A search for ZZ and ZH production in the bbb¯ b¯
final state is presented, where H is the standard model (SM)
Higgs boson. The search uses an event sample of proton-proton collisions corresponding to an integrated luminosity
of 133 fb−1 collected at a center-of-mass energy of 13 TeV
with the CMS detector at the CERN LHC. The analysis introduces several novel techniques for deriving and validating a
multi-dimensional background model based on control samples in data. A multiclass multivariate classifier customized
for the bbb¯ b final state is developed to derive the background ¯
model and extract the signal. The data are found to be consistent, within uncertainties, with the SM predictions. The
observed (expected) upper limits at 95% confidence level are
found to be 3.8 (3.8) and 5.0 (2.9) times the SM prediction
for the ZZ and ZH production cross sections, respectively.