Unbinned deep learning jet substructure measurement in high Q² ep collisions at HERA

The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators with numerous applications in high energy particle and nuclear physics. Looking at electronproton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the k_T jet clustering algorithm. Results are reported at high transverse momentum transfer Q² > 150 GeV², and inelasticity 0.2 < y < 0.7. The analysis is also performed in sub-regions of Q², thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models.