The CMS Experiment has unveiled its most precise and comprehensive measurement of the Higgs boson to date, utilising LHC Run 2 data collected between 2016 and 2018. This significant legacy combination of Higgs boson studies confirms theories regarding the origin of mass in the Universe with a 5% precision for its production rate. Scientists achieved this by statistically combining measurements from all accessible Higgs boson decay channels and production modes. Furthermore, the experiment employed Simplified Template Cross Sections (STXS) to map the Higgs boson's behaviour across 32 distinct categories, and interpreted these findings using Standard Model Effective Field Theory (SMEFT) to search for new physics in a model-independent way, examining 43 different SMEFT interactions. While largely confirming the Standard Model, the results also show intriguing small deviations in high-momentum regions, which could hint at physics beyond the current understanding.

Links:

- https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIG-21-018/index.html

- https://cms.cern/news/pieces-precision-building-higgs-bosons-clearest-portrait-date

he ATLAS Experiment at CERN has embraced modern AI techniques to revolutionise jet flavour tagging, a crucial process in analysing particle collisions. A new algorithm called GN2, powered by a Transformer neural network, directly analyses information from particle tracks and jets, eliminating the need for previous, hand-crafted algorithms. This advancement significantly improves the identification of b-jets and c-jets, which are vital for Standard Model measurements and the search for new physics phenomena. The ATLAS Collaboration has established robust pipelines to integrate and train these AI algorithms, leading to a substantial leap in performance and offering deeper insights into the physics signatures learned by the model. This innovative approach is already having a significant impact on ATLAS physics research, including enhancing the precision of Higgs boson studies and the search for new particles.

Paper link: https://arxiv.org/pdf/2505.19689

The CMS Collaboration's "An all-round boosted chase for supersymmetry" explores the concept of supersymmetry (SUSY), a theoretical extension of the Standard Model of particle physics. The article details how scientists at CERN's CMS Experiment are searching for superparticles by analysing final states that include Lorentz-boosted objects, which are formed when heavy superparticles decay into lighter, high-momentum particles. This new "razor boost" analysis broadens the search to 25 distinct final states, including boosted W, Z, Higgs bosons, top quarks, and uniquely, boosted leptonic jets, using machine learning and razor kinematic variables to identify potential SUSY signals. Although no significant deviations from Standard Model predictions were observed, the findings have allowed the collaboration to set strong limits on superparticle production rates and masses within various SUSY models, with further interpretations of complete SUSY models ongoing.

Links: https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/SUS-23-014/index.html

The current episode discusses a research paper from the ATLAS Collaboration concerning the evaluation of statistical uncertainties in the jet η-intercalibration method for the ATLAS experiment at CERN's Large Hadron Collider. The paper, identified as ATL-PHYS-PUB-2025-027, explains a new approach utilising the bootstrap method to determine calibration factor uncertainties and their correlations more accurately. This innovative technique is compared against previous methods, with figures illustrating distributions, uncertainty ratios, and correlation matrices. Additionally, the paper introduces a method for quantifying the statistical compatibility of jet observables within the calibration procedure, employing a pull statistic to assess robustness.

Links: https://cds.cern.ch/record/2935135/files/ATL-PHYS-PUB-2025-027.pdf

In this episode, we discuss the details of the CMS experiment's innovative advancement in particle detection, specifically focusing on its enhanced ability to identify highly collimated electron-positron pairs. Previously, the CMS detector struggled to differentiate these pairs when they travelled too closely, often registering them as a single particle. To overcome this, the CMS Collaboration developed a new machine learning-based technique that significantly improves the detector's resolution, enabling it to distinguish pairs with extremely small angular separations. The text explains how this new method has been rigorously tested and validated using both simulations and real-world data, confirming its efficacy in energy measurement and consistency. This improved capability will allow CMS to conduct more precise searches for new phenomena beyond the Standard Model, particularly theories predicting the existence of lightweight bosons that decay into such electron-positron pairs.

Read more about it in: https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/EGM-24-002/index.html

This episode details the ATLAS Collaboration's ongoing research into rare Higgs boson decays at the Large Hadron Collider (LHC), specifically focusing on decays to muons (H→μμ) and to a Z boson and a photon (H→Zγ). These studies, utilising data from LHC Run 3 (2022–2024) and combined with Run 2 (2015–2018) data, aim to test the Standard Model by precisely measuring these infrequent processes. The documents explain the experimental methods used to identify these rare events, including sophisticated data analysis techniques and event categorisation, and present the statistical significance of the observed evidence. The findings demonstrate improved sensitivity and contribute to a more comprehensive understanding of the Higgs boson's properties.

Papers:

https://arxiv.org/pdf/2507.03595

https://cds.cern.ch/record/2937635/files/ATLAS-CONF-2025-007.pdf

In this episode, we detail experimental particle physics research conducted by the ATLAS and CMS Collaborations at the Large Hadron Collider (LHC), specifically focusing on proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV. Both collaborations investigate top-antitop (tt) pair production, with a particular emphasis on the kinematic threshold region where quasi-bound tt states are expected to form. The ATLAS experiment reports an observed excess of events over standard perturbative Quantum Chromodynamics (pQCD) predictions, consistent with the formation of these colour-singlet, S-wave quasi-bound tt states, and quantifies this excess with a significance of 7.7 standard deviations. The CMS experiment also notes a similar enhancement at the tt threshold and reproduces mild tension regarding spin correlation measurements, ultimately establishing the presence of a pseudoscalar excess at the tt production threshold with a significance exceeding five standard deviations. Both papers describe their detector apparatus, event reconstruction methods, background estimations, and systematic uncertainties, utilising Monte Carlo simulations to model various processes and validate their findings.

ATLAS paper: https://cds.cern.ch/record/2937636/files/ATLAS-CONF-2025-008.pdf

CMS paper: https://arxiv.org/pdf/2503.22382

This episode details an experiment conducted by the ATLAS Collaboration using Large Hadron Collider data from 2015-2018. The research investigates the CP properties of the Higgs boson in its vector-boson fusion production mode, specifically focusing on its decay into two tau leptons. Utilising the Optimal Observable method and an effective field theory framework, the study aims to detect CP-violating interactions between the Higgs boson and electroweak gauge bosons. While no deviations from the Standard Model (which predicts a CP-even Higgs boson) were observed, the analysis provides stringent limits on strength parameters that describe potential beyond-Standard Model physics. The paper compares these findings with previous ATLAS and CMS Collaboration results, contributing to the ongoing effort to understand the fundamental nature of the Higgs boson.

Link to arxiv: https://arxiv.org/abs/2506.19395