. With respect to Ref. TEV2013 only a partial set of Tevatron $m_{\mathrm{top}}$ measurements is used in the world combination (see Section \ref{['sec:input']}). For each measurement, the total uncertainty, the statistical and the iJES contributions (when applicable), as well as the sum of the remaining uncertainties are reported separately. The iJES contribution is statistical in nature and applies only to analyses performing in situ () jet energy calibration procedures. The grey vertical band reflect the total uncertainty on the combined $m_{\mathrm{top}}$ value. Panels (b) and (c) show, respectively, the BLUE combination coefficients and pulls of the input measurements.
• Figure 2: Comparison of the world $m_{\mathrm{top}}$ combination result with the individual $m_{\mathrm{top}}$ determinations per decay channel, experiment, and collider. Results are compared with the Tevatron and LHC combined $m_{\mathrm{top}}$ values from Refs. TEV2013LHC2013. The grey vertical band reflect the total uncertainty on the combined $m_{\mathrm{top}}$ value.
• Figure 3: Variation of the combined $m_{\mathrm{top}}$ result (a,c) and its total uncertainty (b,d) as a function of variations in the correlation assumptions. (a,b) $\rho_{\rm EXP}$, $\rho_{\rm LHC}$, $\rho_{\rm TEV}$ and $\rho_{\rm COL}$ are varied simultaneously using a multiplicative factor $f$ in the range [0,1] (open light blue dots). Separate variations of each correlation coefficient in the same range, are reported by the blue (filled dots), orange (filled triangles), red (filled squares) and the grey (open triangles) curve, respectively. (c,d) Stability of the world combination under variations of the default assumptions on the correlation for selected uncertainty sources. The sensitivity of the combination to different scenarios concerning the treatment of the hadronisation systematics is also shown. See text for details.
• Figure 4: Comparison of the standard combination results with the correlated $m_{\mathrm{top}}$ determinations (parameter values in Tables \ref{['tab:channels']}, \ref{['tab:exp']} and \ref{['tab:col']}) per decay channel, experiment, and collider. The grey vertical band reflect the total uncertainty on the combined $m_{\mathrm{top}}$ value.
• Figure 6: Variation of the combined $m_{\mathrm{top}}$ value (a, c, e) and of its uncertainty (b, d, f) for three different correlation assumptions for each uncertainty category ($f\cdot \rho$, with $f=0.8,~0.5$, and $0$). Variation of $\rho_{\rm EXP}$, $\rho_{\rm TEV}$ and $\rho_{\rm LHC}$ are reported by the top, middle and bottom panels, respectively.