High Energy Physics Seminars

Di-Higgs production directly probes the Higgs self-coupling, a crucial parameter for testing the Higgs potential and the Standard Model. With a small cross section of ∼33 fb, it remains currently unobserved at the LHC. The High-Luminosity LHC (HL-LHC), expected to start in 2030, will deliver 3000 fb−1 and improve sensitivity to this rare process. This talk presents CMS searches for resonant and non-resonant di-Higgs production in the bbτ τ final state, which represents a good balance between high branching ratio and reduced background contamination. An optimized categorization has been developed for targeting boosted topologies, where the Higgs decay products become collimated, resulting in an improved separation of signal from background using new dedicated tagging algorithms. Higher luminosity will also bring harsher conditions, including increased radiation and pileup. To mitigate pileup, CMS upgrades include the addition of the MIP Timing Detector (MTD), which will enable 4D event reconstruction by associating precise time information of 30–60 ps to charged particles. This is expected to improve analysis sensitivity, especially those involving multi-object final states like di-Higgs searches, where the impact is equivalent to 2–3 additional years of data. This work focuses on the design optimization and performance validation of the Barrel Timing Layer (BTL), consisting of LYSO crystals coupled to Silicon Photomultipliers. These efforts were conducted via extensive test beam and laboratory measurement campaigns. Results confirm that the BTL meets its performance goal and its mass production is underway.