Probing New Physics: Search for supersymmetry with Higgs particles and high-precision luminosity determination at the CMS experiment

A search for supersymmetry (SUSY) is presented using high-energy proton–proton collision data from Run 2. The analysis tests the validity of the Standard Model (SM) by probing the direct production of SUSY partner particles, targeting events with a Higgs boson decaying to b quarks, an energetic photon, and large missing transverse momentum. Such signatures are indicative of undetected gravitinos as dark matter candidates in models with gauge-mediated SUSY breaking. Backgrounds are estimated using data-driven, semi-data-driven, and simulation-based techniques, with the dominant contributions incorporated into a statistical model for hypothesis testing. The sensitivity of the analysis is evaluated in terms of upper limits on the production cross sections and masses of the considered models. 

An alternative approach to testing the SM is provided by precision cross-section measurements, which require an accurate determination of the integrated luminosity. This work describes key contributions to the CMS Run 2 luminosity measurement, which achieved the lowest uncertainty reported for bunched hadron colliders, at 0.73%. A previously dominant systematic uncertainty, the factorization bias, is addressed in detail using two-dimensional van der Meer scans to extract the luminous surface, as well as an independent method based on luminous region information to reconstruct the bunch proton densities. A detailed study of the systematic uncertainties associated with the methods is performed. The two approaches are found to be consistent, reducing the associated uncertainty from up to 2% to below 0.4%.