Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Measurement of the differential $t$-channel production cross-section of single top quarks and top antiquarks at $\sqrt{s} = $13 TeV with the ATLAS detector

Maren Stratmann

TL;DR

This work measures differential $t$-channel single-top production cross-sections for $tq$ and $ar{t}q$ at $4$ TeV with the ATLAS detector, using the full Run-2 dataset to probe $p_T$ and $|y|$ dependencies and to test SM predictions. It employs a neural-network discriminator to enhance signal purity, and unfolds the observed distributions to parton level with Iterative Bayesian Unfolding, enabling direct comparison to fixed-order QCD, matrix-element generators, and PDFs. An EFT interpretation targets the four-fermion operator $O_{Qq}^{3,1}$, constraining its Wilson coefficient via a Bayesian EFTfitter to $-0.12 < C_{Qq}^{3,1}/mbda^2 < 0.12$ TeV$^{-2}$ at 95% CL. The results, including the first measurement of the $7q/ar{t}q$ cross-section ratio, provide precision tests of SM t-channel dynamics, inform PDF fits, and place limits on BSM EFT operators relevant for LHC phenomenology.

Abstract

Differential production cross-sections of single top quarks and top antiquarks are measured in proton-proton collisions at a centre-of-mass energy $\sqrt{s} = $13 TeV. The full Run-2 dataset collected by the ATLAS detector at the LHC in the years 2015-2018 is used. The differential cross-sections are measured as a function of the transverse momentum and absolute rapidity of the top (anti)quark. The measurement results are compared to predictions obtained from fixed order calculations, different matrix-element event generators and different parton distribution function sets. The results agree with the theoretical predictions within the measurement uncertainties. An effective field theory interpretation of the measurement sets constraints on the contribution of the four-fermion operator $O_{Qq}^{3,1}$.

Measurement of the differential $t$-channel production cross-section of single top quarks and top antiquarks at $\sqrt{s} = $13 TeV with the ATLAS detector

TL;DR

This work measures differential -channel single-top production cross-sections for and at TeV with the ATLAS detector, using the full Run-2 dataset to probe and dependencies and to test SM predictions. It employs a neural-network discriminator to enhance signal purity, and unfolds the observed distributions to parton level with Iterative Bayesian Unfolding, enabling direct comparison to fixed-order QCD, matrix-element generators, and PDFs. An EFT interpretation targets the four-fermion operator , constraining its Wilson coefficient via a Bayesian EFTfitter to TeV at 95% CL. The results, including the first measurement of the cross-section ratio, provide precision tests of SM t-channel dynamics, inform PDF fits, and place limits on BSM EFT operators relevant for LHC phenomenology.

Abstract

Differential production cross-sections of single top quarks and top antiquarks are measured in proton-proton collisions at a centre-of-mass energy 13 TeV. The full Run-2 dataset collected by the ATLAS detector at the LHC in the years 2015-2018 is used. The differential cross-sections are measured as a function of the transverse momentum and absolute rapidity of the top (anti)quark. The measurement results are compared to predictions obtained from fixed order calculations, different matrix-element event generators and different parton distribution function sets. The results agree with the theoretical predictions within the measurement uncertainties. An effective field theory interpretation of the measurement sets constraints on the contribution of the four-fermion operator .

Paper Structure

This paper contains 5 sections, 1 equation, 3 figures.

Table of Contents

  1. Introduction
  2. Analysis strategy
  3. Results
  4. Interpretation of the measurement
  5. Conclusion

Figures (3)

  • Figure 1: Systematic uncertainties on the absolute $tq$ production cross-section as a function of $p_\text{T}(t)$ATLAS-CONF-2025-011. The shaded band indicates the total uncertainty, obtained by adding all systematic uncertainties in quadrature. A further breakdown of the systematic uncertainties into different categories is given by the coloured bands.
  • Figure 2: Measurement results for differential cross-sections compared to theoretical predictions ATLAS-CONF-2025-011. \ref{['fig:Abs']} shows the normalised differential $tq$ cross-section as a function of $p_\text{T}(t)$ compared to theoretical predictions from different matrix-element generators and parton shower programs. \ref{['fig:Norm']} shows the absolute differential $\bar{t}q$ cross-section as a function of $|y(\bar{t})|$ compared to fixed order calculations done with MCFM Campbell:2020fhfCampbell:2021qgd at different orders in QCD. \ref{['fig:Ratio']} shows the ratio of $tq/\bar{t}q$ cross-sections as a function of $|y(t\text{ or }\bar{t})|$ compared to theoretical predictions calculated with different PDF sets.
  • Figure 3: Parameterisations for the expected relative change of the differential $tq$ production cross-section as a function of $C_{Qq}^{3,1}$ obtained from parton level predictions and by unfolding the detector level predictions ATLAS-CONF-2025-011. The uncertainties in the predictions are statistical uncertainties only. The dashed line indicates the measurement result over the theoretical prediction calculated with MCFM at NNLO and the uncertainty band includes the total uncertainty in the measurement result as well as the uncertainty in the theory prediction. The vertical shaded area shows the obtained 95% confidence interval.