Description
This work establishes a reproducible workflow to study jet substructure using public CMS Open Data from the LHC. Using the JetHT Run2016G MiniAOD dataset, we extract AK4 (anti-$k_t$, $R=0.4$) jet kinematics and constituent-level information and focus on a hard regime ($p_{T,\text{jet}} > 200~\mathrm{GeV}$) to probe perturbative QCD with reduced non-perturbative and pileup sensitivity. We reconstruct the jet branching history by re-clustering constituents with the Cambridge--Aachen algorithm and performing Lund declustering to build primary and secondary Lund jet planes. The resulting average Lund-plane densities show the expected kinematic triangular structure and radiation patterns, while SoftDrop grooming ($\beta=0$, $z_\text{cut}=0.1$) yields the anticipated migration from soft wide-angle activity toward harder, more collinear emissions. Building on this framework, we explore two observables sensitive to collinear spin correlations. The Lund-based azimuthal angle $\Delta\psi_{12}$ between the planes of the hardest primary and secondary branchings, which exhibits the characteristic $\cos(2\Delta\psi_{12})$ periodicity with a negative modulation and a hadron-collision adaptation of the three-point energy correlator (EEEC), whose $\Delta\psi$ distribution follows a $\cos(2\Delta\psi)$-like modulation with positive sign over full angular integration but changes markedly under restricted angular ranges, indicating non-trivial dependence on integration choices. These results demonstrate that CMS Open Data enables meaningful, substructure-level studies of QCD spin-interference effects, while motivating further validation of angle definitions, comparisons to simulation and detector-level effects, optimized EEEC computation, and flavour-tagged measurements.
| Field of Research/Work | Particles and Fields |
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