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