Setting sail for HEP in Hamburg

9 November 2023
EPS conference participants
Together again Participants at the first in-person EPS conference since the COVID-19 pandemic. Credit: M Mayer/DESY

The European Physical Society Conference on High Energy Physics (EPS-HEP), which took place in Hamburg from 21 to 25 August, attracted around 900 physicists in-person and online to discuss a plethora of topics and results. An intense programme underlined both the vibrancy and diversity of the field, including the first evidence for a stochastic gravitational-wave background as well as the latest measurement of the anomalous magnetic moment of the muon – the latter sparking many discussions that continued during the breaks.

The participants were treated to many LHC Run 2 legacy results, as well as brand-new ones using freshly analysed Run 3 data. A large chunk of these results comprised precision measurements of the Higgs boson in view of gaining a deeper understanding of the origin of electroweak symmetry breaking. As the Higgs boson is deeply connected to many open questions potentially linked to physics beyond the Standard Model (SM), such as the origin of particle masses and flavour, studying it in the context of effective field theory is a particularly hot topic. A rich potential programme of “simplified” models for Higgs physics that can better quantify the reach of the LHC and offer new observables is also under development.

New frontiers

The ATLAS and CMS collaborations presented no fewer than 37 and 27 new preliminary results, respectively. Besides Higgs-sector physics, the experiments revealed their latest results of searches for physics beyond the SM, including new limits on the existence of supersymmetric and dark-matter particles. At the intensity frontier, the latest search for the ultra-rare decay K+ π+e+ee+e from the NA62 experiment placed upper limits on dark-boson candidate masses, underlining the powerful complementarity between CERN’s fixed-target and LHC programmes. The Belle II collaboration presented first evidence of the decay B+ K+νν, as well as the result of their R(X) = Br(B  Xτντ)/Br(B  Xℓν) measurement – the first at a B factory. The LHCb collaboration also presented an update of its recent R(D*) = Br(B  D*τντ)/Br(B  D*ν) measurement. Another highlight was LHCb’s observation of the hypernuclei antihypertriton and hypertriton.

Intense discussions took place on novel and potentially game-changing accelerator concepts

The state of the art in neutrino physics was presented, covering the vast landscape of experiments seeking to shed light on the three-flavour paradigm as well as the origin of the neutrino masses and mixings. So far, analyses by T2K and NOvA show a weak preference for a normal mass ordering, while the inverted mass ordering is not yet ruled out. With a joint analysis between T2K and NOvA in progress, updates are expected next year. At CERN the FASER experiment, which made the first observation of muon neutrinos at a collider earlier this year, presented the first observation of collider electron neutrinos. Looking outwards, a long-awaited discovery of galactic neutrinos was presented by IceCube.

The current FCC feasibility status was presented, along with that of other proposed colliders that could serve as Higgs factories. The overarching need to join forces between the circular- and linear-collider communities and to use all the gained knowledge for getting at least one accelerator approved was reflected during the discussions and many talks, as were the sustainability and energy consumption of detector and accelerator concepts. Intense discussions took place on novel and potentially game-changing accelerator concepts, such as energy recovery technologies or plasma acceleration. While not yet ready to be used on a large scale, they promise to have a big impact on the way accelerators are built in the future. Beyond colliders, the community also looked ahead to the DUNE and Hyper-Kamiokande experiments, and to proposed experiments such as the Einstein Telescope and those searching for axions.

A rich social programme included a public lecture by Andreas Hoecker (CERN) about particle physics at the highest energies, a concert with an introduction to the physics of the organ by Wolfgang Hillert (University of Hamburg), as well as an art exhibition called “High Energy” and a Ukrainian photo exhibition depicting science during times of war.

The next EPS-HEP conference will take place in 2025 in Marseille.

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