A new observable to measure the top-quark mass at hadron colliders

TL;DR

The paper introduces a new, NLO-QCD-based observable for top-quark mass extraction at hadron colliders, using the normalized differential distribution of $t\bar{t} + 1\textnormal{-jet}$ production as a function of $\rho_s$ to probe $m_t^{\text{pole}}$. The method benefits from reduced PDF and scale uncertainties in the normalized ratio $\mathcal{R}(m_t^{\text{pole}}, \rho_s)$ and exhibits pronounced mass sensitivity in specific $\rho_s$ regions, while preserving a well-defined renormalization scheme. A comprehensive experimental viability study shows robustness against shower models, manageable jet-energy-scale uncertainties, and an unfolding strategy that is nearly mass-independent, projecting a total uncertainty around 1 GeV or below. Overall, the approach offers a complementary, theoretically controlled path to precise top-quark mass measurements with practical applicability to LHC data.

Abstract

A new method to measure the top-quark mass in high energetic hadron collisions is presented. We use theoretical predictions calculated at next-to-leading order accuracy in quantum chromodynamics to study the (normalized) differential distribution of the \ttbaronejet cross section with respect to its invariant mass $\sqrt{\sttj}$. The sensitivity of the method to the top-quark mass together with the impact of various theoretical and experimental uncertainties has been investigated and quantified. The new method allows for a complementary measurement of the top-quark mass parameter and has a high potential to become competitive in precision with respect to established approaches. Furthermore we emphasize that in the proposed method the mass parameter is uniquely defined through one-loop renormalization.

Figures (11)

• Figure 1: Comparison of different theoretical approaches to describe the $t\bar{t} + 1\textnormal{\normalsize -jet}$ production applied to various $p_T$ and $\eta$ distributions. The red band corresponds to the $t\bar{t} + 1\textnormal{\normalsize -jet}$ NLO at fixed order including the scale uncertainty. The continuous-blue and dotted-black line show the results obtained using POWHEG with $t\bar{t}$ and $t\bar{t} + 1\textnormal{\normalsize -jet}$ NLO calculations, respectively, and matched with the Pythia8 parton shower.
• Figure 2: Comparison between ${\@fontswitch\mathcal{R}}\xspace(m_t^{\hbox{\scriptsize pole}}\xspace,\rho_s\xspace)$ calculated at LO and NLO accuracy for a $m_t^{\hbox{\scriptsize pole}}\xspace=170$ GeV and using the CT09MC1 and CTEQ6.6 PDF sets, respectively. Below we show the ratio NLO/LO.
• Figure 3: Predictions for ${\@fontswitch\mathcal{R}}$ at NLO accuracy using two different PDF sets (CTEQ6.6, MSTW2008nlo) for $m_t^{\hbox{\scriptsize pole}}\xspace=170$GeV. For CTEQ6.6 the uncertainty due to scale variation is shown as band. The ratio between both predictions is shown together with the scale uncertainty.
• Figure 4: ${\@fontswitch\mathcal{R}}\xspace(m_t^{\hbox{\scriptsize pole}}\xspace,\rho_s\xspace)$ calculated at NLO accuracy for different masses $m_t^{\hbox{\scriptsize pole}}\xspace=160,\,170$ and $180$ GeV. For $m_t^{\hbox{\scriptsize pole}}\xspace=170$ GeV the scale and PDF uncertainties evaluated as discussed in the text are shown. The ratio with respect to the result for $m_t^{\hbox{\scriptsize pole}}\xspace=170$ GeV is shown in the lower plot.
• Figure 5: The sensitivity ${\@fontswitch\mathcal{S}}(\rho_s\xspace)$ of ${\@fontswitch\mathcal{R}}$ with respect to the top-quark mass as defined in Eq. (\ref{['eq:SDefinition']}).