Recently, Professor Yin Hang's team from the College of Physics at Central China Normal University has made significant progress in the field of top quark physics. The team's leading research results, titled "Precise Measurements of Top Quark Production Cross Sections and Charge Asymmetry" [1], were published on June 1, 2026, in the international top-tier physics journal *Physical Review Letters*. Based on data from the LHCb experiment at the Large Hadron Collider (LHC), this study achieved the first measurement of top quark charge asymmetry in the forward rapidity region, obtaining the most precise experimental results in this kinematic region. This provides crucial experimental evidence for precisely testing the Standard Model of particle physics and exploring potential new physics. The results were previously featured in LHCb news, as reported in [2].

As the most massive elementary particle in the Standard Model, the top quark is crucial for understanding electroweak symmetry breaking and the Higgs mechanism. Its production process is highly sensitive to strong interactions and proton parton distribution functions, making it an important probe for testing the Standard Model. At the LHC, leading-order top quark pair production exhibits charge symmetry, while next-to-leading-order processes (quark-antiquark annihilation) introduce a slight asymmetry, which is significantly diluted in proton-proton collisions. However, in the forward rapidity region, the quark-initiated contribution is enhanced, making the asymmetry more pronounced. Therefore, precisely measuring this asymmetry is of great importance for testing higher-order QCD calculations and searching for new physics.

This study is based on data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, analyzing events in the final state containing a muon and a bottom-quark jet. Benefiting from the LHCb detector's unique acceptance in the forward rapidity region, the team achieved precise measurements of top quark production properties. Machine learning methods were employed for jet flavor tagging to extract high-purity signal events from the complex hadronic collision backgrounds, and major background processes were systematically studied, significantly improving measurement precision. Based on this analysis, the team measured, for the first time, the asymmetry in the production cross sections of top quarks and antitop quarks in the forward region (see figure below), which is consistent with Standard Model theoretical predictions.

Figure 1: Top quark charge asymmetry measured by the LHCb experiment

With the accumulation of higher-statistics data in the future, related measurements are expected to achieve further precision, enabling deeper investigations into the top quark production mechanism and the source of top quark charge asymmetry, as well as offering more possibilities for discovering signs of new physics beyond the Standard Model.

This research was supervised by Professor Yin Hang of Central China Normal University, with doctoral student Li Jiuzhao performing the primary data analysis and serving as the corresponding author of the paper. Dr. Menglin Xu from CERN made significant contributions to key analytical aspects such as heavy-flavor jet tagging. The research was supported by the General Program of the National Natural Science Foundation of China. The paper is authored collectively by the entire LHCb Collaboration, following the international convention in high-energy physics whereby authors are listed in alphabetical order by surname. This result follows the team's previous achievements in electroweak and top quark physics, including measurements of the weak mixing angle, Z boson mass (PRL), and Z boson production cross section and polarization (PRL).

Paper links:

[1] https://journals.aps.org/prl/abstract/10.1103/c1x7-f9wn

[2] https://lhcb-outreach.web.cern.ch/2026/02/15/chasing-top-quarks-and-higgs-bosons-with-artificial-intelligence/

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