Impact of High-Precision Top-Quark Pair Production Measurements on Proton PDFs and the Role of aN3LO QCD and NLO EW Corrections on 𝑡¯𝑡 Observables

Core Concepts

High-precision top-quark pair production measurements at the LHC are crucial for constraining proton PDFs, particularly the gluon PDF at large momentum fractions. Additionally, incorporating higher-order QCD and electroweak corrections significantly improves the accuracy of theoretical predictions for top-quark pair production observables.

Abstract

Bibliographic Information:

Ablat, A., Dulat, S., Guzzi, M., Hou, T.-J., Kidonakis, N., Sitiwaldi, I., Tonero, A., Xie, K., & Yuan, C.-P. (2024). Progress in top-quark pair production cross section calculations and impact on parton distribution functions of the proton. In 12th Edition of the Large Hadron Collider Physics Conference (LHCP2024). [Conference Presentation]. https://pos.sissa.it/

Research Objective:

This conference proceeding aims to investigate the impact of recent high-precision top-quark pair production measurements at the LHC on the determination of proton Parton Distribution Functions (PDFs) and to assess the effect of approximate next-to-next-to-next-to-leading order (aN3LO) QCD corrections combined with next-to-leading order (NLO) electroweak (EW) corrections on 𝑡¯𝑡 observables.

Methodology:

The authors utilize a combination of experimental data analysis and theoretical calculations. They incorporate high-precision top-quark pair production measurements from the ATLAS and CMS experiments at the LHC. For theoretical predictions, they employ various tools and techniques, including fastNNLO tables, MATRIX code, APPLgrid tables with MCFM, and MadGraph_aMC@NLO, to compute cross sections and differential distributions at different orders of QCD and electroweak theory.

Key Findings:

• Including recent 𝑡¯𝑡 measurements in global QCD analyses leads to a noticeable impact on the gluon PDF, especially at large values of the momentum fraction (x), where constraints from previous data were weaker.
• Two optimal combinations of 𝑡¯𝑡 measurements, CT18+nTT1 and CT18+nTT2, are identified, which maximize the sensitivity to PDFs and minimize tensions among data sets.
• Theoretical predictions for 𝑡¯𝑡 total and differential cross sections are significantly improved by incorporating aN3LO QCD corrections and NLO EW corrections.
• The aN3LO QCD corrections generally enhance the predicted cross sections, while NLO EW corrections play a crucial role at large transverse momenta.

Main Conclusions:

The study highlights the importance of high-precision top-quark pair production measurements at the LHC for refining our understanding of proton structure and for making accurate theoretical predictions for 𝑡¯𝑡 observables. The inclusion of higher-order QCD and electroweak corrections is essential for achieving precision in theoretical calculations, paving the way for more stringent tests of the Standard Model and searches for new physics at the LHC.

Significance:

This research significantly contributes to the field of particle physics by improving the accuracy of theoretical predictions for top-quark pair production, a crucial process for understanding the Standard Model and searching for new physics at the LHC. The findings have implications for future PDF determinations and for interpreting experimental results at current and future colliders.

Limitations and Future Research:

The study primarily focuses on the impact of LHC data at 13 TeV. Future research could explore the impact of data at other energies and investigate the interplay of 𝑡¯𝑡 measurements with other processes sensitive to PDFs. Further theoretical advancements, such as the calculation of complete N3LO QCD corrections, would further enhance the precision of predictions.

Stats

The study analyzes data from the ATLAS and CMS experiments at the LHC at a collision energy of 13 TeV.
The CT18+nTT1 dataset includes the rapidity distribution of the top-quark pair (𝑦𝑡¯𝑡) from ATLAS (hadronic and lepton+jet channels) and CMS (dilepton channel), and the invariant mass distribution of the top-quark pair (𝑚𝑡¯𝑡) from CMS (lepton+jet channel).
The CT18+nTT2 dataset is similar to CT18+nTT1 but replaces the ATLAS lepton+jet 𝑦𝑡¯𝑡 distribution with a combination of 𝑦𝑡¯𝑡, 𝑦𝐵𝑡¯𝑡 (boosted topology rapidity), 𝑚𝑡¯𝑡, and 𝐻𝑡¯𝑡𝑇 (scalar sum of transverse momenta).
The overall quality-of-fit for both CT18+nTT1 and CT18+nTT2 is comparable to the CT18 baseline, with 𝜒2/𝑁𝑝𝑡≈1.16.

Quotes

Key Insights Distilled From

Progress in top-quark pair production cross section calculations and impact on parton distribution functions of the proton

by Alim Ablat, ... at arxiv.org 11-04-2024

https://arxiv.org/pdf/2411.00055.pdf

Deeper Inquiries

How will future high-luminosity data from the High-Luminosity LHC (HL-LHC) further impact the determination of proton PDFs, particularly the gluon PDF at high x?

Answer: The High-Luminosity LHC (HL-LHC) is expected to deliver an unprecedented amount of data, significantly exceeding the current dataset. This will profoundly impact the determination of proton PDFs, especially the gluon PDF at high x, in several ways:

Reduced Uncertainties: The vast HL-LHC dataset will drastically reduce statistical uncertainties in experimental measurements. This is crucial for processes like top-quark pair production, which are directly sensitive to the gluon PDF. Smaller uncertainties in measurements translate to tighter constraints on the gluon PDF, particularly in the high-x region where current knowledge is limited.

