Physics Briefing Book

TL;DR

The Briefing Book synthesizes the European Strategy Update process for strong-interaction physics, outlining how bottom-up inputs are transformed into a program that integrates QCD theory, hadronic structure, and heavy-ion physics across colliders and fixed-target facilities. It emphasizes precision QCD through $N^3LO$ calculations, advanced PDFs and LQCD, and the pursuit of three-dimensional nucleon structure via TMDs and GPDs, with ep and eA colliders (e.g., LHeC, FCC-eh, EIC) playing a central role. The document highlights hot/dense QCD and QGP tomographic studies at current and future energies, the synergy between collider and fixed-target approaches, and the cross-disciplinary impact on astroparticle and neutrino physics, underscoring the need for continued theory development, MC improvements, and high-statistics lattice simulations. Together, these efforts aim to sharpen SM predictions, probe potential new physics, and deepen our understanding of the strong interaction across all scales.

Abstract

The European Particle Physics Strategy Update (EPPSU) process takes a bottom-up approach, whereby the community is first invited to submit proposals (also called inputs) for projects that it would like to see realised in the near-term, mid-term and longer-term future. National inputs as well as inputs from National Laboratories are also an important element of the process. All these inputs are then reviewed by the Physics Preparatory Group (PPG), whose role is to organize a Symposium around the submitted ideas and to prepare a community discussion on the importance and merits of the various proposals. The results of these discussions are then concisely summarised in this Briefing Book, prepared by the Conveners, assisted by Scientific Secretaries, and with further contributions provided by the Contributors listed on the title page. This constitutes the basis for the considerations of the European Strategy Group (ESG), consisting of scientific delegates from CERN Member States, Associate Member States, directors of major European laboratories, representatives of various European organizations as well as invitees from outside the European Community. The ESG has the mission to formulate the European Strategy Update for the consideration and approval of the CERN Council.

Figures (7)

• Figure 1: Kinematic $(x, Q^2)$ plane probed in $e-p$ (left) and $e-A$ processes (right): existing data compared to proposed particle and nuclear DIS facilities Britzger:2017dEnterria:2007jwb.
• Figure 2: The QCD phase diagram in the temperature -- baryochemical potential plane. The band is from LQCD calculations Bazavov:2018mes, the points from statistical hadronisation model fits to hadron yields in heavy-ion collisions over a broad range of collision energy (updated from Ref. Andronic:2017pug).
• Figure 3: Comparison among the matched normalised distributions at: N$^3$LL+NNLO, NNLL+NNLO, and the pure NNLO of the Higgs-boson transverse-momentum spectrum at the LHC Bizon:2017rah.
• Figure 4: Different PDFs as obtained at NNLO level (NNPDF3.1) from Ref. Ball:2017nwa, evaluated at $\mu^2=10~{\rm GeV}^2$ (left) and $\mu^2=10^4~{\rm GeV}^2$ (right).
• Figure 5: The impact of the LHC data on the NNPDF3.1 NNLO PDFs for the down and charm quarks Ball:2017nwa.