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Precision searches for new physics with boosted bosons combined

Subject Area Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 312958277
 
Final Report Year 2024

Final Report Abstract

The Run2 of the Large Hadron Collider (LHC) at a proton-proton center-of-mass energy of 13 TeV enabled probing electroweak boson pair production at invariant masses of multiple TeVs for the first time. Enhancements in boson pair production cross section are typical signatures of theories of beyond the standard model (BSM) physics like extra spatial dimensions or composite Higgs boson models that can provide a solution to the hierarchy problem. The experimental signature of high mass boson pair production is particularly challenging as W, Z and Higgs bosons primarily decay to a pair of quarks, forming at high momentum (Lorentz-boost) a single particle jet whose substructure must be resolved to identify its origin. The experimental techniques for the identification of boosted bosons with the CMS experiment have been significantly advanced in this project, including a new technique to mitigate additional collisions happening in the same bunch crossing (pileup) and improved identification algorithms making use of machine learning. In addition, new measurements of jet substructure have been carried out to reduce the dominant uncertainty in boosted boson identification and improve simulation models. Hints of a diboson resonance at masses of around 2 TeV from ATLAS and CMS seen in LHC Run1 have not been confirmed, excluding heavy-vector triplet resonances with masses below 2.4 TeV at 95% confidence level. With increased datasets corresponding to 36/fb, 78/fb and 138/fb, and advances in the analysis techniques, this mass limit has progressively been increased up to 4.8 TeV. At the same time, the mass spectrum of WW and WZ boson pair production has been studied for the first time up to 4 TeV to look for non-resonant enhancements. This analysis yielded the most stringent limits on anomalous WWγ and WWZ couplings, indicators of BSM physics at high energies, e.g. modifications of the Higgs sector. Diboson pair production remains a signature with discovery potential also in Run3 of LHC and at its successor HL-LHC with 2 times and 20 times, respectively, more collision data expected. The planned upgrades of CMS for the HL-LHC, have been shown to maintain jet substructure performance under the expected conditions with up to 200 pileup interactions and even improved. The importance of new detector concepts for jet substructure performance has been studied for future colliders beyond HL-LHC, motivating the development of highly granular calorimeters.

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