If you have not yet noticed, Particle Physics is going through a very critical period. The energy frontier—also known as the Large Hadron Collider (LHC)—has reached its midpoint after it started in 2009 and is expected to finish sometimes in the early 40ies. From afar this does not seem so alarming because there is ‘plenty of time’, over 15 years for sure, but considering the timescales to construct massive projects like the LHC or any major followup project that would keep the energy frontier thriving it is becoming increasingly urgent to make a decision. The community and funding agency know this and one workshop chases the next and informs the community and the various agencies about the status and the potentials of ‘the next big project’.
IN the US there is the Particle Physics Project Prioritization Panel which released its latest report in December 2023 and now there will be the the European Strategy making a statement about the future. The timeline for the decision is set for a while now but we are entering the phase when the reports come together. Last studies are being finalized and the US reports for the various projects are being composed. From the outside this might seem like a slow moving train with very little really new information, but on the inside at the workshops and conferences a lot of arguments in all different directions are being made. Each large scale project has many aspects and complications that only after some study come to light and have to be weight against each other. From the discussions in the P5 and the resulting report, the LHC remains the highest priority (Recommendation 1a)
HL-LHC (including the ATLAS and CMS detectors, as well as the Accelerator Upgrade Project) to start addressing why the Higgs boson condensed in the universe (reveal the secrets of the Higgs boson, section 3.2), to search for direct evidence for new particles (section 5.1), to pursue quantum imprints of new phenomena (section 5.2), and to determine the nature of dark matter (section 4.1).
as expected, and the next big energy frontier project is a ‘offshore Higgs Factory’ (Recommendation 2c). Offshore just implies a Higgs factory that is not build inside the US. Two explicit options are mentioned: the FCC-ee and the ILC.
An offshore Higgs factory, realized in collaboration with international partners, in order to reveal the secrets of the Higgs boson. The current designs of FCC-ee and ILC meet our scientific requirements. The US should actively engage in feasibility and design studies. Once a specific project is deemed feasible and well-defined (see also Recommendation 6), the US should aim for a contribution at funding levels commensurate to that of the US involvement in the LHC and HL-LHC, while maintaining a healthy US onshore program in particle physics (section 3.2).
Given the P5 report, it is expected that the European Strategy in Particle Physics will give a strong nod to the FCC-ee options, which is presently the flagship of the future study effort at CERN. The US is providing important input to the study and the European colleges expect the US to strongly support the FCC-ee option of the Higgs Factory at CERN. The signs for this to happen look good as the US has recently signed a statement of intent to work together with CERN on a future FCC Higgs Facility “should the CERN Member States determine the project feasible”. See below the timeline for the report to come together.
