Several new physics models including versions of supersymmetry (SUSY) charac
terized by R-parity violation (RPV) or with additional hidden sectors predict the production
of events with top quarks, low missing transverse momentum, and many additional quarks
or gluons. The results of a search for top squarks decaying to two top quarks and six
additional light-flavor quarks or gluons are reported. The search employs a novel machine
learning method for background estimation from control samples in data using decorrelated
discriminators. The search is performed using events with 0, 1, or 2 electrons or muons
in conjunction with at least six jets. No requirement is placed on the magnitude of the
missing transverse momentum. The result is based on a sample of proton-proton collisions
at √s =13TeV corresponding to 138fb−1 of integrated luminosity collected with the CMS
detector at the LHC in 2016–2018. With no statistically significant excess of events observed
beyond the expected contributions from the standard model, the data are used to determine
upper limits on the top squark pair production cross section in the frameworks of RPV and
stealth SUSY. Models with top squark masses less than 700 (930)GeV are excluded at 95%
confidence level for RPV (stealth) SUSY scenarios.
