Narrow Results

Jet substructure in heavy-ion collisions is a rapidly evolving area with lots of intriguing new measurements. This contribution presents a selection of recent jet-substructure measurements from experiments at the LHC, in particular, soft-drop groomed radii of jets and reclustered large-radius jets from ATLAS, jet axis difference and generalized jet angularities from ALICE, as well as dijet shapes and b-jet shapes from the CMS experiment.

For most high-precision experiments in particle physics, it is essential to know the luminosity at highest accuracy. The luminosity is determined by the convolution of particle densities of the colliding beams. In special van der Meer transverse beam separation scans, the convolution function is sampled along the horizontal and vertical axes with the purpose of determining the beam convolution and getting an absolute luminosity calibration. For this purpose, the van der Meer data of luminometer rates are separately fitted in the two directions with analytic functions giving the best description. With the assumption that the 2D convolution shape is factorizable, one can calculate it from the two 1D fits. The task of XY factorization analyses is to check this assumption and give a quantitative measure of the effect of nonfactorizability on the calibration constant to improve the accuracy of luminosity measurements.

We perform a dedicated analysis to study XY nonfactorization on proton–proton data collected in 2022 at $\sqrt{s}=13.6$TeV by the CMS experiment [The CMS Collab., Luminosity measurement in proton-proton collisions at $\sqrt{s}=13.6$ TeV in 2022 at CMS (2024). A detailed examination of the shape of the bunch convolution function is presented, studying various biases, and choosing the best-fit analytic 2D functions to finally obtain the correction and its uncertainty.

The timeline of the expansion rate ultimately defines the interplay between high-energy physics, astrophysics and cosmology. The guiding theme of this topical review is provided by the scrutiny of the early history of the space–time curvature through the diffuse backgrounds of gravitational radiation that are sensitive to all the stages of the evolution of the plasma. Due to their broad spectrum (extending from the aHz region to the THz domain) they bridge the macroworld described by general relativity and the microworld of the fundamental constituents of matter. It is argued that during the next score year the analysis of the relic gravitons may infirm or confirm the current paradigm where a radiation plasma is assumed to dominate the whole post-inflationary epoch. The role of high frequency and ultra-high frequency signals between the MHz and the THz is emphasized in the perspective of quantum sensing. The multiparticle final state of the relic gravitons and its macroscopic quantumness is also discussed with particular attention to the interplay between the entanglement entropy and the maximal frequency of the spectrum.

This report presents the status of the use of World-Wide Web (WWW) in High Energy Physics (HEP) experiments. The use of WWW in general, for ‘Online Datataking Systems’ and for ‘Offline Analysis Systems’ is discussed. In each of these cases the current use and a possible outlook for the future is described. Statistics on the actual use of WWW in HEP experiments as well as its current problems and future needs are also presented.

I discuss how global QCD fits of parton distribution functions (PDFs) can make the somewhat separated fields of high-energy particle physics and lower energy hadronic and nuclear physics interact to the benefit of both. I review specific examples of this interplay from recent works of the CTEQ-Jefferson Lab collaboration, including hadron structure at large parton momentum and gauge boson production at colliders. I devote particular attention to quantifying theoretical uncertainties arising in the treatment of large partonic momentum contributions to deep inelastic scattering (DIS) observables, and to discussing the experimental progress needed to reduce these.