Access to High-x Region: The increased collision energy and luminosity of the HL-LHC will provide access to a wider kinematic range, probing the PDFs at higher values of x. This is essential for pinning down the gluon PDF at high x, which is crucial for understanding the dynamics of gluons within the proton and for making accurate predictions for other high-energy processes.

Improved Constraints from Differential Distributions: The HL-LHC will enable the measurement of differential cross sections with much higher precision. These distributions, such as the top quark transverse momentum (pT) and rapidity distributions, offer a more detailed picture of the underlying physics and provide stronger constraints on PDFs than total cross sections alone.

Combined Analyses with Other Processes: The HL-LHC will provide high-precision data for a wide range of processes. Combining data from top-quark pair production with measurements from other processes like jet production, especially those sensitive to different x-ranges, will allow for a more comprehensive and robust determination of the gluon PDF across a broader kinematic range.
In summary, the HL-LHC's high-luminosity data will be instrumental in significantly improving our understanding of the gluon PDF at high x, leading to more precise theoretical predictions for a wide range of processes at the energy frontier of particle physics.

Could potential deviations between experimental measurements and theoretical predictions in top-quark pair production at very high energies hint at new physics beyond the Standard Model?

Answer: Yes, potential deviations between experimental measurements and precise theoretical predictions in top-quark pair production at very high energies could indeed provide compelling hints of new physics beyond the Standard Model (BSM). Here's why:

Top Quark as a Sensitive Probe: The top quark, being the heaviest known fundamental particle, is extraordinarily sensitive to new physics at high energy scales. Any new particles or interactions coupling to the top quark could modify the rates and kinematic distributions of top-quark pair production, leading to observable discrepancies with Standard Model predictions.

Precision Measurements and Calculations: As highlighted in the context, significant progress has been made in both experimental measurements and theoretical calculations for top-quark pair production. This high level of precision allows for stringent tests of the Standard Model, making even small deviations from expectations potentially significant.

Examples of BSM Scenarios: Several BSM scenarios could manifest as deviations in top-quark pair production. These include:

New heavy particles: Particles like heavier gauge bosons (W', Z') or new quarks could decay into top-quark pairs, enhancing the production rate or altering kinematic distributions.
Resonances: New resonant states decaying to top-quark pairs, such as those predicted in some extensions of the Higgs sector, could create distinctive peaks in the invariant mass distribution of the top-quark pair.
Modified Top Quark Couplings: BSM physics could modify the couplings of the top quark to other particles, such as the Higgs boson or the electroweak gauge bosons, leading to deviations in production rates and distributions.

Discriminating New Physics: Observing deviations alone is not enough; careful analysis is crucial to differentiate between statistical fluctuations, systematic uncertainties, and genuine signs of new physics. However, the high precision achievable at the LHC, combined with the development of advanced analysis techniques, enhances our ability to disentangle these effects and potentially uncover new physics.
Therefore, while agreement between theory and experiment would further solidify the Standard Model, any significant deviations in top-quark pair production at very high energies would be a strong indicator of new physics, potentially opening exciting new avenues for exploration in particle physics.

How can the insights gained from studying top-quark pair production at the LHC be applied to other areas of particle physics, such as the search for dark matter or the study of the Higgs boson?

Answer: The insights gained from studying top-quark pair production at the LHC have far-reaching implications and can be applied to other areas of particle physics, including the search for dark matter and the study of the Higgs boson, in several ways:

Improved Understanding of the Proton Structure: As emphasized in the context, top-quark pair production is a powerful tool for probing the structure of the proton, particularly the gluon PDF. A precise knowledge of PDFs is essential for making accurate predictions for a wide range of processes, including those relevant for dark matter searches and Higgs boson studies.

Background Estimation for New Physics Searches: Top-quark pair production is a significant background process in many searches for new physics, including those for dark matter and new Higgs bosons. Precise measurements and theoretical predictions of top-quark pair production are crucial for accurately estimating and subtracting this background, enhancing the sensitivity to potential new physics signals.

Testing Theoretical Tools and Techniques: The theoretical calculations and experimental techniques developed for top-quark pair production, such as higher-order perturbative QCD calculations and advanced analysis methods, are directly applicable to other areas of particle physics. These tools and techniques can be used to improve predictions for other processes, including those relevant for dark matter and Higgs boson studies.

Indirect Constraints on New Physics: Precise measurements of top-quark properties, such as its mass and couplings, can indirectly constrain models of new physics. For example, some dark matter models predict modifications to the Higgs boson's coupling to the top quark, which could be constrained by precise measurements of top-quark pair production in association with a Higgs boson.

Synergies with Other LHC Measurements: Combining insights from top-quark pair production with measurements from other LHC experiments, such as those studying Higgs boson decays or searching for dark matter, can provide a more comprehensive picture of particle physics at the TeV scale. This combined approach can lead to a deeper understanding of the fundamental laws of nature and potentially uncover new connections between seemingly disparate phenomena.
In conclusion, the study of top-quark pair production at the LHC provides valuable insights and tools that extend beyond the realm of top-quark physics. These insights are crucial for advancing our understanding of other fundamental questions in particle physics, including the nature of dark matter and the properties of the Higgs boson, paving the way for new discoveries and a more complete picture of the universe at its most fundamental level.